Doepfer A-124 Wasp Filter Schematic

• Feb 19, 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.
• Just like the A-199, this module also lacks any kind of protection on the power input.