AM8104

AM8104 JP04 VCF

The AM8104 is a clone of the Low Pass and High Pass Filters from the legendary Roland Jupiter 4 analog polyphonic synthesizer that was launched in the autumn of 1978.

Early versions of the Jupiter 4 used a Rohm OTA chip the BA662. It is this version that is replicated in the AM8104. Later versions used the IR3109 filter chip, which is replicated in the AM8109 JP8 filter module.
Roland first started using OTA based filters in the 703E and 703F modules in 1976, as part of the giant 700 Modular System. This design was reused in many follow on products, including the System 100M and SH-2. Each design revision has small component changes that make for a subtle change in the sound.

The AM8104 includes the 24dB low pass filter as well as the single pole high pass filter, providing the characteristic warmth and powerful resonance of the Jupiter 4. The filters use BA6110 OTA chips from Rohm, the successor to the BA662.

High quality components are used throughout the filter including polypropylene capacitors in the filters.
The AM8104 includes a keyboard follow feature which enables the keyboard CV on the Doepfer bus to effect low pass filter frequency cutoff. Some Eurorack keyboards like the Waldorf KB37 include this signal in the design, alternatively a simple keyboard CV and gate breakout module can be used.

https://www.amsynthstore.co.uk/AM8104_JP04_VCF/p1461448_18640793.aspx