[sdiy] VCLFO core circuit..

[Harry Bissell]

from THAT semiconductor website

"The THAT 300, 320 and 340 are large geometry, 4-transistor, monolithic NPN and/or PNP arrays. They exhibit both high speed and low noise, with excellent parameter matching between transistors of the same gender."

I'm taking "of the same gender" to mean the NPN and PNP are not inherently matched.

That said I've done the npn-pnp expo with generic transistors (3904/3906)and had acceptable results for things like VCF where expo
conformity isn't too critical (at least to me)...

If I wanted accuracy I'd either feel the (extreme) pain to match the NPN-PNP, or use another topology...

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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