Ashly DPX-100 User Manual

DPX-100

Graphic Equalizer

Compressor/Limiter

Operating Manual

Model DPX- 100
Graphic Equal izer
Compre ssor/Lim iter

10K

6.3K16K4K2.5K1.8K1K63040025018 0100634025

Gain

+6

+15

Range

+4

+10
+5
0

-5

-10

-15

±6dB

+2

±15dB

0

HPF EQ

-3

-9

-

dB

∞

20Hz

OutInOut

Sig Clip

0

-3

-6

-10

dB

Gain

Gain Reduction (dB) Input/Output Level (dB)

2Th. 4 6 8 10 12 14 16 18 20 -15-18 -12 -9 -6 -3 0 +3 +6 +9 +20

-3
0

-6

+3

+3

-10

+6

3

+6

-20

+10

+10

+20

2.5

+22-40

+15-15

dB

Thre shold Rati o Attac k Rele ase Output Level I n

5710

2

3

.5

2

1.5

20

1

30

.5

∞

.2 20

mS

1

5

.2

10

2

15

.1

3

Sec

-3

-6

-10

-20

∞

-

Clip

0

+3

+6

+10

+15

+20

dB

Output

Input

Power

ASHLY AUDIO INC.

847 Holt Road Webster, NY 14580-9103 Phone: [phone]

Toll-Free: [phone] Fax: [phone] Internet: www.ashly.com

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

Table Of Contents

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 UNPACKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 AC POWER REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4 MECHANICAL INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5 EQ CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.1 EQ Boost/Cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

5.2 Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.3 Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.4 HPF (Hi-Pass Filter) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.5 EQ In/Out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.6 Signal Present and Clip LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

6 COMPRESSOR/LIMITER CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

6.1 Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

6.2 Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

6.3 Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

6.4 Attack Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

6.5 Release Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

6.6 Output Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

6.7 In/Out Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

6.8 Threshold/Gain Reduction Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

6.9 Input/Output Meter Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

7 CONNECTIONS AND CABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

7.1 Balanced vs Unbalanced Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

7.2 Inputs and Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

7.3 Chain Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

7.4 Compressor/Limiter Detector Loop/Ducking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

8 TYPICAL APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

8.1 Graphic Equalizer Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

8.2 Compressor/Limiter Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

8.3 Special Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

9 DESIGN THEORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

10 BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

11 TROUBLESHOOTING TIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

12 WARRANTY INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

13 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

14 DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

15 SCHEMATICS

2

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

The lightning flash with arrowhead
symbol, within an equilateral triangle, is
intended to alert the user to the presence
of uninsulated "dangerous voltage"
within the product's enclosure that may be
of sufficient magnitude to constitute a risk
of electric shock to persons.

TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT R E­MOVE COVER. NO USER SERVICEABLE PARTS INSIDE.
REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.

TO REDUCE THE RISK OF FIRE OR ELECTRICAL SHOCK,
DO NOT EXPOSE THIS APPlIANCE TO RAIN OR MOISTURE.

TO REDUCE THE RISK OF FIRE, REPLACE ONLY WITH
SAME TYPE FUSE. REFER REPLACEMENT TO QUALIFIED
SERVICE PERSONNEL.

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

WARNING:

THIS APPARATUS MUST BE EARTHED

1. INTRODUCTION

The Ashly DPX-100 combines a 15 band graphic
equalizer and full function peak compressor/limiter in a
single rack space product. Both equalizer and compres­sor/limiter can be used as stand-alone processors, or can
be automatically chained together with a back panel
switch.

The graphic equalizer section uses professional
quality 25mm faders for maximum resolution and long
life. Ashly graphic equalizers use "Q" enhanced Wein
bridge filters with interleaved summing for constant "Q",
low ripple, and minimum filter interaction.

The Ashly compressor limiter circuit was de­signed in response to the need for unive rsal peak-sensi­tive automatic gain control (AGC) devices with
exceptional audio performance and rugged durability.
The result is a wide-bandwidth, ultra-low-distortion, low
noise VCA (voltage controlled amplifier) which is versa­tile and highly listenable.

Premium components are used throughout the
DPX-100, and computerized automatic assembly equip­ment verifies that each component's electrical specifica­tions are within tight tolerances before becoming part of
the circuit assembly. Each finished unit is then tested
twice before leaving the factory, guaranteeing you a
worry-free, professional product for many years.

Please read this instruction manual thoroughly
before operation so that you may realize all the features
and benefits the Ashly DPX-100 has to offer.

The exclamation point within an eqilateral
triangle is intended to alert the user to the
presence of important operating and
maintenance instructions in the literature
accompanying the device.

2. UNPACKING

As a part of our system of quality control, every
Ashly product is carefully inspected before leaving the
factory to ensure flawless appearance. After unpacking,
please inspect for any physical damage. Save the ship­ping carton and all packing materials , as they were care­fully designed to reduce to minimum the possibility of
transportation damage should the unit again require pack­ing and shipping. In the event that damage has occurred,
immediately notify your dealer so that a written claim to
cover the damages can be initiated.

The right to any claim against a public carrier
can be forfeited if the carrier is not notified promptly and
if the shipping carton and packing materials are not avail­able for inspection by the carrier. Save all pac king mate­rials until the claim has been settled.

3. AC POWER REQUIREMENTS

A standard IEC-320 AC inlet is provided on the
rear panel to accept the detachable power cord shipped
with the unit. Units distributed within the United States
are preselected for 120VAC, 60Hz and should be plugged
into a standard NEMA 5-15 3-wire grounded AC recep­tacle. Most units distributed outside the US are
preselected and labeled for 240VAC, 50-60Hz and are
shipped with the appropriate power cord.

The DPX-100 will perform normally from 95 to
125 volts AC. An internal line fuse is used. In the event
of fuse failure, refer to a qualified service technician for
servicing. Power consumption is less than 20 watts.

3

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

6.3K16K4K2.5K1.8K1K630400250180100634025

Model DPX-100
Gra phic Equ alizer
Compressor/Limiter

10K

+15

+10

+5

0

-5

-10

-15

Gain

dB

+6
+4
+2

0

-3

-9

-

∞

Range

HPF

20Hz

OutInOut

±6dB
±15dB

EQ

Sig Clip

4. MECHANICAL INSTALLATION

The DPX-100 mounts in a standard 19 inch
equipment rack. The mounting screw threads vary with
different rack manufactures and you should refer to your
rack instructions for proper hardware. An oval head or
flat head screw with a plastic countersink washer is pre­ferred to protect the finish of the DPX-100 under the screw.

This unit is housed in a rugged steel case and
will tolerate moderate abuse. However, for road systems
which may be dropped or otherwise subjected to extreme
forces, we recommend some rear support for the chassis
to prevent bending the front panel the front panel when
these forces occur.

For installations where it is desirable to protect
the front panel controls from tampering or accidental
misadjustment, use the Ashly security cove r. Installation
is simple and does not require removal of the equipment
from your rack. See your Ashly dealer for details.

5. EQ CONTROLS

5.1 EQ Boost/Cut

The individual equalization faders adjust the
boost or cut at each filter frequency. By adjusting a com­bination of faders, an overall frequency response can be
developed and the physical position of the f aders will gi v e
an approximate visual indication of this response.

5.2 Gain

The gain control adjusts the overall gain of the
equalizer when the EQ switch is “in”. It is generally used
to compensate for level changes due to the equalization
process, but can also allow the equalizer to adjust overall
system level and gain structure. Overall gain with this
control is from +6dB to -∞.

5.3 Range

This switch selects the operating range of the
individual equalization faders to either ±15dB or ±6dB.
The ±15dB settings should be used when much equaliza­tion is needed. The ±6dB setting allows finer resolution
on the fader settings.

5.4 HPF (Hi-Pass Filter)

The high-pass filter can be used to supplement
the frequency response achieved by the bandpass filters.
It’s function is to “roll off” low end response to eliminate

Ashly Securi ty Cover Installation

subsonic interference like wind noise, floor rumble, and
boomy microphone pops. The high-pass frequency is fixed
at 20Hz with an 18dB/octave slope.

