[sdiy] Discrete OTA

[Michael Bachman]

David

Interesting.. I still use the LM13700 in my filter designs, but have
been looking into the 2164...  You stated that  the 2164 "sounded
better".. could you try to define what you heard?   Is it the
exponential response that makes the difference?

I know the expo converter built in is nice for modular and CV control,
but that is not an issue for me, so I was wondering what else would
make me switch.. Sound quality would be the thing.

Thanks

Mike

On Fri, Apr 4, 2014 at 3:42 AM, David G Dixon <dixon at mail.ubc.ca> wrote:
>> There are plenty of well (and not so well) documented ways to
>> use the 13700 without the limitations you mention. The
>> criticism is better aimed at the circuit design rather than
>> the 13700 itself, so it is more a personal preference rather
>> than technical merit as to which to use. After all, the
>> SSM2164 input circuit is still the same diff. pair/ current
>> mirror topology as the 13700, but has internal feedback
>> remarkably similar (in concept, not implementation) to the
>> Mike Sims linearisation technique for the 13700.
>
> Yeah, maybe.  However, another nice thing about the 2164 is that it is
> exponential (nearly perfectly so), and therefore can replace not only the
> OTAs but also the exponential converter in filter circuits.  In fact, it's
> almost as if the 2164 was made for filter circuits.  All my filter designs
> sounded better when I replaced 13700 with 2164, and they involved much fewer
> parts.  I would never even consider using anything else for filters.  Having
> four VCAs in a 16-pin package rather than two OTAs is also much more
> convenient.
>
> In fact, if it weren't for the 2164, I would never have gone so far with
> synth design.  I owe that little chip a lot.  It really is the beating heart
> of every module I've ever designed.
>
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