Doepfer A-108 6/12/24/48 dB Lowpass Filter example

There are quite a few discussions about the quality of various modular filters / filter manufacturers, etc. which we are happy to see today. Here’s an example of the quite „beefy“ and full Doepfer A-108 6/12/24/48dB Lowpass (Transistor Ladder) Filter. Does it sound lika a Moog? I don’t care too much, since it sounds very fine in its own respect and fits well to all kinds of classical electronic sounds. For technical details of the 8 stage transistor ladder take a look at Doepfer’s homepage: 

The example uses three A-110 VCOs as input (all with sawtooth, one VCO is tuned down 1 octave), there is filter key tracking and filter ADSR modulation with varied intensity. You will hear the five different outputs of the filter as follows:

  1. 48 dB lowpass (0’00“ and 4’05“),
  2. 24 dB lowpass (1’00“ and 4’24“),
  3. 12 dB lowpass (1’42“ and 5’00“),
  4. 6 dB lowpass (2’20“ and 5’27“) and
  5. bandpass filter (3’00“ and 5’48“).

For each output, we start with no resonance (called emphasis here, since this is a kind of Moog clone) and end with full resonance. When using the bandpass, the center frequency is varied as well. After this, we repeat the same thing (slightly different filter center frequency) with input level cranked up so it can distort nicely. The VCOs are driven by an A-155 Sequencer.

Here we go:


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    Patch: three A-110s are mixed and then split into two signals: one is sent into an A-108 (24 dB lowpass output used) and then mixed with the other one in a polarizig mixer (here: A-138c). Original and filtered signal get opposite „polarizations“ in the mixer (i.e. one signal is inverted).

    Manual change of filter frequency – three times from low to high and back: without resonance, resonance at 50%, full resonance.

    With increasing resonance, the inversion of the filtered signal will be reduced drastically, so in the end, you will have a simple mix of original and lowpass filtered signal.


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