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.