[sdiy] Super Bass Station Filter Failure

[Matt Zapp]

Hey everyone,

I got my hands on a Super Bass Station rack for a song because the filter
does not sweep as low as it should.  I can't say specifically what the
cutoff is, I haven't measured it, but given a rough estimate I'd say it
gives up somewhere around 10kHz.  Needless to say, not terribly useful
right now, but maybe a fun repair project.

The good news is that I've traced the signal path all the way from the
front-panel knob to the various LM3080 chips that make up the filter
itself.  I haven't done an complete transcription of the circuit, a lot of
the passives are scattered to the winds on the board, and they packed the
entire synth into 40 square inches, but of what I could determine today
before getting a headache from squinting, the topology seems to follow a
fairly typical 4-pole, four-OTA pattern.  The filter is switchable between
12 and 24 db, but I haven't tracked down how they implemented that
parameter just yet.

The unfortunate news is that, after this deep exercise in trace-following,
I have a deeper understanding of how my broken unit works, but not
necessarily how a healthy unit *should* work.  To make up for what I lack
in patience and skill, I need either a service manual, a working Bass
Station filter for reference to see where in the circuit mine has
differences, or some pointers from you guys about how to go about narrowing
down the culprits.  I can certainly provide answers to questions, pictures,
or anything that would help anyone who wants to join me in the hunt.

In the meantime I've been knocking about the web for a schematic or service
manual with no luck, I even sent of an e-mail to technical support, but
rumour has it that Focusrite/Novation are notoriously stingy with their
assistance so I'm not expecting much from them.  If anyone knows where I
might be able to find one that would be stellar as well.

Thanks,
--Matt
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