SH-101 Low Pass filter thoughts

[acreil]

Originally Posted by seancostello

It would be interesting to compare the IR3109 filter w/diode clipping to a filter based around 4 13600 OTAS (+ external buffers) that used similar diode clipping, and see what kind of sonic differences result.

I think the 80017A clones use the 13600 or 13700 with op amp buffers. They're supposed to sound identical, at least according to the people who sell them. Of course there are no diodes in those.

I find the Korg NJM2069 also distorts a lot. In the Poly 800 and DW-8000 the power supply is only +/- 5V, so there's not a lot of headroom.

[zxcvbnm]

=seancostello;7545774]It would make for an interesting mod. For that matter, any cascaded OTA filter would probably take on an SH101 flavor with back-to-back diodes going to ground in the feedback loop.

Mind you, not all OTAs are made equal. I am not a big fan of the CEM3320, as it sounds kinda brittle to me. The LM13600/13700, and their equivalents, apparently use something similar to the CA3080, which has a nice tanh() overdrive response. It would be interesting to compare the IR3109 filter w/diode clipping to a filter based around 4 13600 OTAS (+ external buffers) that used similar diode clipping, and see what kind of sonic differences result.

It also depends on the type of buffer stages used.

Of course, everyone has different tastes. Some people love the precise filters in the Micromoog and Multimoog, while I prefer the coarser, more distorted Rogue filters. The Monotron has one of my favorite filters EVER,
and I suspect that the noise from the low voltage power supply adds to
the sound for me. Generally speaking, I'd rather have a thuggish
overdriven VCF than a filter with sharp resonance.

Hard driven S/K filters do NOT sound nice!............never!

[Karloff70]

Originally Posted by seancostello

The more feedback needed for a given Q factor, the higher the internal signal levels, and the more possibilities for tasty distortion. Not saying that this was the goal, but it seems like this was the result.

The SH101 uses the same IR3109 chip as the Juno-60, but has back-to-back diodes going to ground in the feedback loop, which will limit the self oscillation volume, and produces a raunchy sound as the resonance is turned up. The Juno-60 filters always sounded tame to me, in comparison to the SH101.

So if one was inclined to un-tame a Juno 6 or 60, one could go in armed with a handful of diodes and nothing else....? If so, that's interesting...or is there more. Stands to reason there might be. But if a bunch of diodes to ground in a feedback loop would render a Juno a gurning beast like a 101 I would take that as a challenge to pop one open......

[acreil]

Originally Posted by Karloff70

So if one was inclined to un-tame a Juno 6 or 60, one could go in armed with a handful of diodes and nothing else....? If so, that's interesting...or is there more. Stands to reason there might be. But if a bunch of diodes to ground in a feedback loop would render a Juno a gurning beast like a 101 I would take that as a challenge to pop one open......

It might be a better idea to try on a modular type thing first. If someone were to make a cascaded OTA VCF with maybe a tiny breadboard section where you could insert components, you could try swapping diodes like people sometimes do with distortion circuits: silicon, germanium, LEDs, two in series, various asymmetric configurations...

You could conceivably make a little auxiliary board that permits things to be switched between several variations. And in principle it would be more or less the same for any synth. But the effect might be overwhelming in a polysynth.

[audioconsult]

Originally Posted by acreil

I think the 80017A clones use the 13600 or 13700 with op amp buffers. They're supposed to sound identical, at least according to the people who sell them. Of course there are no diodes in those.

I find the Korg NJM2069 also distorts a lot. In the Poly 800 and DW-8000 the power supply is only +/- 5V, so there's not a lot of headroom.

maybee the diodes are outside the chip?

i just did 2 junos each with 2 broken voices with theese chips.. they had 13700 for filter and vca.. and i was highly sceptical.. but even for my ablton sound not as good as other daw´s ear they was just fine.. propper replacements