AM 4023 Module - ARP 12dB Low Pass Filter



Overview This was the first module I designed back in the Autumn of 2002.
It was a prototype for later designs and many lessons were learned... (PCB holes too small, no mounting system). The production PCB produces an excellent sound, just listen to the MP3 download.

Original Circuit  The ARP 4023 filter was designed in 1972 as a 12dB (2 pole) voltage controlled Low Pass Filter, and it was used in the original "white faced" Odyssey. It is a 2-pole OTA design based around transistors, the CA3080 (or OTA) and the LM301 Op Amp. The filter will self-oscillate at higher Q settings and it is temperture compensated with a 1K87 tempco resistor.

AM Circuit I have kept the CA3080 OTA's and used matched and thermally coupled 2N3904/2N3906 transistors. I have upgraded the Op Amps with high quality Burr Brown OP177's for CV summing and OPA134's for audiol paths. All capacitors are high quality WIMA versions or 1% polystyrene.

Specifications  The AM4023 filter has been analysed for its frequency response, dymanic range and noise. The filter has been compared with the AM4075 which has a lower frequency range.

The AM4023 filter has a frequency response of 120Hz - 11kHz at -3dB.

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Module PCB for sale!

Sound Clip

The Original