5.5 EQ In/Out

This switches out the boost/cut controls and EQ
gain adjustments. This way, the effect of any equaliza­tion can be compared to a “flat” response. This switch
does not defeat the high-pass filter.

5.6 Sig and Clip LEDs

The signal present LED comes on when a signal
greater than -20dBu arrives at the EQ input. The clip
LED indicates any EQ signal level exceeding +19dBu.

4

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

-6

-10

Gain Reduction (dB) Input/Output Level (dB)

2Th. 4 6 8 10 12 14 16 18 20 -15-18 -12 -9 -6 -3 0 +3 +6 +9 +20

0

-3

+3

+6

+10

+15-15

dB

Gain

-10

-20

-3
0

-6
+3

+6

+10

+20

+22-40

dB

3

2.5

7

5

2

10

30

∞

20

1.5

1

.5

3

2

.2 20

mS

Threshold Ratio Attack Release Output Level In

6. COMPRESSOR/LIMITER CONTROLS

6.1 GAIN

The Gain control is used to adjust incoming sig-

nal level to the VCA circuit. It is always active, so

switching out the limiter function has no effect on this
control. Used in conjunction with the input/output level

meter display, this control is useful for setting up optimal
system levels. This control should normally be left at
"0" to achieve accurate threshold calibration.

6.2 THRESHOLD

The threshold control has a range of -40dB to

+22 dB, allowing applications from low level compres­sion to high level limiting. The threshold control de-

termines the audio level above which gain reduction
occurs. When the threshold LED comes on, that means

that gain reduction is beginning to occur, due to input
signal peaks exceeding the selected threshold in dB.

6.3 RATIO

This control determines the resultant change in

output level to changes in input level for all signals above
threshold. The numbers printed around the ratio con-

trol are calibrated in db and indicate the increase in
input (above threshold) required to produce a 1db in­crease in output. This can be expressed conveniently as

a ratio. If the output remains constant no matter how high
the input level, we have an infinite (∞) input/output ra­tio. It should be remembered that the ratio control has no
effect on signals which are below threshold.

There is a common but incorrect notion that lim­iting always implies the use of an infinite ratio. Although
there are times when an infinite ratio is desirable, there
will be situations where infinite, or “hard”, limiting ac­tion is neither appropriate nor necessary. In fact, it should
be noted that an infinite ratio setting is likely to cause
noticeable side effects in the sound, and may not be us­able on programs where subtle control is desired.

Clip

-6

-10

-20

0

-3

-

+3

+6

+10

+15

+20

∞

dB

Output

Inpu t

.5

Sec

1

2

3

5

.2

10

15

.1

Power

6.4 ATTACK TIME

The response of the compressor/limiter to signal

levels abov e threshold is further defined by the attack time
control. Attack time is the amount of time it takes to

attenuate the output level after threshold has been
reached. For v ery fast transients, such as hand claps, snare

drums, or other percussive sounds, a fast attack time is
usually desirable so that the limiter can respond in time
to control the peak level. On other types of program ma­terial, a slower attack time may be preferred. An abrupt
attack may, on some material, “square off” the top of a
waveform, producing a distorted sound . The DPX-100 pro­vides continuously variable attack times from 200 micro­seconds to 20 milliseconds.

6.5 RELEASE TIME

Another parameter which affects compressor/lim-

iter performance is release time, or the time required to

restore system gain to normal after the input signal
has fallen below threshold level. Again, proper release

time will depend on the type of program material being
processed and the way in which the limiter is being used.

When subtle limiting is desired, slow release
times are often chosen to avoid condition referred to as
“pumping” or “breathing”. This occurs when overall gain
is modulated up and down by repeated peaks which are
followed by quieter intervals. If the release time is set
too fast, then the overall level will jump up and down,
producing an objectionable and unsettling effect. Note
that, in some cases, an individual track or channel which
seems to be pumping may sound acceptable when heard
in context of a complete mix.

A unique feature of Ashly Compressor/Limiters
is the incorporation of a double release-time constant.

When a conventional compressor/limiter is adjusted for
slow release times, transients such as mic “pops” may
cause a severe reduction in gain followed by a slow fade­up, making the action of the limiter very obvious. With

5

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

M

G

p

AC

Model DPX-100

Made In USA

CAUTION

100-120VAC

50-60Hz 12W

Risk o f Electric

Shock. Do

Not Op en

the double time constant, release from gain reduction af­ter a brief transient is always fast, with a slower release
after a sustained overdrive.

6.6 OUTPUT LEVEL

Output level control is provided to fully cut or
restore up to 18 dB of system gain. For unity gain, set
the control to 0. NOTE: When the compressor/limiter is
switched out, the output control still functions.

6.7 IN/OUT SWITCH

This switch enables you to quickly hear the com­pressor/limiter in or out of the audio chain. When the
switch is in the out position, all limiting and compres­sion controls and functions are bypassed, with the excep­tion of the gain and output controls, which continue to
function as straightforward level controls.

INPUTS are Active B alanced.
OUTPUTS May Be Wired
B a la n c e d O r Un ba la n c e d .

3

2

XLR

1

Fem ale

Shown

(-)(+)

Output

6.9 INPUT/OUTPUT METER SELECT

While the Gain Reduction display accurately rep­resents the action of the limiter, comparing input to out­put levels in real time is somewha t more intuitive, and is
made simple using the input/output meter select switch.
The input meter takes its signal just after the gain con­trol, and will indicate input signal level regardless of out­put levels or limiter settings. The output meter display
takes its signal from the actual output of the unit, so ev­ery control that affects the output will also have an effect
on output meters. Used in conjunction with the gain re­duction meters, input/output meters prove to be an ex­tremely useful diagnostic tool when working with system
dynamics and level control.

7. CONNECTIONS AND CABLES

Com

TIP = Detec

(Use

RIN

6.8 THRESHOLD/GAIN REDUCTION DISPLAY

As soon as the threshold level is reached, the yel­low LED illuminates. Depending on how far the input
level rises above threshold, successive red LED’s will il­luminate, indicating gain reduction. Gain reduction can

best be described as the difference between input level
and the resulting change to output level. For signals

below threshold, there will of course be no gain reduc­tion, that is, a 10dB increase in input will yield a 10dB
increase in output. For signals above threshold however,
output level will increase only to the extent that the ratio
control allows. With a high ratio, say 20 or so, it will take
20dB of increased input level to increase output level by
1dB. With a gentler ratio of 3:1, input signals above
threshold will be “gain-reduced” at the output by 1/3. In
other words, with threshold set at 0dB, a signal peak at
+12 dBV that is 3:1 compressed (ratio at 3) will produce
only +4 dB (12÷3) at the output, and 8 dB of gain reduc­tion has occurred (12 dBV input minus 4 dBV output=8
dB reduction.)

7.1 Balanced vs. Unbalanced Audio Connections

Balanced signal connections are preferred in pro
audio applications because of their improved immunity
to induced hum and noise. A properly shielded and wired
balanced input stage on any audio product will reject most
unwanted noise (RFI, EMI) picked up by the cable, as
well as minimize ground loop problems. Therefore it is
always advantageous to use balanced connections when
running signal more than ten or fifteen feet, although par­ticularly noisy environments may require that ev en short
patch cables be balanced.

Unbalanced connections are used mostly for short
distance, high level signals (0dBu nominal). Most exter­nal EMI noise pick-up will be masked under the noise
floor of the signal, assuming there is little or no gain fol­lowing the unbalanced signal. If a gain stage does follow
a signal, or if externally sourced noise persists, use bal­anced connectors.

6

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

pressor/Limiter Graphic Equalizer

ector Retu rn/ Ducking Input

Mono Plug For Ducking)

ING = Detector Send

PUSH

Chain

In

Detector

Input

7.2 Inputs and Outputs

The DPX-100 uses two different audio connec­tor types. 1/4" TRS (tip-ring-sleeve) phone jacks, and
three pin XLR connectors will allow interfacing to most
professional audio products. Ashly TRS balanced con­nections use the tip as (+) and the ring as (-) signal, with
sleeve used for ground. Ashly XLR connectors use pin 2

Out

Output

7.3 Chain

The chain button on the back panel allows the
output of the equalizer to be fed directly to the input of
the compressor/limiter, with no external cable required.
When the chain switch is in, the input connectors to the
compressor/limiter are removed from the circuit, while
the graphic equalizer outputs remain functional.

