Yusynth Minimoog Filter
Yves Usson has kindly allowed me to produce a 4U board for his minimoog filter.
This is the classic Moog 4 pole (-24db) low pass filter. Serge never made a 4 pole low pass filter and this is a great addition to my synth.
My circuit is the same as Yves design with the exception of my using 2 TL071 op amps where he uses a single TL072.
My module is built with a Manhattan Analog CP3 mixer
Ladder Filter build notes
Please note that the circuit requires 4 pairs of matched NPN transitors. Many people also match the 4 47n capacitors in the ladder.
Current build is Version 1.0
Download documentation here: Ladder Filter Docs
Yve's documentation for his original design can be found here
Manhattan Analog’s CP3 can be found here
TRIMMING NOTES FROM YVES WEB SITE (edited to match my schematic)
Trimming V/Octave tracking :
Apply 0.000V to the V/Oct input
Turn the frequency knob fully counter-clockwise in order to measure 0mV at the base of Q7 (BC557) (node between R14 to R21)
Apply 1.000V to the V/Oct input
Adjust TR1 (500R) in order to measure 18.2mV at the base of Q1
Apply 5.000V to the V/Oct input Check that you have 91.0mVat the base of Q1, if not adjust TR1
Apply 0.000V to the V/Oct input Set the filter to auto-oscillation (EMPHASIS turned fully clockwise)
Connect a keyboard (CV/GATE) to the V/Oct input Play a tune and check the goodness of the tracking Slightly adjust TR1 to achieve a good chromatic tracking.
Frequency range : Apply a sinewave with frequency 32Hz to the audio input
Emphasis potentiometer to minimum resonance (fully counter-clockwise)
Turn the frequency knob fully counter-clockwise
Adjust TR3 (10K), in order to mute the 32Hz signal.
Emphasis : Adjust TR2 (1K) in order to reach auto-oscillation near 95% of the full range of the EMPHASIS pot.