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Doepfer A-124 Wasp Filter


Module A-124 is a special 12dB multimode filter using the "strange" filter circuit of the "EDP Wasp" (an analog synthesizer with black/yellow case built end of the seventies, manufactured by the UK company "Electronic Dream Plant" with Chris Huggett und Adrian Wagner). This design "abuses" digital inverters as analog operational amplifiers leading to distortions and other "dirty" effects that generate the specific sound of this filter. The filter is equipped with a band pass output and a combined low/notch/high pass output. For this output a control knob defines the relation between low and high pass signal. If both signals appear at the same level (i.e. middle position of the Mix knob) one obtains a notch filter. Otherwise the low or high pass signal predominates. The module does not feature self oscillation in contrast to most of the other filters of the A-100 system.

Inputs: Audio In, CV In (2x)
Outputs: Bandpass Out, Low/Highpass Mix-Out
Controls: Audio and CV attenuator, Frequency, Resonance, LP/HP Mix

The function and operation of this module is very similar to the module SEM VCF A-106-5. But the sound of both filters is very different ! The only functional difference is the position of the sockets and controls, and the function of the controls CV2 (A-124: normal attenuator, A-106-5: polarizer).

Technical note:

The module is a copy of the filter used in the EDP Wasp synthesizer which "abuses" digital inverters (CD4069) as operational amplifiers. The disadvantage of this circuitry is that the inverters die now and then. The only solution would be to replace the inverters by standard operational amplifiers but then special character of the Wasp filter would be lost. It's impossible to predict if or when the CD4069 will die and of course we test each A-124 carefully before it leaves the factory. There are A-124 which work flawless since over 10 years, others become defective after weeks, months or years. Fortunately the CD4069 is a very inexpensive standard part (should be US$ 0.5 or less). The circuit is plugged into a socket and can be easily replaced by the customer if required.

Technical Specs

  • 8 hp
  • 6Current: +30mA (+12V) / -10mA (-12V)
  • Depth: 45 mm

      Brand: Doepfer

      SKU: DOEPFER-A124

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