(+) and pin 3 (-) with pin 1 ground. Inputs are 20KΩ
active balanced using precision 1% metal film resistors ,

7.4 Detector Loop - Ducking

outputs are 200Ω "pseudo-balanced", which means they
have balanced impedance with a single-ended signal
source, and can be wired balanced or unbalanced. When
possible, we recommend balanced connections between
all components in your system.

sert DETECTOR PATCH point which can be used as a
"ducking" input, or in conjunction with an equalizer to
produce frequency-sensitive limiting. Various uses of the

The DPX-100 compressor/limiter has a TRS In-

detector patch are discussed under TYPICAL APPLICA-

If inputs are used unbalanced, the signal should

TIONS.

be on the (+) connection and the (-) connection must be
tied to ground, or signal loss will result. While a mono

phone plug used as an unbalanced connection will auto­matically ground the (-) ring of the jack, XLR's will not

8. TYPICAL APPLICATIONS

automatically do this, so attention must be given to proper
wiring.

By itself, the 15 band graphic EQ is useful for
general tone control, feedback control, and room reso-

Tip (+)

Ring (-)

Sleeve (Gnd)

Stereo Phone Plug
used for balanced

nance correction. The compressor/limiter provides many
solutions where dynamic signal level processing is re­quired. The combination of graphic EQ and compressor/
limiter allows for additional applications, such as a full
range speaker processor, 70 volt distributed system pro ­cessor, mixing console channel insert, and frequency sen­sitive limiting, to name a few. In most cases, the DPX-100

Tip (+)

Sleeve (Gnd)

Mono Phone Plug
used for unbalanced

should be the last device before the power amp or cross­over, or right before a recording device or transmitter.

8.1 GRAPHIC EQUALIZER APPLICATIONS

PUSH

Input

XLR pins are
numbered
on the
connector
insert.

2 = (+)
3 = (-)
1 = (gnd)

Audio C onnector Types

XLR Male

XLR Female

General Tone Control

The graphic equalizer is a very useful device for
general tone shaping because it is intuitive and easy to
adjust. The visual reference provided by the slider posi­tion gives an approximate idea of the frequency response
generated, with the lower frequencies on the left and
higher frequencies on the right. To use the power of an

7

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

equalizer effectively, you need to translate your idea of
the tone you want to produce into a range of numerical
frequencies. This is simple after a little practise. Here are
a few references which are useful for starting points:

- Very low bass (the “wind” in a kick drum,
almost felt as much as heard -40Hz-80Hz.

- The low register of a male voice - 200Hz

- The low register of a female voice - 350Hz

- Lower midrange (“warmth” frequencies) ­400Hz-1KHz

- Upper midrange (“harshness”, snare drum
“bite”, “hot” sound) -2.5KHz-4KHz.

- Sibilance (“sss” sounds, cymbal “sizzle”) ­8KHz-15KHz.

Try using these starting points as a guide when
you want more or less of these types of sounds. Adjust
by ear from there. It is always a good idea to remember
that a little equalization usually works out much better
than a lot, and that there are many audio problems which
can not be solved with equalization alone.

Feedback Control

A graphic equalizer can be used to provide some
control over moderate feedback problems, but does not
have enough flexibility or resolution to handle sev ere situ­ations. You will achieve the best results when you can
eliminate one or two feedback points by setting one or
two sliders for no more than a 6dB cut. Often you can
find a feedback point by boosting sliders in succession to
determine which frequency ranges contain the feedback
modes, and then cutting those ranges. Be very careful in
this process to avoid explosi ve feedback and possible sys­tem and hearing damage! If you find feedback points
with many equalizer bands, remember that cutting every
band may not help (all you will do is reduce system gain).
The combination of a graphic equalizer for tone control
and a parametric equalizer (such as the Ashly PQX-571
or PQX-572) for feedback control is highly recommended.

Console Channel Equalization

Many mixing consoles provide only simple equal­ization for individual channels. If your console has chan­nel inserts, you can patch your graphic equalizer into a
channel that’s being used for something important and
use it to tailor the sound of this channel exactly the way
you want.

Large Room Equalization

Large rooms tend to suffer from multiple reflec­tions with long time delays, long reverberation times, and
“ring-modes”, all of which lead to reduced intelligibility
and a generally “muddy” sound. As sound travels long
distances through the air, high frequencies are attenuated
more than low frequencies. In general, large rooms ben­efit from some low frequency roll-off, high frequency
boost, and attenuation of ring mode frequencies. As in
the case of feedback control, a graphic equalizer can help
reduce an isolated ring-mode or two, but a tunable nar­row-band equalizer such as a parametric is more effec­tive here.

8.2 COMPRESSOR/LIMITER APPLICATIONS

As the functional name implies, a compressor/
limiter can be divided into two basic categories, limiting
and compressing. When used as a protective device to
prevent audio levels from overloading systems such as
tape recorders, power amplifiers, speakers, or transmit­ters, it is generally referred to as a limiter.

It may also be used to create special effects and
unusual sounds for recording and musical performance
by deliberately reducing the dynamic range of a signal,
creating a much louder or fuller sounding signal without
increasing the loudness peaks, in which case it is referred
to as a compressor.

The Limiter As A Protective Device

The DPX-100 compressor/limiter section pro­vides fast and accurate gain control for the prevention of
sound system overload due to unexpected transients.
Sound system distortion is usually the result of amplifi­ers running out of power, in which case nice round wave­forms turn into harsh sounding squared-off waveforms.
Looking at it from the perspective of the speaker dia­phragm, this means that, whereas in normal operation the
diaphragm is required to accelerate, slow down, smoothly
change direction, and accelerate again, distorted opera­tion requires an instant acceleration, instant stop, a change
of direction, and instant acceleration again.

Since speaker diaphragms are subject to the laws
of physics, they won’t take this kind of punishment for
long. The diaphragm may shatter, or its voice coil may
overheat. In addition to the damaged caused by sustained
overload, the speaker may also be damaged by occasional,
one-shot high level overload, for example, the sound of a
microphone falling face-first onto a hardw ood floor . Even

8

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

if this type of transient doesn’t destroy a speaker outright,
it may damage the speaker surround in such a way as to
cause mechanical abrasion and future failure.

Alternatives For Sound Installations

To install a compressor/limiter in a sound sys­tem using a passive crossover, insert it between your mix­ing console output and the power amplifier input. For
systems using electronic crossovers, there are two ways
to use a compressor/limiter. It may be inserted between
the mixer output and the crossover input, in which case it
will act on the entire audio frequency spectrum. Alter­nately, if the limiter is inserted between an output of the
electric crossover and the input of a power amp, it will
only affect a specific band of frequencies.

Recording

The Ashly limiter can be used to prevent tape
saturation in analog recording. Also, with modern trends
toward inexpensive digital recording, it remains neces­sary to protect against input overload. With digital re­cording, the information stored on tape, hard disk, optical
disk, etc., is either a 1 or 0, so actual signal level on the
tape is not the concern it is with analog recordings, in
fact it is not even a user controllable parameter. What is
of concern however, is the signal level applied to the A-D
(analog to digital) converters. If clipping occurs at the
converter input stage, the resulting distortion is most un­pleasant, and will be recorded digitally as if they were
part of the original audio signal, forever mixed with the
audio. To prevent converter distortion while preserving
the extended dynamic range of digital recording, look up
the max input level of your recorder/conve rter and set up
the limiter as follows:

1. Set Gain to 0.

2. Set Threshold to 2-3 dB below max conve rter

input.

3. Set Ratio to 10.

4. Set Attack to 2 mS.

5. Set Release to .2 Sec.

6. Set Output level to 0.

If you are exceeding threshold frequently, your
input signal is probably too high and should be turned
down. Of course, eve ry situation is different, so experi ­mentation before final recording is always a good idea,
but this is a good starting point.

