MM315 Balanced Modulator
Instruction and Operating Manual
Metro Modular
“the sound your eyes can follow”
About the design
For the uninitiated, balanced modulation (some-
times called “ring modulation” after an early meth-
od of realising it) differs from a standard Voltage
Controlled Amplifier by allowing negative multipli-
cation of signals as well as positive. It was used in
many classic synths and electronic music studios
to allow the generation of dissonant metallic tones
(not to mention Daleks and Cybermen!) from two
simple input waveforms of differing frequencies.
The MC1496 modulation chip from the late
1960s has passed into legend and is still popu-
lar today, however the original Aries AR315 was
about the only use of its more sophisticated,
much better-performing, analogue computing
grade military spec sibling the MC1595L, which
is now out of production. Unlike the MC1496, the
MC1595L has low distortion and does not “lose
tone” as signal levels are increased.
We started out copying the AR315 design but
performance was poor. Eventually we worked out
that their design was lifted almost wholesale from
the Motorola datasheet (Fig. 21, trainspotters!)
and not only needed to be fully recomputed for
12V supplies, but that a change made by Aries
to facilitate input attenuators had compromised
performance. Adding a high quality op-amp buff-
er allowed these problems to be overcome while
keeping the attenuators! We also restored the Mo-
torola design’s zener-diode-reference subregula-
tors to improve power supply noise immunity and
minimise the need for recalibration.
Lastly, we decided to use old mil-spec LM101AH
or industrial spec LM201AH chips in hermetic
can packages. They did actually sound better!!
Specifications and Warranty
40mm flange depth, 60mm internal case depth
recommended as a minimum.
Power requir12V at 20mA, -12V at
22mA, with short-term reverse voltage protection.
Balanced Modulator section
Inputs protected against pos/neg overvoltage
Input impedance (each channel): 100kohm
Linear control response
Maximum post-attenuator voltage differential
between channels for proper operation: +/-10V
Distortion (10Vpp, 1kHz, X, 50% gain): <0.5%
Output frequency response: DC to 100kHz (-3dB)
Output impedance (each output): 1kohm
Attenuator section
Input impedance (each channel): 100kohm max,
affected by output load and control position.
Linear control response, max +/-20V input.
Patchbay section
is fully normalised
This module is warranted against manufacturing
defects for 12 months from the date of purchase.
Damage or malfunction due to: mistreatment;
mechanical shock; disassembly; unauthorised
modification, calibration or repair; reversed pow-
er supply voltage; or power supply overvoltage is
not covered by warranty. You MUST contact us
for return authorisation before sending modules
for repair.
MM315 Manual v1.01 © 2016 Justin Barrington-Higgs
Check www.metro-modular.com for updated documentation.
Metro Modular is a registered trademark.
Write to us at:
PO Box 3070, Marrickville Metro NSW 2204, Australia
