Ashly FET-200 User Manual

ASHLY

MOS-FET POWER AMPLFIERS

OPERATING INSTRUCTIONS

ASHLY AUDIO INC.

1. Introduction

TABLE OF CONTENTS

Page

2. Unpacking, Installation

3. Input & Output Connections, Stereo Operation

4. Mono Operation

5. Bridging Operation

6. Meter Display

7. Thermal Status Indicator

8. Specifications/Block Diagram

9. Definition of Terms

4

5

7

7

8

8

8

9

INTRODUCTION

The Ashiy FEX-200 and FEI-500 represent an entirely new breed of power
amplifiers which are destined to replace conventional amps in virtually every
application. Far from being just'another variation on well worn designs, these
amplifiers have been engineered from the ground up to take full advantage of
an exciting new semiconductor technology which has recently become

availabie—the Power HOS-FET (metai-oxide-semiconductor, field-effect-

trausistor). Combining many of the desireable operating characteristics of

vacuum tubes with the efficiency of transistors, the MOS-FET offers superior

audio fidelity and introduces an entirely new level of field reliability.

Ashiy power amplifiers put all of these features together into a carefully

thought out, roadworthy, user-oriented package which will provide years of

maintenance-free service.

WHY MUb-F£X’3?

Conventiouai power amplifier design as typically produced a circuit which

consists of two parts; 1) the amplifier itself, and 2) a collection of

protective circuits which keep the amplifier from destroying itself and the

speakers it is driving. Some of the more common protective circuits include
\?I limiting, Liiermai feedback, detectors that monitor DC at the output

terminals, short circuit protection and turn-on delay circuits that keep the
speaxers from jumping out of their cabinets when power is applied. The result
has typically been a compromise in audio performance, greatly compounded
electronic and mechanical complexity, and amplifiers which are intolerant of

less than ideal operating environments.

The basic vveakness of these amplifiers has always been the power output

transistors themselves, which are prone to failure as a result of "thermal

runaway”. This breakdown occurs when the amplifier is delivering a lot of

power and begins to heat up. Increasing temperature produces an increase in
collector current in the output transistors, whicli in turn produces more heat.

If this cycle is unchecked, the transistor will be destroyed.

ProoaDiy cue greatest advantage of power NOS-FET's for professional audio use

is their complete immunity to thermal runaway. Not only does this remove the
primary failure mechanism of the conventional amplifier and eliminate the need
for elaborate thermal protection circuits, it also allows the design engineer

to use a much Higher quiescent current in the amplifier's output stage,

thereby insuring that the output devices are always operating in their most

linear region. This results in consistently lower distortion.

In addition, the simpler input drive requirements of the MOS-FET devices makes

possible a clean, concise amplifier design. The resulting reduction in

component count and internal wiring provides for a compact design and enhanced

reliability.

THE ASHLY DESIGN

Our goal in designing the FET-200 and FET-500 was to produce amplifiers that

combine the sonic excellence of a high-end stereo amp with the ruggedness and

stamina necessary in pro audio.

ELECTRONIC

Both amplifiers are fully complementary, push-pull type with totally discreet,
high voltage, wide bandwidth electronics. This approach inherently assures
low noise, low distortion, and excellent transient response. Inputs are
bringing, active balanced (transformerless), equipped with both 1/4" jacks and
XLR-type connectors of both sexes to facilitate linking several amplifiers

together. All input connections can, however, operate as balanced or

unbalanced. This is determined by the connector used in conjunction with the

input. Stereo, mono and bridging modes are user selectable by means of rear

panel switches, requiring no internal modifications or additional components.

All electronic components are conservatively rated and are mounted on a rugged
glass-epoxy circuit board. An efficient U-I laminated power transformer saves

space and minimizes magnetic flux leakage, permitting other low-level

equipment to be mounted above or below the amplifier with no danger of induced

hum. Large value, computer grade electrolytic capacitors assure long service.
Two lU-segment, 27 dB range LED meter displays provide an easily viewed
indication of power levels, and a separate LED indicates thermal overload.

HECIL\NICAL

Ihe Ashly MOb-FET power amplifiers are packaged in a rugged, one-piece welded

16 gauge steel chassis with an anodized aluminum front panel and an easily
removed steel top cover. The chassis and ail internal components are

integrated into a single, rigid unit. The FET-500 requires 5 1/4" of rack

space and the FET-200 requires only 3 1/2". The power transformer is located
near the front of each amplifier, reducing mechanical stress on the chassis.
Each channel's electronics and heat sink are combined into a compact, plug in
module which can be removed from the amplifier in seconds. Hard wiring is at
an absolute minimum.

Large heat sinks and an aerodynamic internal design permit the use of an
ultra-quiet, slow speed fan which pulls air in through the front panel
directly across the heat sinks and power transformer, and out through the rear

panel. It is unnecessary to provide space or ventilation above or below the

amplifier, allowing for economical use of rack space.

