[sdiy] current mirror for NPN expo?

[dan snazelle]

ok

so its not as easy as just picking the same cap value?  (i suppose the caps have a +/- tolerance )


On Sep 19, 2011, at 12:55 PM, Harry Bissell wrote:

> that is a different issue... I'd expect that the additional core must have its timing capacitor
> closely matched to the first, not at all easy to do...
> 
> H^) harry
> 
> 
> ----- Original Message -----
> From: dan snazelle <subjectivity at hotmail.com>
> To: David G Dixon <dixon at mail.ubc.ca>, synthdiy diy <synth-diy at dropmix.xs4all.nl>
> Sent: Mon, 19 Sep 2011 12:40:12 -0400 (EDT)
> Subject: Re: [sdiy] current mirror for NPN expo?
> 
> that is how i ended up trying it...however the pitch is not exactly the same on the second core...even though the part values are the same...i will keep working at it
> 
> thanks
> 
> 
> 
> 
> On Sep 19, 2011, at 12:15 PM, David G Dixon wrote:
> 
>>> can anyone point me towards info on how to use ONE NPN EXPO 
>>> to drive two vcos?
>> 
>> Can't you just mirror the current-sourcing one?  I.e., tie its emitter to
>> the other two, and connect its base to the other current-sourcing one?  You
>> should be able to replicate the current as many times as you want this way.
>> I did it with five transistors in a four-pole filter once; it worked a
>> treat.
>> 
>> 
> 
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> -- 
> Harry Bissell & Nora Abdullah 4eva
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