[sdiy] current mirror for NPN expo?

[David G Dixon]

yeah, this "driving two VCOs from one expo" idea is a non-starter, I'd say. 

> -----Original Message-----
> From: Harry Bissell [mailto:harrybissell at wowway.com] 
> Sent: Monday, September 19, 2011 9:56 AM
> To: dan snazelle
> Cc: David G Dixon; synthdiy diy
> Subject: Re: [sdiy] current mirror for NPN expo?
> 
> 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