[sdiy] Problems with linearized SSI2164 ?

David G Dixon dixon at mail.ubc.ca
Thu Feb 14 22:10:30 CET 2019


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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