Doepfer A-123-2 High Pass 6/12/18/24db

A-123-2 is a voltage controlled highpass filter with four filter outputs (6, 12, 18 and 24dB slope). It also features voltage control of the resonance.

These controls and in/outputs are available:

• Audio In with attenuator (Lev)
• Manual Frequency control (Frq)
• FCV1: Frequency control input (~ 1V/oct)
• FCV2: Frequency control input with polarizer
• QCV: Resonance control input with attenuator
• Manual Resonance control (Q)
• 6dB Output
• 12dB Output
• 18dB Output
• 24dB Output

Technical Notes:

The module is based on the special circuit CEM3320/AS3320. In highpass mode this circuit has a cleary higher CV feedthrough than other voltage controlled filters. With high audio levels or slow filter sweeps that's no problem. But with fast changing control voltage (e.g. ADSR with short times or a fast LFO) and low audio levels (i.e. the audio input level is clearly below the level where clipping occurs) a noticeable CV feedthrough may appear at the audio outputs.

With typical audio input levels (~10Vpp) from about position 5 of the level control clipping will occur. This is intended to generate distorted signals if desired. If applicable the level control has to be turned back so that no clipped audio signals appear at the outputs.