New Stuff

[mbartkow at ET.PUT.Poznan.PL]

Hi JH and list. Thanks for the explanation, but let me point something and
ask further:

> Let me first answer with a question in return: Why does the widely used 
> OTA / opamp buffer VCA circuit use as many as 6 gain stages ??
[...]

IMHO the main reason is that they are required to have an extremely high
gain in an open loop. In a VCA there is no global feedback which would 
potentially reduce the gain, moreover we usually operate on somewhat stan-
dardized line levels (at least in modulars it should be so), therefore we
do hardly need any gain, rather a controllable attenuation. Am I right to
suspect more stages mean higher dynamic range ?

> To answer your question: In the Minimoog, one stage was used for VCA
> envelope,
> one stage was used for Pedal Volume control, and the last stage is a class
> A buffer amplifier / line driver.

Well, sasn't it easier to control the first stage by a sum of ADSR CV and 
the external input? 

Finally, what do you think about differential pair with fully balaned dynamic
load by a current mirror ? Like the one proposed by Roman at
http://www.multimania.com/romcio/m_modvca.gif
I must admit I love the simplicity of his ciruit.

regards,

MB


--

Maciej Bartkowiak, PhD
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