The amplifier's output connectors are conveniently arranged on standard 3/4"

spacing tor quick interconnect via banana plugs. Selecting the bridging output

involves only moving the banana plug to the two center (RED) connectors. Both
the AC line and the speaker terminals are fused protected. Fuses can be
removed instantly without tools. There are no internal fuses.

IN USE

The result: better sounding amplifiers, remarkably un-fussy about how you use

them. They will tolerate low impedance, highly reactive loads and hot,
crowded racks. They are highly immune to RF interference and will not be
damaged by intermittent short circuits—sustained shorts will simply blow the

output fuse. Due to their balanced circuit design, the use of delay circuits

and output relays are unnecessary. There is no turn-on thump and the volume
controls can remain up when power is applied and removed. Both amps will keep
on running right through a brown-out, even when line voltages fall to as low

as 20 volts!

This manual will explain the proper installation and use of Ashly amplifiers
and their controls. Please read it carefully and refer to it in case of

difficulty.

UNPACKING

As part of our system of quality control, every Ashly product is carefully

inspected before leaving the factory to ensure flawless appearance. After un
packing please inspect for any physical damage. dave the shipping carton and
all packing materials, as they were carefully designed to reduce to a 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 aamages 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 PACKING
MATERIALS UNTIL THE CLAIM HAS BEEN SETTLED.

INSTALLATION

Ashly MOS-FET amplifiers are designed to mount in a standard ly" equipiacnt

rack. Since forced-air cooling is employed, it is not necessary to leave any

ventiiation space above or below the amplifier. This permits efficient use of

rack space and multiple stacking of amplifiers. The only precaution to

observe is to leave the front panel air inlets and rear panel fan outlet

unobstructed.

The use of four front panel screws is recommended to evenly distribute the

stress on the panel. The amplifier chassis is sufficiently strong to support

itself by the front panel alone in permanent installations or where the rack

is moved only occasionally. For amplifiers which will spend much of their
time in transit, it is suggested that some method of rear support be used.

Connect all amplifiers to a 3-wire grounded outlet supplying 120 Volts 50-60Hz

Maximum power consumption is 600 watts. Maximum current required is 5 amps.

INPUT AND OUTPUT CONNECTIONS

STEREO OPERATION

Connections for stereo operation are shown in figure 4 below.

Figure 4 Stereo Operation

INPUTS

The input of Asnly amplifiers is a balanced bridging type, with an input
impedance of 10k ohms. Use of the balanced input provides superior hum and
noise rejection while eliminating ground loops. The input may also be used in

a single-ended, unbalanced mode by simply using unbalanced input connectors.

Each channel provides a choice of either 1/4” jacks or XLR input connectors.
All four connectors are in parallel. Since only one of the four connectors is
used as an input at any one time, the others may be used to jumper other
amplifiers to the same source.

Signal connections are as follows:

The (+) or in-phase connection is on the tip of the 1/4" stereo phone jacks,
and is on pin 3 of the XLR connectors. The (-) or out-of-phase connection is
on the ring of the phone jacks and on pin 2 of the XLR's. Chassis ground and

shield is on the sleeve of the 1/4" jacks and pin 1 of the XLR's.

Shield (Sleeve)

\

Shield

Figure 5

When feeding the amplifier from an unbalanced source, use either an XLk
connector or a standard stereo 1/4” phone plug and connect the signal "hot"
connection to XLR pin 3 or to the phone plug tip. Connect signal ground to

the XLR's pins 1 and 2 or to the phone plug's ring and sleeve. The latter may

also be accomplished by simply inserting a standard 1/4” mono phone piug,

which automatically connects ring and sleeve together.

In the special case where the amplifier is physically mounted in tiie same rack
with the signal source that is feeding it, you may wish to use an alternate
connection system to avoid ground loops: connect the signal hot to XLR pin 3
or to the phone plug tip. Connect signal ground to XLR pin 2 or to the phone
plug ring. Leave the XLR's pin 1 and the jack sleeve unconnected.

SPEAKER OUTPUTS

The speaker output connections are combination banana jacks/binding posts

spaced on standard 3/4" centers. Speaker connections may be accomplishec

either by inserting banana plugs or by feeding bare stranded wire into tue
binding posts.

Figure 6

MONO OPERATION

With the MONO switch depressed, the Channel 1 input will feed both sides of

the amp. Volume for both sides is controlled with the channel 1 LEVEL control.

MIXING

CONSOLE

Figure 7 Mono Operation

BRIDGING OPERATION

Asnly amplxfiers are in tue bridging mode when both the MONO switch and

BRIDGING switch are depressed. In this mode, the channel one input feeds both
sides of the amp, but the phase of the channel two amplifier is inverted 180

degrees, so that the two amplifiers' outputs are out of phase. The speaker
connection is then made to the two RED output jacks, as shown in Figure 8.
The black output jacks are not used.

