RC Filtering for SSM2164 CVs fed from DACs

Posted by & filed under Filters, Synth DIY, VCAs + Amplifiers.

I typically use the 12-bit MCP4822 DAC to produce a CV for the SSM2164 (or CoolAudio V2164, it’s the same thing) . This is a good, cheap combination. However, the 4822 produces an output of 0-4.095V, whereas the 2164 needs 0-3.3V. It is possible to use a simple voltage divider to reduce the voltage to the correct level, and it is also possible to add a capacitor to give an RC 6dB/Oct rolloff whilst we’re doing it. However, it’s not… Read more »

CEM3320 Filter designs

Posted by & filed under Elka, Filters, OB-Xa, Oberheim, Pro-One, Sequential, Synth DIY, Synthex.

Like my SSM2044 page, this page is a look at how various synths implemented the CEM3320 filter, with the datasheet design as a reference standard. Whereas the SSM2044 is a dedicated lowpass filter, the CEM3320 is just a set of filter building blocks. In this respect, it is more like the earlier SSM2040. The CEM equivalent of the SSM2044 is probably the CEM3328, which is basically the same as the 3320, but wired up as a dedicated lowpass filter, thereby… Read more »

SSM2044 LP Filter designs

Posted by & filed under Filters, Korg, MonoPoly, Opera, Polysix, PPG, Siel, Synth DIY, Trident, Wave.

This page is a look at how various synths implemented the SSM2044 filter, with the datasheet design as a reference standard. I’ve redrawn all the schematics to make comparisons very easy. First, the datasheet design.   The datasheet suggests using the two differential inputs (+audio and -audio) as individual oscillator inputs for a two-oscillator synth (or synth voice). It also suggests that these two inputs should be provided with slightly different resistor values (68K Vs 100K) so that the oscillators… Read more »