Doepfer A-124 Wasp Filter Schematic

• Feb 19, 2025
• edited: Mar 26, 2025

I have been thinking about the EDP Wasp filter for a while — the way it abuses CMOS inverters as opamps is very interesting. There are a bunch of clones of the filter around, the most notable one probably being the A-124 by Doepfer. I’ve been curious about what changes Doepfer has made to the circuit for a while, but there is no schematic available. For a while I was planning to buy an A-124 just to reverse-engineer it.

Recently Behringer announced their own Eurorack Wasp filter clone and the controls being identical to the A-124 sparked some discussion about it possibly being a copy of Doepfer’s module. During this discussion, someone in the Modular in a Week community mentioned they have an A-124 and I asked if they could send me photos of the PCB so I could trace out the schematic. They agreed and sent me the photos, so here’s the schematic.

• A-124_WASP_VCF-schematic.pdf (0.2 MiB)
• repository/A-124_WASP_VCF.kicad_sch (0.2 MiB)

Notes

• This schematic is based on the version V4 of the module.
• I’m pretty confident that this is right, but there could be some mistakes. If you notice any, please let me know.
• Most component references are missing, because I couldn’t see them in the photos. If you have an A-124 and want to help by peeking at the references under the components, get in touch.
  • (Update 26.3.2025) Thanks to Misha Sannikov for adding the references for ICs, potentiometers and jack sockets. References for resistors are still missing because they need to be desoldered to see the references under them.
• Just like the A-199, this module also lacks any kind of protection on the power input.