To obtain a gentler limiting action a t the expense
of some dynamic range, decrease the threshold to -15 and
the ratio to 3-5. This is also a good starting point for
analog recording.

Broadcasting

Compression has long been used as a
tool to make an audio signal appear louder. A
good example is in broadcasting, where com-

peting stations with identical transmitters and power at­tempt to sound louder than each other. Since they are all
restricted with respect to maximum audio level (modula­tion), their best tactic is to squeeze the dynamic range of
their programs to just a few dB. The audio output level
of the station virtually never changes, and the listener
perceives this continuous high-lev el sound as being louder
than the same material in an uncompressed form. Although
both compressed and uncompressed programs reach the
same peak levels, the compressed signal stays near peak
level more of the time, and thus sounds louder. This tech­nique makes the broadcast more intelligible over ambi­ent noise, and increases the geographical area over which
the broadcast is audible to the listener. Additionally, this
compression technique is extremely useful for FM and
infrared transmission systems for the hearing impaired.

8.3 Special Effects

Compression For Feedback Contro l

A common ritual in sound system set-up is equal­izing the room to remove feedback. This is generally
accomplished by turning up system gain to purposely in­duce feedback, searching for the center frequency of the
feedback, and then equalizing at that frequency to remove
the feedback. Once this frequency has been cut, system
gain is again increased to induce another feedback point,
and the whole procedure is repeated until the engineer is
satisfied that the significant problem frequencies have
been corrected. The major problem with this approach is
that the feedback can easily get out control, and the engi­neer ends up dashing back and forth between the mixer
volume controls and the equalizer controls, while every­one in the room plugs their ears and prays it will end
soon. The Ashly DPX-100 can turn this procedure into a
fast, painless job, eliminating loud feedback levels and
the possibility of speaker or ear damage.

Procedure:

1. Set up the DPX-100 limiter controls

as follows:

a. Output level control to -20dB.
b. Input Gain control to 0dB.
c. Threshold control to -30dB.
d. Ratio control to infinity (∞)

9

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

e. Attack time to 5mS.
f. Release time to 1 Sec.
g. Limit switch IN

2. Using a 1/3 octave (31 band) or parametric
equalizer, set the EQ controls to a flat setting, and if the
equalizer has an overall volume control, boost it by 10 to
15 dB.

3. Open up several microphone input channels
to a normal operating level, with typical EQ settings, and
turn the console master fader up to a louder than normal
setting. At this point, the system should be well into feed­back, but the room volume will be constant due to the
action of the limiter. You can listen to the feedback at
any level you like by simply varying the limiter output
level control, although below a certain monitoring level,
the feedback will stop.

4. Try to determine the feedback frequency, and
then equalize it by adjusting the center frequency, band­width, and boost/cut controls of your parametric equal­izer. (Note: a graphic equalizer can also be used, although
with less accuracy.) After eliminating the problem fre­quency, try to further define it by sharpening up the band­width, reattacking the frequency control, and making the
cut shallower, if possible.

5. As soon as the first feedback frequency has
been removed, the compressor/limiter will automatically
bring up system gain until another feedback point is in­duced. Repeat the equalization procedure until it becomes
impossible to distinguish individual, predominant feed­back frequencies.

6. Write down EQ marks for safekeeping if nec­essary, and return all mixer, EQ master gain, and com­pressor/limiter gain controls to normal operational
settings.

Altering the Texture of Musical Instruments

It would be impossible to mention here all the
ways that compression is used to create new sounds with
familiar instruments. Some typical uses are:

1. Creating a “fatter” kick drum or snare sound.

2. “Thickening” acoustic guitars.

3. Adding punch and sustain to electric bass or

guitar.

In general, use a gentle compression ratio, say
4:1, with a 10 mS attack time, 0.1 Sec. release time, and
a low enough threshold to cause 6 to 10dB of Gain Re­duction. Try using this effect to help bring out a lead

vocal or instrumental solo in a cluttered mix. The com­pressor is also a great corrective tool when working with
singers whose own dynamic control is less than perfect.
A little compression helps to keep their quieter lines from
becoming buried in the mix. Experimentation is highly
recommended.

Voice-Over Compression (“Ducking”)

The compressor/limiter can be used to automati­cally reduce music to a background level when an an­nouncer is speaking. In this scheme, only the music signal
is actually gain-reduced by the limiter. However, the de­tector is connected to respond to an announcer’s voice
instead of the music’s peaks. Voice-Over compression
assumes you are already using some sort of mixer to com­bine the music and mic signals. Use the direct out (send)
of the mic channel to feed the detector input on the CLX
unit. Note: Be sure to use a mono plug for the CLX
detector input. Then use the Threshold and Ratio con­trols to determine when and by how much the announcer’s
voice affects the music level.

De-Essing

A special type of saturation problem often en­countered in recording is the sibilant (Ssss) sound of the
human voice. High frequency, sibilant sounds can reach
very high energy levels, so that a voice that is otherwise
undistorted breaks up on the esses, producing a raspy, un­desirable sound. With analog recording to magnetic tape,
high frequencies tend to saturate the tape sooner , and com­bined with the internal high frequency boost (record pre­emphasis) on standard tape decks, the need to control
sibilants becomes apparent.

The solution is frequency-dependent limiting,
which is easily accomplished with the DPX-100. By in­serting an equalizer into the Detector Patch point and
boosting the equalizer at high frequencies in the vicinity
of the sibilant, the limiter’ s detector circuit becomes mor e
sensitive to this particular range of frequencies, and so
will limit the bothersome sibilants more than other fre­quencies.

Realize that this technique is very different from
simple equalization. Equalizing a sibilant vocal by cut­ting high frequencies would result in a loss of important
high frequency information at all times, whereas de-essing
has no effect whatsoever on the signal except at the in­stant of the sibilant. At that moment, the Ashly limiter
will reduce overall gain. Frequency response is unaf­fected, and the sibilant is controlled.

10

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

9. DESIGN THEORY

Graphic Equalizers: The Basics

While most graphic equalizers look very much
the same, there are several important differences in the
circuitry used to implement various designs.

Perhaps the major differences are in the filters.
Some equalizers use a filter made of a capacitor, an in­ductor, and a resistor, or “RLC” filter. The advantage
here is simplicity, but the real disadvantage is the induc­tor itself. An inductor is a coil of wire with a core of
some sort. Inductors are susceptible to hum fields and
they are large and expensive.

Other equalizers use the same basic approach, but
replace the inductor with a “simulated inductor”, which
is actually a circuit comprised of an amplifier, a capaci­tor, and a couple of resistors. This adds parts but is less
expensive than a real inductor. The problem with this
approach is that simulation is less than ideal; it produces
an inductor with high resistive loss resulting in poor curve
shape when used in a filter.

The summing system in a graphic equalizer is
also important. Since there are a number of filters which
combine to produce the overall response, it is important
that the filters not interact (they WILL overlap, but the
response of one filter should not modify the response of
another). Ashly uses an “inter leaved” summing system
where every other filter uses the same summing amplifier
so that adjacent filters never share the same drive and
feedback signals. This allows the filters to maintain their
natural response.

Compressor/Limiters: The Need For Gain Control

The human ear excels in its ability to detect an
extremely wide range of loudness levels, from the quiet­est whisper to roar of a jumbo jet. When we attempt to
reproduce this dynamic range, by means of amplifiers,
tape recorders, CD players, or radio transmitters, we run
into one of the fundamental limitations of these electronic
media: limited dynamic range. Amplifier dynamic range
is quite good, and is adequate for most musical program
material. However, some types of audio equipment, such
as cassette tape recorders, have a very narrow useful dy­namic range.

Another problem with “RLC” designs is that large
capacitors must be used for the lower frequency filters,
limiting the choice to large, expensive non-polar types or
electrolytic capacitors with poor audio performance. Also,
when this filter type is combined with a potentiometer to
adjust the equalization, the resistance of this pot affects
the “Q” of the filter so that a little equalization produces
a much broader curve than a lot of equalization.

