[sdiy] VCLFO core circuit..

[James Patchell]

     To answer your question...

     For non critical operation, you do not need to match those 
transistors.  I am not even sure if you can match a PNP and NPN, at 
least, I have never tried.  I use that particular expo circuit when I 
don't particularly care how it works.

      I would consider a different core for an LFO.

     Take a look in this schematic.  There is a page in there somewhere 
for a simple LFO.

http://www.noniandjim.com/Jim/SMBCheezy/100-1059.pdf




On 3/8/2012 5:44 AM, Jean-Pierre Desrochers wrote:
> 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.JPG
> Frequency/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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