Meyer M-1A Operating Instructions Manual

Meyer Sound Laboratories, Inc.

2832 San Pablo Avenue

Berkeley, CA 94702

Operating Instructions

M-1A
Control
Electronics
Unit

The Meyer Sound M-1A is
an active signal processor
designed for use with Meyer
Sound UPA-1C and UM-1C
loudspeakers. lt is a single
channel device, and it
occupies a single 13⁄4-inch
rack space. The functions
of the M-1A are:

■ Active crossover for bi­amplication

■ Loudspeaker frequency
response and phase
response alignment

■ SpeakerSense™ driver
protection

+–

Input

Sub

In

Lo Hi

Sense

Lo

Out

Hi

Out

1/4 A

Hi Channel

+–

Lo Channel

Amplifier

Loudspeaker Cable

Input

1 Meter

Pigtail

Adapter

Red

Sense

Cable

Red

Black
Sense
Cable

Black

Connections

The M-1A operates at line level and is de­signed to be the last component in the chain
before the power amplier. Connections to
the M-1A should be made according to the
diagram above.

1. Signal inputs to the M-1A may be either
balanced or unbalanced. For best sig­nal-to-noise ratio, the average input level
should be at least 1 volt RMS. The M-1A
will accept peak inputs of up to +26 dBv
balanced, or +20 dBv unbalanced.

2. The Sub input is used only when the M­1A is operated in conjunction with Meyer
Sound B-2, B-2A or B-2AEX subwoofer
Controllers.

3. SpeakerSense™ connections are made
from the output of the power amplier
back to the M-1A Sense inputs. The Hi
output of the power amplier must be
connected to the Hi Sense input, and the
Lo output of the power amplier to the Lo
Sense input in order for the SpeakerSense
driver protection circuitry to operate prop­erly.

Note. Polarity of these connections does not
matter.

4. Signal outputs from the M-1A may be
either balanced or unbalanced. The max­imum output levels before clipping are
+26 dBv balanced, +20 dBv unbalanced.

5. Connections between the power amplier
outputs and the Meyer Sound loudspeaker
used with the M-1A should be made ac­cording to the instructions for the particular
loudspeaker (UPA-1C or UM-1C). These
connections must be veried for correct
polarity, and correct channel assignment
(Hi to Hi, Lo to Lo). Color codes given
in the diagram are those used for Meyer
Sound cables and adapters.

Note. The grounding strap on the M-1A rear
panel connects circuit ground (signal com­mon) to earth ground (U-ground). Lifting this
strap from the terminal block disconnects
circuit ground from earth ground (the chas­sis remains connected to U-ground). If hum
problems occur, this feature may be used to
control ground loops in the system.

Operating Instructions

Meyer Sound Laboratories, Inc.

2832 San Pablo Avenue

Berkeley, CA 94702

M-1A
Control
Electronics
Unit

Meyer Sound Laboratories, Inc.

2832 San Pablo Avenue

Berkeley, CA 94702

Operating Instructions

M-1A
Control
Electronics
Unit

Once all the connections have been made
and veried, the system is ready to operate.

■ The M-1A Level control should be set at
minimum.

■ Switch on AC to the M-1A rst, then to the
power amplier.

■ Set the power amplier level controls (if
any) to maximum.

■ Advance the M-1A Level control to set the
system sensitivity. If the system is not op­erating properly, recheck all connections.

Operation

Preset Panel Controls

The setup controls on the M-1A Preset Panel
are designed to be used to tailor the system
response for particular applications. Remove
the Preset Panel cover plate to adjust the
controls.

Safe Switch. The M-1A incorporates three
limiters in the SpeakerSense driver protec­tion circuitry (see detailed description, below).
When the Safe switch is engaged, the RMS
limiters come on at 6 dB lower power lev­els, affording added protection when heavy
continuous power demands are placed on
the system. (The VHF peak limiter threshold
is unaffected.) For operator convenience, a
green LED indicator is provided on the M-1A
front panel and when the Safe switch is en­gaged, this indicator will light. Note: It is rec­ommended that the Safe switch be engaged
until the operator is familiar with the system’s
capabilities.

VHF Switch and Control. The VHF Switch
affects the very high frequency response of
the system. It selects either a preset (CAL)

high frequency response or variable response
(VAR). In the VAR position, system response
around 16 kHz is adjustable (single-turn
screwdriver adjustment) from +6 dB to -4 dB
around the preset point (CCW for increased
level at 16 kHz). This feature may be used
to emphasize or de-emphasize sibilants,
compensate for room acoustics, etc. Note:
Because of the difference in high frequency
directivity patterns between the UPA-1C end
the UM-1C UltraMonitor, it is recommended
that the VHF switch be set in the CAL position
for the UM-1C UltraMonitor, and in the VAR
position — with the VAR control fully CCW
— for the UPA-1C.

Lo Cut Switch. This switch introduces a
6 dB/octave high pass lter at 160 Hz. It is
designed to provide an alternative crossover
slope when using Meyer Sound subwoofers,
but can also be used to compensate for the
proximity effect of cardioid microphones. This
lter is automatically inserted when the Sub
Input is used.

SpeakerSense™
Driver Protection

Through the Sense connections back to the
M-1A from the power ampliers, the Speak­erSense circuitry of the M-1A continuously
monitors the voltages across both high and
low frequency drivers. If the amplier output
exceeds the safe operating limits of the driv­ers, independent limiters are automatically
activated, holding down the level of the M­1A’s outputs.

