[sdiy] current mirror for NPN expo?

[Harry Bissell]

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