[sdiy] VCLFO core circuit..

[rob at emulatorarchive.com]

Hi,
I have found the THAT 340 and 300 provide a few good basis for 
replicating the ARP VCO with its NPN/PNP expo pair and CA3046. Frequency 
stability has improved from a pair of 2N3904/06's which are replaced 
with the 340 - presumably because they are on the same die, and I have 
yet to pot the sub module which I have find improves stability further. 
This revised design is the basis of the AM8027 VCO which can be found 
here, http://www.amsynths.co.uk/Products/AM8027/am8027.html. I will do 
some proper tests of frequency stability and log conformance and post 
the data online. If anyone wishes to use the VCO core its available as a 
49 x 49mm PCB and it fits into a 50mm potting box.

All the best - Rob

On 08/03/2012 15:04, Harry Bissell wrote:
> 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
>>
>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> S
>> ynth-diy at dropmix.xs4all.nlhttp://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>> -- 
>> Harry Bissell&  Nora Abdullah 4eva
>>
>>
>>
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