Metro Modular Steel Falcon VCF Sidewinder Edition Instructions And Operating Manual

About the design

Vladimir Kuzmin's 1982-designed Polivoks 2-pole filter
has become a classic reference design thanks to the
sterling efforts of Marc Bareille and The Harvestman,
bringing the idea of a capacitorless programmable-power
opamp filter to a scene fixated on discrete ladders, vac-
trols and OTAs as filter building blocks. However this cir-
cuit technique has not been applied to other filter types
or semiconductors outside of the old LM4250/UA776
chips (or their Soviet equivalents).
Enter the LM346. This chip has been hiding in plain
sight for almost 40 years now and is a much improved
quad version of the LM4250 chip used in many Polivoks
VCF clones . Until now no-one had adapted it to synth
use, despite a datasheet promoting its use in filters.
As the Polivoks was an adaptation of the classic OTA-
based 2-pole State Variable Filter we thought we would
go in the opposite direction and try the 4-pole cascad-
ing lowpass OTA design pioneered by Roland and the
Elektor Formant in the late 1970s. A schematic quickly
sketched in Eagle woorked on breadboard, and the cir-
cuit quickly took shape. Difficulty arose because the
same mechanism that tunes the filter in a programma-
ble power opamp also power-starves the rest of the chip
resulting in some very unpleasant behaviour at the low
end if left unaddressed. A bit of detective work and a bit
of wisdom from the late Bob Pease helped us fix this.
This configuration of the filter was originally designed as
a "playground" configuration to give access to every pos-
sible input and output on the "backpack" filter core cir-
cuit board, in order to work out which features to include
in a more compact version. Reaction was so positive that
we decided to launch the Steel Falcon series with this
version.
The result is a fully featured, rich-sounding lowpass filter
which still has plenty of character and sizzle, and won't
disappoint anyone looking for something new. We hope
you like it like we do!

Specifications and Warranty

40mm flange depth, 60mm internal case depth
recommended as a minimum. 15HP width.
Power requirements:+12V at 35mA, -12V at
35mA for cutoff frequency below 10kHz, rising
to 45mA per rail as cutoff frequency is increased
to maximum. Includes short-term reverse voltage
protection. Connection to higher supply voltages
(such as 15V) may cause the module to exceed
safe operating limits and will void the warranty.
Input impedance (AUD 1, AUD 2, AUD 3):
50kohm unattenuated, 100kohm fully attenu-
ated; logarithmic control response
Input impedance (CRTL 3, CTRL 4): 100kohm
Input impedance (CTRL 1, CTRL 2, LIN FM):
50kohm unattenuated, 100kohm fully attenu-
ated; linear control response
Frequency tuning range: Approx 9 Hz to 22kHz
Resonance: self-oscillation around 3 o'clock posi-
tion on control knob
Output impedance (each output): 1kohm
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, or repair; or exceeding safe operat-
ing limits is not covered by warranty. You MUST
contact us for return authorisation before sending
modules for repair.
MM3461B Manual v1.01
© 2017 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
MM3461B Steel Falcon VCF SE
Instruction and Operating Manual
Metro Modular
"the sound your eyes can follow"