The other filter approach is a true bandpass fil­ter. This can be made with no inductors and more practi­cal sized capacitors; the “Q” is easily set and remains
constant, and the parts count is reasonable. there are sev­eral types of bandpass filters suitable for this job. Ashly
uses a “Q” enhanced Wein-bridge filter. Because it is a
symmetrical design using matched tuning components,
the “Q” is easily set and is very stable.

In designing a graphic equalizer, a selection of
filter sharpness must be made. More sharpness (higher
Q) produces less filter overlap and tighter control over an
individual band, but also causes ripple in the frequency
response when many filters are boost or cut together to
produce a flat response. We feel that the graphic
equalizer’s primary use is for “voicing” and tone control,
and have set our filter sharpness to produce a maximum
of 1dB ripple.

What is it that compromises the dynamic range
of this equipment? The useful operating region of a piece
of audio equipment is squeezed in between noise and dis­tortion. As program level decreases, it approaches what
is known as the “noise floor”, and if the volume of the
program material goes lower still, it is engulfed by the
noise. The noise floor, or minimum constant noise leve l,
will consist of hiss, hum, transistor noise, tape hiss, buzz
and whatever noises are inherent in the medium. When
the program level is considerably higher than the noise
floor, our hearing masks the noise, and it is not a prob­lem. However, when listening to very quiet sections of a
program for example, a pause between movements of a
string quartet the noise can become very bothersome.

At the other end of the loudness spectrum, the
limitation on dynamic range is usually distortion, either
in the form of amplifier overload, tape satu ration, or A to
D clipping. In most transistorized equipment, the transi­tion from clean, undistorted operation to severe distor­tion is very abrupt. Therefore, it is common practice to
operate a piece of equipment at a level that is somewhat
below the distortion point, leaving a margin of safety for
unexpected, transient volume peaks in the music. This
safety margin is known as headroom, and may range from
10 to 25 dB. Lowering our standard operating level to
leave ourselves some headroom helps prevent distortion,
but at the same time it moves our ave rage program level
closer to the noise floor, thereby compromising signal­to-noise performance. It becomes apparent that to get most

11

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

out of an audio system, you have to keep your standard
operating level as high as possible without risking distor­tion.

GAIN RIDING

One solution to the noise vs. distortion trade-off
is to keep your hand on the level control and manually
adjust gain to suit the program. Indeed, there are times
when this approach is entirely satisfactory. However, in
most types of music there are instantaneous, short dura­tion volume peaks, or transients, which would be difficult
to anticipate and impossible to respond to with manual
gain riding, you simply could not bring the level down
fast enough. In many situations, this can present real prob­lems. For example, in recording, an extra burst of enthu­siasm from a lead singer might overload the capabilities
of your recording tape, causing ragged distortion and ne­cessitating another take. In sound reinforcement, a sud­den burst of energy through the system can blow fuses or
even damage loudspeakers.

In addition to the problem of response time with
manual gain riding, it also requires your constant atten­tion, which takes you away from more important jobs. The
need for a fast-acting, reliable, automatic gain control is
answered by limiters and compressors.

WHAT COMPRESSORS AND LIMITERS DO

LIMITING

In any musical program are constant changes in
loudness. It is the job of a limiter to detect when the vol­ume has exceeded a predetermined maximum safe level,
and to then turn down the volume. When the incoming
signal returns to its original level, the limiter should re­spond by restoring the gain to normal. Thus, when the
level is within a specified “safe” range, the limiter has no
effect. When an occasional peak occurs, the limiter re­sponds. This situation is completely analogous to manual
gain riding, except that it occurs faster and more consis­tently.

COMPRESSION

A very significant difference in dynamic range is
achieved simply by changing the relationship between nomi­nal signal level and threshold, as a result of either increas­ing the GAIN and/or decreasing the THRESHOLD control.
The most interesting effect to be noted, how ever, is seen by
comparing the original input signal with the output signal.
The quietest portions of the original signal will be effec­tively increased in volume while the loudest portions of the
original signal will be decreased. In effect, both ends of the

dynamic spectrum will be pushed toward the “middle”.
This is quite different from simple limiting, where only
loud peaks are subjected to gain reduction. More than
anything else, it is this double-ended effect which dis­tinguishes compression from limiting. Compression is
further differentiated from limiting by careful selection
of attack and release times. When limiting is employed
to protect an audio system against transient volume peaks
and possible overload, attack time is usually set as fast
as possible, consistent with distortion-free performance.
Release time would also be relatively short, so that the
output signal would be restored to normal as quickly as
possible after the transient.

Compression is frequently used to keep over­all signal level within a specific dynamic range, and
for this application, slower attack and release times
are usually chosen. This approach is analogous to our
manual gain riding example, where our operator is fad­ing the music up and down to keep it fairly constant,
but is doing it slowly enough so that the listener is un­aware that the gain is being altered.

Voltage Controlled Amplifiers

Early VCA’s wer e based on vacuum tubes with
a “remote cutoff” characteristic. The tube would sim­ply change its gain in response to a changing bias volt­age. Tubes developed for this purpose did an excellent
job, in fact they could exceed the noise and distortion
performance of today’s best solid state VCA’s. Unfor­tunately, they also had some serious disadvantages pe­culiar to tubes - change of gain and matching as aging
took place, heat, microphonics, high cost, and the need
for both high-voltage and filament power supplies.

Over the years the need for good, low-cost,
solid state VCA brought about many innovative ap­proaches. A good example is the electro-optical at­tenuator where a photocell is used as one leg of a
potentiometer. Since the photocell behaves as a true
resistor, distortion and noise are very low. Unfortu­nately, the response time of photocells is slow and un­predictable so their use in a fast peak-limiter is really
not feasible. Also, the matching between units is very
poor so that stereo tracking is not possible without te­dious hand-matching of photocells.

Another approach uses a field-effect transis­tor (FET) as a variable resistor. Here, at least, the re­sponse time is fast (in the nanosecond range), but
matching between units is still poor, requiring hand
matching for stereo. An additional problem is that a
FET will only act as a pure resistor with very small
signals applied so it is necessary to attenuate an input

12

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

signal before the gain control FET and then amplify it
again. Of course this results in less than ideal noise per­formance and imposes a frustrating trade-off: less noise
= more distortion.

A number of VCA’ s based on the exponential volt­age-current characteristic of a bipolar junction transistor
have been used. One of the most common is called a
“transconductance amplifier”. Using the inherent match­ing obtained by integrated circuit technology, these de­vices have very predictable control characteristics.
Tracking within 1dB over a 40dB range is common. Not
only do the control characteristics match well from unit
to unit, but they can easily be made exponential (loga­rithmic) so that even increments of control voltage pro­duce even increments of gain change in decibels. The
response time is also very fast.

The problem with simple transconductance am­plifiers is that, like FET VCA’s, they can handle only very
small signals so the noise performance is poor. A num­ber of linearizing circuits have been devised to minimize
this problem, but even the best transconductance amplifi­ers have an equivalent input noise of about -80dBv, which
compares poorly to straight linear amplifiers.

The best analog compromise to date is the “class
AB current ratio multiplier.” Early implementation of
this circuit used two matched pairs of transistors, one pair
of NPN’s and one pair of PNP’s. The problem here is
that excellent matched integrated NPN pairs were avail­able, but integrated PNP’s were not. The PNP’s had to be
hand-tested and matched. Careful trimming was neces­sary for low distortion and even minor temperature
changes made re-trimming necessary because of differ­ing characteristics between the two types.

The Ashly VCA

The Ashly VCA is an inte grated current ratio mul­tiplier circuit. It has low noise (-90dBv), low distortion
(.05%), excellent response time and tracking and does
not suffer from thermal drift. The noise and distortion
are at state-of-the-art levels and the circuit is consistent
in mass production with minimal trimming and no hand­selection of transistors.

Detectors

It would seem that, of the two components in a
compressor/limiter, the VCA is the more critical since the
audio passes through it and the detector only provides it
with a control voltage. Experience showed us that both are
crucial to the overall sound and that, if anything, the
detector’s perf ormance is the harder to judge by conven-

tional measuring techniques. While the VCA is doing its
job if it has low noise and distortion, the detector must con­stantly adjust the gain of the audio path in a manner which
keeps the level under control while sounding acceptable to
the listener. This constantl y changing gain is a dynamic
action, while conventional audio measurements like noise
and distortion checks are Static (at a constant level). We
became painfully aware of this problem with some of our
earlier limiter prototypes which measured fine and sounded
terrible. This led us to use a purely subjective approach in
the design of the detector - we did a lot of listening to de­termine what sounded good and what didn’t.

