[sdiy] VCLFO core circuit..

[Harry Bissell]

I honestly don't know if a monolythic NPN/PNP pair has the inherent matching. You could say that the package
would be (roughly) isothermal, and that the PNPs would match and the NPNs would match.
I don't think that the NPN and PNP are necessarily matched to make a good expo converter.

One thing about the largely discrete ARP circuits, they are very fast. Very quick reset times, no
lag in the expo converters...

H^) harry

----- Original Message -----
From: Jean-Pierre Desrochers <jpdesroc at oricom.ca>
To: synth-diy at dropmix.xs4all.nl
Sent: Thu, 08 Mar 2012 09:30:41 -0500 (EST)
Subject: Re: [sdiy] VCLFO core circuit..


Thanks Harry
Ok,
Then if I'd use a PNP/NPN matched pair IC
available these days (which one..), would it be a good core
for a VCLFO ? 

BTW I'd also change the CD4011 for a good comparator.
I like this simple circuit approach.. but with good components.

JP


 On Thu 08/03/12 09:01 , Harry Bissell harrybissell at wowway.com sent:
> LOL. I once discussed this with Bob Pease (in specific about an ARP
> design)
> The transistors should be matched for equal base-emitter voltage drop at
> some reasonablecurrent (maybe in the middle of the expo operating range, certainly in some
> 10's to 100'sof uA.
> 
> See the trouble... you might try MANY different types of NPN and PNP
> without finding a really good match,and that would be different with each production run. That is why the
> manufacturers using this expo had suchhard times getting matched NPN/PNP pairs.
> 
> Much easier to match all NPN from the same batch, or use a monolythic dual.
> You are virtually assured of a matchthat way. Its more expensive (opamps) but those are dirt cheap now, not
> like in the ARP days.
> BTW BOB mentioned that Alan R. Pearlman was a simultaneous inventor of the
> "Darlinglton" trnasistor configuration, but hedidn't publish at the time so he was not recognised for having it first. It
> might have been called an ARPlington   :^)
> H^) harry
> 
> ----- Original Message -----
> From: Jean-Pierre Desrochers  ricom.ca>To: s
> ynth-diy at dropmix.xs4all.nlSent: Thu, 08 Mar 2012 08:44:58 -0500 (EST)
> Subject: [sdiy] VCLFO core circuit..
> 
> 
> I'm about to start building a set of  VCLFO modules
> for my synth so I browsed  a lot around
> to check for existing designs..
> I need it to track with 1v/oct input,
> (exponential response) but it would have lin inputs too.
> Most of the designs I saw use matched pairs of transistors
> for their expo converter part and sometimes
> hard to find parts.
> Looking around I thought it would be so easy to
> use the ARP Odyssey 2800 VCO core design..
> http://www.arcenson.com/public/Odyssey_2800_VCO_detail.JPGFrequency/temperature stability is not a big deal here but
> I'd use a TEMPCO anyway (R32).
> My question is:
> Are the two transistors Q4, Q5 matched or only
> stuck together for thermal transfer and stability ?
> and if they are matched how are they ?
> Thanks
> J-Pierre
> 
> 
> 
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> ynth-diy at dropmix.xs4all.nlhttp://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> -- 
> Harry Bissell & Nora Abdullah 4eva
> 
> 
> 
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