[sdiy] Super Bass Station Filter Failure

[Tom Wiltshire]

Did you find out from looking at the board whether the filter uses caps to ground or op-amp integrators? If it uses caps to ground, are the buffers op-amps or FETs?

Aside from these variations, these circuits are pretty standard and you could find a schematic that would be close. I've got some old Roland ones if you're interested. They *might* have tweaked values in some key parts, like the resonance path, but changing the actual layout without breaking it would be difficult.

The more variable part would be the control voltage handling - CV mixer, exponentiator, etc. This *might* be where the problem lies.

HTH,
Tom

On 2 Dec 2015, at 05:21, Matt Zapp <mattbzapp at gmail.com> wrote:

> 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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