Two important features emerged from this re-

search:

1. We designed the detector to let the attack and
release times speed up as more and more limiting occurs.
The compression ratio also increases. This lets us main­tain peaks fairly close to a constant ceiling level, but al­lows the illusion of increasing loudness as input level
increases, thereby preventing complete loss of dynamics
when limiting.

2. We incorporate a double release time constant.
When release time was set slow with a single time con­stant, transients such as mic “pops” caused a quick re­duction in gain and a slow fade-up, making the action of
the limiter very obvious. With the double time constant,
release from gain reduction after a brief transient is al­ways fast, with a slower release after a sustained over­drive.

When choosing a compressor/limiter, you can see
that it is very important to listen to it in your particular
application and see that it sounds the way you want. There
are lots of these devices with seemingly excellent specs
which sound very different with real program material
applied to them.

Peak Or RMS

There are several ways of looking at a signal to
determine its level. A peak detector looks at the maxi­mum voltage a signal reaches regardless of it’s waveform,
while an RMS (root mean square) detector looks at the
energy in a signal regardless of the short term voltage
levels. This makes a peak detector the correct choice for
preventing clipping, overmodulation, or tape saturation,
while an RMS detector can be used to restrict material to
a given loudness. When an RMS limiter is used to pre ­vent clipping, the result is unpredictable. For instance, a
flute and a snare drum which are limited to the same RMS
level might have peak levels as much as 30dB apart! Use
peak limiters to prevent clipping.

13

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

10. BLOCK DIAGRAM

2

3

1

2

3

1

EQ

INPUT

-

-

+

+

LIMITER

INPUT

-

-

+

+

GAIN REDUCTION DISPLAY

RATIO

ATTACK

RELEASE

HPF

CHAIN

GAIN

GAIN

INPUT/OUTPUT METERS

DETECTOR

CIRCUIT

11. Equalizer Troubleshooting Tips

No Audio Output

Check AC power - is the pilot light on?
Check in/out connections - are they reversed?
Are you sure you have an input signal?

6dB/15dB

15 BAND EQ

EQ In/OutHPF In/Out

VCA

CHANNEL
IN/OUT

TH

THRESHOLD

OUTPUT

LEVEL

Distorted Sound

This will only be caused by too much
signal which will show on the Clip LED. If the
LED is not flashing, there is an overload some-

SIG

where else in the signal path. Adjust the rela­tive gain of each component in your chain to

CLIP

2

3

1

keep everything at a comfortable level.

Excessive Hum or Noise

Hum will usually be caused by a ground
loop between components. Try using the sug-

EQ OUTPUT

gested balanced input and output hook-ups if the
other pieces of equipment used in conjunction
with your equalizer have balanced inputs and
outputs.

CLIP

Noise (excessive hiss) can be caused by
insufficient dri ve signal. Make sure you are send-

2

3

1

ing a nominal 0 dBu line level signal to the
equalizer. Most noise problems occur because
gain is applied to audio signals too late in the
chain. For best performance, apply gain to in-

LIMITER
LIMITER

dividual source signals as early as possible, like
at the mixer input preamp section. As gain in­creases, it also boosts the noise content of that

DETECTOR

INSERT

signal. An y cumulative noise b uilt up in a mixe d
signal will only be increased by using an equal­izer as a gain device, so make eve ry attempt to
operate the equalizer with as little gain as pos­sible.

Note: Unshielded cables, improperly wired con­nectors, and cables with broken strands of wire are very
common problems. Use quality cables with quality, cor­rectly wired connectors.

11.1 Compressor/Limiter Troubleshooting Tips

EQ Controls Do Nothing

Is the master EQ switch in?

The lowest and highest frequency sliders may be
beyond the range of the program material or speakers and
may produce little or no audible effect.

Peak Light Flashes or Stays On All the Time

If the peak light flashes, the signal level to the
equalizer is too high. Turn down the gain. If it is on all
the time, disconnect the input and output cables. If it is
still on, the unit must be returned for service.

14

No Output

Check A C power . Is the po wer switch on? Check
input and output connections - are they reversed? Are
you sure you have an input signal?

Controls Have No Effect

Is the limiter in/out switch in? Perhaps the ratio
control is set too low to produce an audible effect or the
input lev el is belo w threshold. Is the threshold LED light­ing up? If not, lower the threshold setting or increase the
gain. Do not expect to hear any effect when the input
level is below threshold, since the unit is simply a linear
amplifier at those levels.

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

When Using Heavy Compression, Background Noise
Is Noticeable During Quiet Sections Of The Program

As defined in the section on compression, quiet
program material is effectively made louder while loud
peaks are made quieter. When the program source is thus
raised in volume, its noise floor is also raised in volume
by a proportionate amount. This is not a defect in the
compressor/limiter, but an unavoidable side effect of the
gain altering process. If the noise becomes a problem,
the solutions are to either decrease noise at the program
source, or use less compression.

Excessive Hum Or Noise

Hum is often caused by a “ground loop” between
components. Try using the suggested balanced input and
output hookups if the other pieces of equipment used in
conjunction with the DPX-100 have balanced inputs and
outputs. Noise can also be caused by insufficient drive
levels. Make sure you are sending a nominal 0 dBV line
level signal to the unit.

12. WARRANTY INFORMATION

Thank you for your expression of confidence in
Ashly products. The unit you have just purchased is pro­tected by a five-year warranty. To establish the warranty,
be sure to fill out and mail the warranty card attached to
your product. Fill out the information below for your
records.

Model Number ______________________________

Max Level . . . . . . . . . . . . . . . . +23dBu

Output Connectors . . . . . . . . . 1/4" Phone Jack, XLR

Frequency Response . . . . . . . . ±.25dB 20Hz-20kHz

THD (20Hz-20KHz) . . . . . . . . <.01%@+20dBu

IM Distortion (SMPTE) . . . . . <.01%@+20dBu

Output Noise (20Hz-20KHz) . <-100dBu

Gain Control . . . . . . . . . . . . . . −∞ to +6dB

(EQ in, all faders flat,
20Hz-20KHz)

Filter Type . . . . . . . . . . . . . . . . Constant Q/Wein Bridge

Bandwidth . . . . . . . . . . . . . . . . 2/3 octave

Tolerance . . . . . . . . . . . . . . . . . ±3%

Range . . . . . . . . . . . . . . . . . . . . ±6 or ±15dB

Subsonic Filter . . . . . . . . . . . . 18dB/octave @20Hz

Compressor/Limiter:

Gain:
Ratio:

Attack Time: . . . . . . . . . . . .

Release Time: . . . . . . . . . . .

Output:

Maximum Input Level: . . . .

Maximum Output Level: . .

Input Impedance: . . . . . . . .

Output Impedance: . . . . . . .

Frequency Response: . . . . .

Distortion: . . . . . . . . . . . . . .

Output Hum and Noise: . . .

. . . . . . . . . . . . . . . . . . ±15dB

. . . . . . . . . . . . . . . . . . 2:1 →

. . . . . . . . . . . . . . . . . . -∞ to +18dB

∞

200µS-20mS
100mS-3Sec

+23dBu
+23dBu
20KΩ balanced
200Ω

Pseudo-Balanced
±0.2dB 20Hz-20KHz
<.01% THD, 0dBu, 1KHz
<0.15% THD, +15dBu,
20Hz-20KHz
<-95dBu

Serial Number ______________________________

Dealer _____________________________________

Date of Purchase____________________________

13. SPECIFICATIONS

EQ:

Input Type . . . . . . . . . . . . . . . . Active Balanced

Impedance . . . . . . . . . . . . . . . . 20KΩ Balanced

10KΩ Unbalanced

Max. Level . . . . . . . . . . . . . . . . +23dBu

Input Connectors . . . . . . . . . . 1/4" Phone Jack, XLR

Output Type . . . . . . . . . . . . . . . Pseudo-Balanced

Impedance . . . . . . . . . . . . . . . . 200Ω Balanced

100Ω Unbalanced

DPX-100 Power Requirements:

93VAC-120VAC, 50-60Hz, 10W

Size and Shipping Weight:

19"L x 1.75"H x 6"D (8 lbs.)