The operation of the SpeakerSense circuitry is
indicated by a set of ve LEDs located on the
front panel.

■ Sense Indicators. These function as sig-
nal presence indicators, and verify that the

Sense connections back to the M-1A are
made. These indicators will be lit whenever
a signal is present, or will icker at low
signal levels.

■ Limit Indicators. These indicators will
come on whenever the corresponding lim­iter is activated and a moderate amount of
ashing of these indicators is acceptable.
The HF and LF limiters have an attack
time of 100 msec, so they will not affect
peaks in the program material, nor will they
prevent momentary amplier clipping on
peaks.

Meyer Sound Laboratories, Inc.

2832 San Pablo Avenue

Berkeley, CA 94702

Operating Instructions

M-1A
Control
Electronics
Unit

Verifying Limiter
Operation

To verify limiter operation in the eld:

■ Disconnect loudspeakers, leaving the
amplier and the M-1A in their standard
connection conguration.

■ If your amplier requires a load, use re­sistive loads sufcient to dissipate the full
power of the amplier.

■ Turn on both the M-1A and the amplier.

■ Set the VHF switch to CAL, the Lo Cut out

and the Safe switch in.

■ Supply an input to the M-1A, preferably a
sine wave oscillator. If you do not have an

oscillator, use a compact disc with dense
program material and a mixer to produce a
line level signal.

If you are using an oscillator, set the fre­quency according to this table:

LF limiter HF limiter VHF limiter

200 Hz 5,000 Hz 16,000 Hz

Bring up the input level until you see the cor­responding limit indicator come on. Since in
each case the indicator will light only if the
limiter actually operates, it provides a positive
indication that the limiter is functioning.

Balancing Amplier
Gain

The standard connection conguration for the
M-1A Control Electronics Unit uses a single
two-channel amplier as a bi-amplier, one
channel for the lows and one for the highs.
In large systems where a number of M-1As
are used, some users prefer to assign one or
more ampliers only to the lows, and other
ampliers only to the highs. In either case the
Lo and Hi ampliers must have equal voltage
gain. To balance your system, you will need
an oscillator and an RMS-reading voltmeter.

■ Connect the M-1A and ampliers as you
wish to use them, leaving speakers discon­nected.

■ If an amplier requires a load, use an
8 ohm resistor sufcient to dissipate the
full power of the amplier.

■ Input the oscillator to the M-1A and set its
frequency to 1600 Hz ± 5 Hz (use a fre­quency counter if you have one).

■ Set the M-1A Lo Cut switch out, the VHF
switch to CAL, and the Safe switch out.

■ Measuring with the voltmeter at the Hi
amplier output, advance the M-1A Level
control to a convenient reading (a few
volts).

■ Now measure at the Lo amplier output. If
the level is different, adjust the input level
control of whichever amplier is higher
in output until the Hi and Lo outputs are
equal.

The amplier gains are now calibrated.

Using the Sub Input

The Meyer Sound B-2EX Control Electronics
Unit does not incorporate a Hi output, and
is designed to be connected in parallel with
the input of the full-range CEU that it is sup­plementing. If you are using a B-2EX CEU,
do not use the M-1A Sub input. Instead,
connect the system input signal to both the
M-1A Input and the B-2EX Input. For further
information, consult the B-2EX Operating

The M-1A Sub input is designed for use with
the Meyer Sound B-2, B-2A and B-2AEX
subwoofer Control Electronics Units.

If you are using one of these CEUs to control
a subwoofer system that is augmenting the
M-1A system, you have the option of con­necting the subwoofer controller’s Hi output
to the M-1A Sub input. For details, refer to
the Operating Instructions for the subwoofer
CEU.

Operating Instructions

Meyer Sound Laboratories, Inc.

2832 San Pablo Avenue

Berkeley, CA 94702

M-1A
Control
Electronics
Unit

Specications

Balanced (active), 47k ohms

Active push-pull, will drive 600 ohms

+26 dBv
+20 dBv

-90 dBv ("A" weighted)

>110 dB

10k ohm true differential

1600 Hz

Active all-pass

RMS limiter, 100 msec. integration time
RMS limiter, 100 msec. integration time
VHF Peak limiter, 2 msec. on-time, 35 msec.
release time

Green LEDs
Red LEDs
Green LED
Green LEDs

Level control, AC on/off switch
Lo Cut switch, Safe switch, VHF var/cal
switch
VHF control (single-turn screwdriver adjust)

XLR-type (A-3), 1/4" RTS phone receptacles
Unbalanced, 1/4" phone receptacle
(inserts Lo Cut, disables Level control)
Banana receptacles

120V AC
240V AC option available

19"W x 1 3/4" H x 7 3/4" D

8 lbs (3.4 kg)

Input Type

Output Type

Maximum Input/Output Level
Balanced
Unbalanced

Hum and Noise

Dynamic Range

Sense Inputs

Electronic Crossover Frequency

Low Frequency Delay Type

Driver Protection Circuitry
Low Frequency
High Frequency

Indicators
Sense: Hi and Lo
Limit: Hi, Lo and VHF
Safe
Power Supply, Positive and Negative

Controls
Front Panel
Preset Panel

Connectors
Balanced Inputs/Outputs
Subwoofer Circuit Input

Sense Inputs

Power

Physical Dimensions

Weight

05.050.041.01A

© 1994 Meyer Sound