[sdiy] Problems with linearized SSI2164 ?

Pete Hartman pete.hartman at gmail.com
Thu Feb 14 23:25:20 CET 2019


100k x 22p vs 100p x 30k.  An order of magnitude from 22p x 30k either
way.....

On Thu, Feb 14, 2019 at 3:13 PM David G Dixon <dixon at mail.ubc.ca> wrote:

> Increasing the resistors from 30k to 100k also fixed the problem, with the
> same 22pF cap in place.
>
> ------------------------------
> *From:* Synth-diy [mailto:synth-diy-bounces at synth-diy.org] *On Behalf Of *Mattias
> Rickardsson
> *Sent:* Thursday, February 14, 2019 12:53 PM
> *To:* Dave
> *Cc:* Synth DIY
> *Subject:* Re: [sdiy] Problems with linearized SSI2164 ?
>
> Den tors 14 feb. 2019 20:49 skrev Dave <dlmanley at sonic.net>:
>
>>
>> This is a GBW/ phase margin issue?  Indicating the SSI part has greater
>> GBW so is less tolerant to a reduced cap value?
>>
>
> Maybe? Or is it the op-amp that matters?
>
> Anyway, the circuit had values outside the recommendation. We shouldn't
> expect makers of drop-in replacements to specify how their product behaves
> versus the original in an unrecommended application.
>
> Btw, we're actually touching one of the hidden advantages of the SSI part:
> With the old 2164s in the ordinary VCA configuration with 30k resistors,
> one might be tempted to use quite small feedback caps in order to not
> introduce noticable HF roll-off under 20 kHz. With the doubled current
> capacity of the SSI2164 the resistor values can be halved (for reaching the
> lower noise specification), meaning that the cap value can be doubled for
> the same roll-off. So in practice, perhaps even better tolerance for the
> needed cap values. :-)
>
> /mr
>
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