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AM3044 Module - 24dB Low Pass Filter
Overview This module
is designed around the infamous SSM2044 VCF chip that appeared in a variety of analog synths and drum machines in the early 1980's, including the Korg PolySix, PPG Wave 2.2 and the E-mu SP1200.
A direct descendent of the
legendary SSM2040 chip, and designed by Dave Rossum and Ron Dow in 1980. The design was patented in the USA (4,404,529) and described as a low pass filter circuit, employing feedback current mirrors as dynamic resistive elements,
and characterized by high accuracy, low noise, and low distortion. Whatever the specification, its a very nice and fat low pass filter!
AM Circuit The AM3044 module is based around the original datasheet and an
article that appeared in Polphony magazine in 1982. The Q of the SSM2044 can be voltage controlled, but it behaves reverse exponentially, as the chip was designed with micro-processor control in mind (polyphonic synths).
When
used as a stand alone module a reverse audio control voltage is needed to give a sensible control pot "feel". The Polyphony article by Tom Heifrich uses a CA3080 to provide this reverse log control. However I have decided to use AnalogDNA technology to achieve a more accurate result and without the need for an obsolete chip.
The filter can be built without the 1K 3600ppm Tempco resistor, but the oscillation at high Q settings will not track properly.
Panel The front panel is a standard AM design with 3mm aluminium, 4U high,
with light blue lettering.
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