R L

^OUTPUTS--

MIXING

CONSOLE

Figure 8 Bridging Mode

METERS

The meters on the front panel respond to the peak output voltage of the
amplifier as measured at the speaker terminals. A ten segment, three color

LED display covers a twenty-seven decibel range.

If all of the LED’s on one channel light up and stay on with only a small
input signal, a blown speaker fuse or faulty speaker wiring is indicated.

THERMAL STATUS INDICATOR

In the event that the amplifier overneats, it will automatically shut down and
the green THERMAL STATUS LED will turn off. The fan will continue to run, and.
vdien the heat sink temperature returns to normal the green THERMAL STATUS LED

will come back on and the amplifier will turn itself back on.

It is extremely unlikely that any combination of musical program material and
load conditions will activate the thermal shutoff mechanism in normal use.
Should overheating occur, check to be sure that the air flow in front of and

behind the amplifier has not been blocked.

Note that there is a very generous safety margin between the temperature

required to activate the thermal cutouts and temperatures which could damage
components in the amplifier.

SPECIFICATIONS:

FET-200

RATED POWER 100 Wotts/channel

FET-500

RATED POWER 250Woits/channei

Both channels driven into
8 ohms

160 Wotts/chonnei
Both channels driven into
4 ohms

320 Watts into 8 ohms bridged
mono

Both channels driven into
8 ohms

400Wdtts/channel

Both channels driven into
4 ohms

SOOWotts into 8 ohms bridged

mono

ffiEQUENCY RESPONSE ±.Sdb lOHz-SOKHz

HARMONIC DISTORTION < .05% 20Hz-20kHz, 100 watts,

8 Ohms

IM DISTORTION (SMPTE) < .01% 100 watts, 8 ohms

DAMPING FACTOR > 100 20Hz-20kHz

SLEW RATE: 50V/ fxsec

RISE TIME 2 lisec 10%-90%

FREQUENCY RESPONSE ±.5db 10Hz-50kHz

HARMONIC DISTORTION < .05% 20Hz-20kHz, 100 watts,

8 Ohms

IM DISTORTION (SMPTE) < .01% 100 watts, 8 ohms

DAMPING FACTOR > 100 20Hz-20kHz

SLEW RATE: 50V/ (isec

RISE TIME 2 (isec 10%-90%

ACTIVE

Electronic circuits which use devices such as transistors and integrated
circuits, and which are capable of voltage and power gain as well as
loss. Circuits using only resistors, capacitors, transformers, etc., are
referred to as passive.

AMPLITUDE

The voltage level of a signal. May be measured in volts or decibels.
Generally corresponds to the volume or intensity of an audio signal.

BALAilCED

A 3-wire circuit arrangement in which two conductors are designated as

signal lines (+ and -), and the third is a shield and chassis ground. The

signal lines are of opposite polarity at any given moment, and are of
equal potential with respect to ground, balanced input amplifiers are
used on ail Ashly SC series products^to improve hum and noise rejection.
Jumpering signal minus (-) to ground provides an unbalanced input.

BREATHING

A usually undesirable fluctuation of background noise resulting from

compressor action. (Also called "Pumping.")

DEFINITION OF TER^iS AS USED IN THIS MANUAL

BUTTERWORTH

The name of a particular filter response shape. The response is

essentially "flat" within the pass-band, is 3dB down at the cutoff

frequency, and continues to attenuate at a constant slope. Also called a

"maximally flat" or "critically damped" filter shape, it is very popular

for crossovers and shelving filters.

CENTER FREQUENCY

The frequency (or pitch) at which a filter is most effective. In a
parametric equalizer, it refers to the frequency where a particular
boost/cut control has maximum effect.

COMPRESSOR

An amplifier wiiich reduces its gain as its input is increased
predetermined "threshold."

DAMPING

A

force which opposes the tendency of a system to oscillate.

dB

A unit by which audio levels can be COMPARED. Often thoroughly
misunderstood are the concepts that decibels represent the level of a

signal compared to some reference level (15 dB cut means a certain level
less than a previous level

be known), and that decibels are a logarithmic unit. Some handy numbers

to remember when dealing with decibels;

----

the absolute level of the signal need not

beyond a

+3 dB = Double Power

+6 dB = Double Amplitude,

Quadruple Power

+10 dB = lOX Power
+20 dB = lOX Amplitude, lOOX Power

dBm

A unit of measurement in decibels wnere 0 dBm = a power level of 1

milliwatt into a 600 ohm load. Originally defined by the telephone

company to measure line levels.

dBV

Decibel Volts, an update of the dBm definition where 0 dBV = ttie same
voltage level as 0 dBm, but with no regard to power or impedance. 0 d3V f

0.775 Volts. This unit is much more appropriate for modern audio
equipment with high impedance inputs and low impedance outputs.