Note: 0dBu = 0.775 Vrms

Pseudo-Balanced Output has balanced output impedance
with single ended signal.

15

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

14. DIMENSIONS

17.00

6.00

0.10

0.75"

1.25

1.75

Dimensional Drawing for DPX-100

16

7654321

y

8

15. SCHEMATICS

17

E

J1

D

47P3151

J8

47P1295

BALANCED
INPUT

C

J4

B

47P3151

J9

47P1295

BALANCED
INPUT

FILTERS
10s1551c-2.SCH

A

TIP = INPUT
RING = SEND

R11
68

+18

7

V+
V-

GND

Ec+

5

6

2

R12

4.7K

-18

C3

27P

4560

R6 10.0K

C2

1N4148

PEAK BUS 1

D1
1N4148

INPUT METER

R9
22K

U2B

7

4560

U1B

VR7

7

50K

SYMMETRY

27P

ADJUST

D53

R10

1 8

15K

+18

R14
300K

-18

PEAK BUS 1

SW5A

2

45P2000

3

U18

52P2150

4

IN

Ec-

Ec+

R13
68

1
3

GAIN +/- 15db

VR1
B10K

R8

SW5B

C64

5

45P2000

47U

2

3

1

4.7K

R7

4
6

IN

6

22K

5

R3

5

10.0K

6

R4

10.0K

C1

R5

27P

10.0K

DETECTOR

J3

47P3151

R15

15K
C4
27P

U2A

2

4560

3

C65

1

47U

C68
47U

VR6
B10K

R35

10K

OUTPUT

(+17.0db MAX)

VR2
B100K

C66

U1A

3

1

4560

2

R20
100K

R16
1K

R34
10K

R36
820

47U

C6

D6

27P

R37 12K

1N4148

C69

6

U5B

7

4560

5

47U

R17

R19

9.76K

100K

THRESHOLD

(-20db MIN +41.4db MAX)

PEAK BUS 1

OUTPUT METER

R2
100

R1

R38

100

10K

R18
1M

6
5

OUTPUT

4560

J6

2

3

1

47P1030

C5

5pF

U3B

J2

47P3151

VR3
A10K

2
3

RELEASE

VR4

A1MEG

C79

1.5U
C80

1.5U

U4A

4560

R29

R33

100K

1K

GAIN METER

R30

R32

68K

1K

R31

3.3K

Q6

1

2N4123

+18

R25

C6747U

7

R26
10K

R27
10K

1N4148

2

U3A

4560

3

R21
10K

R22 4.99K

1N4148

1

1N4148

D4

D2

D3

150K
R23

3.3K
R24
47K

D15

1N0754

6
5

LIMIT

3

ATTACK

SW1A

2

1

D5

OUT

45P2600

-18

1N4148

U4B

7

4560

THRES

-18

R28
100

Q1
2N4125

RATIO

VR5
C10K

COMPRESSOR/LIMITER

CASCADE

C74

HPF

OUT

47U

SW8A

1

45P2600

D7

PEAK BUS 2

1N4148

SIG

R39
R40

2

3

1

PWR SUPPLY + METERS

TO EVEN
TO ODD

T1
T2
T3

10s1551c-3.SCH

1 2 3 4 5 6 78

10.0K

10.0K

C7
27P

PEAK BUS 1
PEAK BUS 2
THRES
SIG
INPUT METER
OUTPUT METER
GAIN METER

R41

10.0K

3
2

U6A

4560

R42

10.0K
C8

27P

C70

1

47U

REVISION HISTORY
10s1551RV.SCH

C9

.1U
R43
10K

R49
22K

C10

C11

.1U

.1U
R47
62K

20 Hz HPF 18dB
/OCT.

6

U23B

7

4560

5

R48
470K

2

3

7

R50

7

J20/2G

JP16/2

C72

JP16

47U

R51
20K

-18-18

J20/2C

3

J20/2D

4

+18

J20/2E

5

FILTER BOARD

(ALONG WITH SHEET 2)

J20/2B

2

EQ GAIN

15K

PEAK BUS FLTRPEAK BUS 2

JP17/2

VR8

JP18/2

JP18

R53

JP17

10K

R52
30K

C12

27P

U7B

6

7

2043

5

2
3

J20G

J20C

3

J20D

4

+18

J20E

5

J20B

2

JP21

C13 27P

6
5

D9

PEAK BUS FLTR

R65

2.55K
R66

8.2K

U9A

4560

R5820K

JP21/2

T1

R60
10K
U8B

R54

7

2043

10K

R63
10K

RANGE SWITCH

IN +/- 6 dB
OUT +/- 15 dB

SW2B
45P2600

OUT OUT

4

5

6

1

TO ODD

2
3

C14 27P

R61
10K

U8A

2043

T2 T3

1

R67

2.55K
R68

8.2K

6
5

EQ SWITCH

R17610K

U6B

6

7

5

4560

R45
100

C71

R46

47U

10K

Phone: Fax:

[phone]

Drawn B

James B Franks

EQ

OUTPUT

J7

3

47P1030

R44
100

C

$VKO\ $XGLR ,QF

847 Holt Road
Webster, NY 14580-9103

[phone]

Print Date

3-May-2002

10S1551

11:44:50

2
1

47P3151

J5

Rev.

