Thursday, January 05, 2012

Filters VI: A-122 24 dB Low Pass Filter VCF3

Module A-122 (VCF 3) is a voltage-controlled low-pass filter, which's circuitry uses a Curtis Electromusic chip (CEM3320), and sounds very similar to the classic Oberheim filter that was used in the OB8, OBX-a and Xpander synthesizers.
(and also in the Sequential Circuits Prophet 5 and Roland SH-101)

Because of its different circuitry and controls, the A-122 has a considerably smooth but thin sound, different like the A-120 'Moog-like' filter and other Doepfer filters.
Also the way the resonance behaves is quite different.

Luckily this module does have Voltage Controlled resonance that cannot only be controlled manually, but by voltages as well, right up to self-oscillation.
In this case, the filter behaves like a sine wave oscillator.
In this oscillation mode, you can simply use the FCV1 input to contol the pitch because it also works on the 1V/ octave rule, like regular VCOs.

I love the sound of it, you can use it to make fat and smooth basses up to the squelchier TB-303 style sounds.
A very nice filter, but not on top of my favorite filters list.
PatchPierre rating: 7/10

Check out the short (and not too in-depth) demo that i shot earlier today:
Video: Doepfer A-122 VCF3 Demo

" Short Doepfer A-122 Demo by NetPierre
Starts with a sequenced bassline, generated by my Doepfer MAQ16/3 and Doepfer VCO A-110 (saw wave)
Slow LFO sinewave A-147 into QCV input - ADSR into VC2 input
Drums provided by an Elektron Machinedrum "

As the special circuit CEM3320 used in this module is no longer available the module was discontinued.
Doepfer recommends the A-106-6 XP VCF, that is based on the filter circuit of the Oberheim Xpander, as a replacement module.