DISTORTION

Generally refers to ANY modification of an audio signal which produces
new frequencies which were not in the original. Examples are harmonic

distortion, where a circuit adds overtones to a fundamental signal, and
intermodulation or IM distortion, where two frequencies beat together to
produce sum and difference frequencies.

EQUALIZATION

Modification of the frequency response of an audio
corrective or enhancement purposes.

FEEDBACK

Generally refers to any process where an output is in some form routed

back, to ail input to establish a loop-. Negative feedback tends to be be

seif stabilizing, while positive feedback causes instability.

system for either

FILTER

A circuit designed to pass some frequencies, but not others. There are

three general categories of filters; High-pass, band-pass, and low-pass.

The high-pass filter passes frequencies above a certain limit, the low-

pass passes frequencies below a limit, and the band-pass passes one group
of frequencies without passing those above or below. Our equalizer uses
band-pass filters, crossovers use high and low-pass filters.

FREQUENCY

The repetition race of a waveform. Frequency is measured in Hertz. One
cycle per second (cps) is one Hertz (Hz). The higher a note on a musical

scale, the higher its frequency.

FREQUENCY RESPONSE

Refers to relative gain and loss at various frequencies across the audio
band. May be illustrated by a graph called a frequency response plot,

usually graphing decibels vs. Hertz or octaves.

HERTZ (Hz)

The unit of frequency measurement,

this explains it perfectly)

HEADROOM

Refers to the increase in level above normal operating level that can be
obtained without clipping. Usually expressed in dB.

(Formerly called Cycles-per-Becond:

10

IMPEDANCE

Essentially the AC equivalent of resistance. It describes the drive
capability of an output, or the amount of drive required for an input at
any given signal level.

KHz

Kilohertz. 1,000 Hertz.

LEVEL

The magnitude of a signal, expressed in decxuels or volts.

LIMITER

An amplifier which reduces its gain as its input is increased beyond a
predetermined threshold. Usually used to protect audio systems against
sudden, high level signals, and possible overload.

Lliffi LEVEL

Meaning "somewhere around OdBV" as opposed to MIC level of around -40dBV.

MILLISECOND

1/lOOOtn of a second

MICROSECOND

1/1,000,000th of a second

OCTAVE

A logarithmic unit to compare frequencies. +1 Octave means double
frequency, -1 Octave means half frequency.

OHM

The unit of electrical resistance or impedance,

PHASE

Describes how well two signals are in step. In-phase means that positive
and negative peaks in two signals occur together, while out-of-phase
means they do not occur together. Variations in signal timing as well as
polarity can make two signals in or out of phase, or anywhere in between.
Phase is usually measured in degrees where 0 degrees is in-phase, 180

degrees is out-of-phase, and 90 degrees is in between (sometimes called
quadrature).

PREAMPLIFIER

The first stage of amplification, designed to boost very low level

signals to line level.

..Q..

A measurement describing the sharpness or broadness of a filter.

PvESONAiiCE

The tendency of an electrical or mechanical system to vibrate (or
oscillate) at a certain frequency.

SATURATION

The point at which the magnetic storage capability of a piece of

recording tape is exceeded.

11

SIBILANCE

The distortion caused by loud high frequency signals, such as the
"Ssss..." sounds in human speech.

SHELVING

Describes an equalization action where all frequencies above or below a
particular frequency are boost or cut.

SLOPE

In a filter or equalizer, a description of the rate of boost or attenua
tion. Usually specified in dB/octave (6, 12, 18, and 24dB/octave slopes

are most common). The steeper the slope, the higher the "Q" in a filter.

THRESHOLD

An arbitrary signal level, above which a limiter or noise gate activates.

TRANSIENT

A sudden burst of energy in an audio signal, such as a breath blast in a
microphone, the sound of a snare drum, or a deep scratch in a record.

Transients frequently reach peak levels of 10 to 30 dB above standard
operating level, and may cause distortion or even damage to equipment.

UNITY GAIN

Output level = Input level.

VGA

Voltage Controlled Amplifier. An amplifier capable of both gain and

loss, controlled by a variable DC voltage.

WIRING, PHONE PLUG AND XLR

A stereo phone plug is wired + to the tip, - to the ring, and shield to

the sleeve. For a mono phone plug, combine - and shield, and connect both

to the sleeve.

An XLR (3 Pin) connector is wired + to pin 3, - to pin 2, and shield to

pin 1.

Sleeve

Mono Phone Plug:

(for unbalanced

Tip

inputs and outputs)

Sleeve Ring

Stereo Phone Plug:

\ /

(for balanced in

puts and outputs)

XLR Type Connector:

(Male Shown)

12

Figure 3