[sdiy] 2164 SVF sound/noise?

[jays at aracnet.com]

Here's a couple of embedded questions.

Thanks
Jay S

David G. Dixon wrote:

> My additions to Tom's comments below:
> 
> > Others can tell you what they think, but here's my view after I have
> > played with these chips a fair bit.
> > 
> > > 1. Do they avoid the HISSY nature of OTA SVF filters? (the self noise of
> > an 13700 filter can be quite noticeable with no signal)
> > 
> > The SSM2164 is not as noisy as the LM13700. This isn't a carefully-
> > measured fact (for that we have datasheets - yeah, right!) but just my
> > perception. I've built a filter module with three of these filters in
> > parallel and even that isn't noisy.
> 
> I concur.
> 

I assume this is just a straight CA3080 type filter cell. What about the difference using the diodes in LM13700s or CA3280s and doing offset trimming. Is the noise still considerably more than the SSM2164.

> > > 2. do they SOUND different? or can you swear you are working with an OTA
> > SVF?
> > 
> > The SSM2164 sounds round and fruity. So yes, I'd say it stacks up well
> > against other OTAs. Way better than the CA3080, which is noisy as hell and
> > distorts like mad.
> 
> My 2164 4P LPF sounds every bit as good as my 13700 4P LPF, if not better.
> 
> > > 3. how is the resonance
> > 
> > Depends on the configuration. In the SVF, there are the much-discussed
> > problems of getting it even across the audio range. Aside from this, it
> > *sounds* good, even when it isn't even!
> > I know some other people have built 4-pole LPFs with this chip, so maybe
> > they can comment on those. I haven't tried that yet.
> 
> 2164 and 4P cascade filters were made for each other!
> 

I haven't done any real work on looking at the SSM yet and I'm wondering how topologies dealing with the virtual ground outputs of the SSM will effect sound. I've found 4P LP and 2P SV topologies out there but nothing like the cells used for the SSM, CEM and OTA for HP and AP. Yes you can chain a couple of SV filters together for 4P HP, 2P BP and 2P notch filters but the sound will probably be different than the old, 4 cell topologies. Any comments, ideas or suggestions here?