SSI2144 and SSM2044 Comparison
Overview In 2017 Sound Semiconductor launched the SSI2144 voltage controlled low pass filter, a re-engineered SSM2044. At AMSynths we have used both chips in our modules; the SSM chip in the AM8044 (2014) and the SSI chip in the AM8144 (2018).
We also make adapter PCB's that convert the different pin out of the SSI2144 to the SSM2044 pin out, this enables them to be a drop in replacement for synthesizers that use the SSM chip.
The SSI chip has a set of minor but worthwhile improvements and specifically the resonance control has on-chip control, and the Q control current for oscillation has been reduced from 425uA to 400uA. The Q control suggested external circuit is also slightly different to the SSM version.
So lets hear and see a comparison between the two chips with the same input signal at 50Hz from an Emu Systems Modular VCO, as I dial up the resonance from zero to maximum.
Original SSM2044 Here is the SSM chip manufactured in March 1987 notice the longer duration before oscillation comes in.
Re-imagined SSI2144 And now the SSI chip from 30 years later, notice the oscillation comes in quicker. In our modules we use the recommended Q external circuits for each chip, and we trim the onset of oscillation when setting up the modules for customer shipment. So our modules will sound similar.
In polyphonic analog synthesizer with a mix of SSI and SSM chips the resonance trimmers will need to be adjusted when a SSM is replaced with an SSI, or better still replace all the 2044's.