Doepfer A-102 Diode Low Pass Filter

The A-102 is a 24 dB lowpass which uses diodes (and not transistors), which leads to quite unusual resonance behaviour (resonance is dependant on filter frequency). The filter can easily be overdriven, which adds some interesting harmonics.

In this sound example, I use three A-110 VCOs (sawtooth, one VCO tuned down 1 octave), mixed and put through the A-102 and then into an A-132-3 VCA. Both VCA and filter are controlled by an A-140 ADSR, the sequence is made with an A-155/A-154 Sequencer.

Technical details on the A-102 can be found on Doepfer’s Homepage:

  • We start with comparably low input level, no resonance and cutoff frequency at minimum. Then I manually increase cutoff frequecy up to maximum and back to zero.
  • Starting around 0:35 same procedure, but with medium resonance (value ca. 3)
  • From 1:10 on: full resonance.
  • Then back to zero resonance, but from 1:50 on maximum input level.
  • Starting at 2:25 we hear medium resonance again (full input level).
  • Finally, around 3:05 we have max resonance and max input level.

Here we go:

Have Fun,