C

JP20JP19 JP20/2JP19/2

C15 27P

R62
10K

R55

2

10K

3

R64
10K

SW2A
45P2600

2

U9B

7

4560

C73

U7A

1

2043

47u
D8
1N4148

PEAK BUS FLTR

1
3

TO EVEN

R57
390K

OUT

SW3B

4

45P2600

5

6

1

J20A

J20/2A

1

R56
20K

Size

B

DPX-100 MINI-EQ + COMPRESSOR/LIMITER

APPROVED: Dwg #

U23A

2
3

4560

1

A->B @ 157%

R177
10K

C16

R59

.1U

2.2M

Sheet # of

14

S:\Engineering\CLIENT98\1551\10s1551c-1.Sch

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

E

D

C

B

A

18

y

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

7654321

C17

.1u

R71

C18

E

D

C

B

A

TO ODD

.1u

C20

TO ODD

.1u

C22

TO ODD

.01u

C24

TO ODD

.01u

1 2 3 4 5 6 78

63.4K

R70

U10B

6

R69

63.4K

R75

9.76K

R80

15.8K

R85

2.55K

7

4560

5

4.7K

R72

7.87K

R73

10.0K

25 Hz 40 Hz 63 Hz 100 Hz

C19

.1u

R76

9.76K
U12B

6

4560

5

R77

7.87K

R78

10.0K

C21

.01u

R81

15.8K
U14B

6

4560

5

R82

7.87K

R83

10.0K

C23

.01u

R86

2.55K

6

U16B

4560

5

R87

7.87K

R88

10.0K

6.3 KHz 10 KHz

JP29

R74

7

4.7K

160 Hz 250 Hz

JP33

R79

7

4.7K

1 KHz 1.6 KHz

R84

7

4.7K

T2

JP25

JP37

VR9

JP25/2

T1

T2

VR13

3

4

1

JP29/2

2

T1

T2

VR17

JP33/2

T1

T2

VR21

JP37/2

T1

TO EVEN

TO EVEN

TO EVEN

TO EVEN

C26

.1u

C28

.01u

C30

.01u

C32

.01u

R90

39.2K

R95

63.4K

R100

9.76K

R105

1.58K

C25

.1u

R91

39.2K
U10A

2

4560

3

R92

7.87K

R93

10.0K

C27

.01u

R96

63.4K
U12A

2

4560

3

R97

7.87K

R98

10.0K

C29

.01u

R101

9.76K
U14A

2

4560

3

R102

7.87K

R103

10.0K

C31

.01u

R106

1.58K
U16A

2

4560

3

R107

7.87K

R108

10.0K

JP26

R89

1

4.7K

JP30

R94

1

4.7K

JP34

R99

1

4.7K

JP38

R104

1

4.7K

T3

VR10

JP26/2

T2

T3

VR14

JP30/2

T2

T3

VR18

JP34/2

T2

T3

VR22

JP38/2

T2

TO ODD

TO ODD

TO ODD

TO ODD

C34

.1u

C36

.01u

C38

.01u

C40

.01u

R110

25.5K

R115

39.2K

R120

6.34K

R125
976

C33

.1u

R111

25.5K
U11B

6

4560

5

R112

7.87K

R113

10.0K

C35

.01u

R116

39.2K
U13B

6

4560

5

R117

7.87K

R118

10.0K

C37

.01u

R121

6.34K
U15B

6

4560

5

R122

7.87K

R123

10.0K

C39

.01u

R126
976

6

U17B

4560

5

R127

7.87K

R128

10.0K

JP27

R109

7

4.7K

JP31

R114

7

4.7K

400 Hz 630 Hz

JP35

R119

7

4.7K

2.5 KHz 4 KHz

JP39

R124

7

4.7K

16 KHz

T2

VR11

JP27/2

T1

T2

VR15

JP31/2

T1

T2

VR19

JP35/2

T1

T2

VR23

3

4

1

JP39/2

2

T1

C42

TO EVEN

TO EVEN

TO EVEN

R130

15.8K

.1u

C44

R135

25.5K

.01u

C46

R140

3.92K

.01u

Size

Sheet # of

B

S:\Engineering\CLIENT98\1551\10s1551c-2.SCH

DPX-100 MINI-EQ + COMPRESSOR/LIMITER

APPROVED: Dwg #

C41

.1u

R131

15.8K
U11A

2

4560

3

R132

7.87K

R133

10.0K

C43

.01u

R136

25.5K

2

U13A

4560

3

R137

7.87K

R138

10.0K

C45

.01u

R141

3.92K
U15A

2

4560

3

R142

7.87K

R143

10.0K

24

R129

1

4.7K

R134

1

4.7K

R139

1

4.7K

A->B @ 157%

2

3

JP28

JP28/2

JP32

JP32/2

JP36

JP36/2

U17A

1

4560

T3

VR12

T2

T3

VR16

T2

T3

VR20

T2

Phone: Fax:

[phone]

Drawn B

James B Franks

8

JP24

JP24/2

TO EVEN
TO ODD
T1
T2
T3

C

$VKO\ $XGLR ,QF

847 Holt Road
Webster, NY 14580-9103

[phone]

11:43:56

Print Date

3-May-2002

10S1551

E

D

C

B

Rev.

A

C

7654321

y

8

19

E

D

C

B

A

OUTPUT LEVEL (db)

SW1B
45P2600

5

6

+18

D38

+18

R159
15K

R158

THRES

+18

R147

1.5K

D26
LIMITER(G)

4

OUT

D27
POWER(Y)

2N4125
Q3

560

D14
1N4148

C84

1.5U

-18 -18

GAIN METER

D13
1N4148

C76
47U

R160
100K

J14/2A

J14A

J14/2B

J14B

J14/2C

J14C
J14D

J14/2D

J14/2E

J14E
J14F

J14/2F
J14/2G

J14G

J14/2H

J14H

GAIN REDUCTION (db)

+18

D49

D39

-2(R)

(Y)
R161

1.5K

Q9
2N4123

+18+18

-18-18

-18

D48

-16(R)

-14(R)

-12(R)

-10(R)

-8(R)

-6(R)

-4(R)

18

-20(R)

-18(R)

10

U22
LM3914

LED911LED812LED713LED614LED515LED416LED317LED2

LED10

PEAK BUS 1

LM3914

SIG IN5MODE

RLO4RHI6REF ADJ

V+3V-2REF OUT

R162

4.7K

D18
1N964
13V

LED1

9

8

7

1

R163

R164

4.7K

+18

2K

Q7
2N4123

R148

R149

390K

2.4K
C52

.1U

R157
100K

Q8
2N4123

R150
62K

R155

R156
100K

1K

D11

D12
1N4148

1N4148

-18

U5A

2

1

3

4560

8 4

+18-2

C83

1.5U

INPUT METER

OUTPUT METER

-18
+18 +18

D40

D41

D42

D43

D44

D45

D46

D47

R151

1.5K

-21(G)

D28
+20(R)

METER SELECT

J13/2A

J13A

J13/2B

J13B

J13/2C

J13C

J13/2D

J13D

J13/2E

J13E
J13F
J13G
J13H

-18

J13/2F
J13/2G
J13/2H

3
1

-18

-18(G)

SW4A
45P2600

OUT

R152

4.7K

D37

D17
1N964

D35

D36

-15(G)

-12(G)

2

D34

-9(G)

18

LED1

1

D32

D33

-3(G)

-6(G)

LM3915

SIG IN5MODE

RLO4RHI6REF ADJ

V+3V-2REF OUT

7

+18

R153

2.4K

D29

D30

D31

+3(Y)

0(Y)

+6(Y)

10

U21
LM3915

LED911LED812LED713LED614LED515LED416LED317LED2

LED10

9

8

R154

2.4K

COMPRESSOR/LIMITER METERS

+18

R165

1.5K

Q11
2N4123

D50
CLIP(R)

+19 dBu

Q10

2N4123

R166
62K

SIG

EQ METERS

Size

Sheet # of

34

B

S:\Engineering\CLIENT98\1551\10s1551c-3.SCH

DPX-100 MINI-EQ + COMPRESSOR/LIMITER

APPROVED: Dwg #

A->B @ 157%

D52

1N4003

In

In

1N4003

+18

D16
1N754

VCC +

FOR IC 5

Q2
2N4125

C50

+18-2

220P

D10

C51

1N270

.1U

D25
1N4003

D24
1N4003

+18

C49

C53

C55

.1U

.1U

C48

C54

.1U

.1U

-18

C57

.1U

.1U

C56

C58

.1U

.1U

3

C81

1.5u

C82

1.5u

3

PEAK BUS 2

C59

C61

.1U

.1U

C60

C62

.1U

.1U

R167

R168

390K

2.4K
C63

.1U

R145
10K

R146

3.3K

Out

2

1

Out

PEAK BUS 1
PEAK BUS 2
THRES

SIG
GAIN METER
INPUT METER
OUTPUT METER

1

D20

1N4003

D22

1N4003

C85
1000u

C86
1000u

U19

7818

U20
7918

2

D23

C47
.1U 100V

R144

1.5K

D19

1N4003

D21

1N4003

J19
KEYSTONE

T1

2 11

J10

L
G
N

47P1413

J11

J21

KEYSTONE

KEYSTONE

1 2 3 4 5 6 78

F1

1/2 AGC

J12

KEYSTONE

SW6

45P1501

out

J15
KEYSTONE

out

110VAC 220VAC

J16
KEYSTONE

SW7

45P1501

3 10
4

5

J17
KEYSTONE

51P7308

8

J18
KEYSTONE

+18

R169

R173

63.4K

19.6K

C78
47U

Q12
2N4123

R170

3.92K

R17168R172

1.58K

-18

C

$VKO\ $XGLR ,QF

847 Holt Road
Webster, NY 14580-9103

Phone: Fax:

[phone]

Drawn B

James B Franks

C77
47U

Q5
2N4125

[phone]

Print Date

3-May-2002

10S1551

Q4
2N4125

R174

1.5K

11:42:28

D51
SIG(G)

-20dBu

Operating Manual - DPX-100 Graphic Equalizer - Compressor/Limiter

E

D

C

B

Rev.

A

C

Operating Manual - DPX-100 Gr aphic Equalizer - Compressor/Limiter

ASHLY AUDIO INC. 847 Holt Road Webster, NY 14580-9103

Phone: [phone] Fax: [phone]

Toll Free [phone] Internet: www.ashly.com

 2002 by Ashly Audio Corporation. All rights reser ved worldwide.

Printed in USA 05/02 DPX100 -0