AW: [sdiy] Roland System 100 - Circuit details.

[Czech Martin]

What about measuring the dc input bias variation of the differential amp
instead ;-> I mean , no signal , just the control feedthrough.
btw.: are these transistors matched for transconductance???
I bet: no.

I read once about such diode circuits:
match the diode pairs, the dc forward characteristic should at least
match in 2 points, i.e. the forward I/V curves should
be matching.

Matching transistors is something different, because you can
ride the collector low or high, as long as you don't
saturate this is not so important.

Your ladder is not matched in this sense.
At least I think so.

m.c.

> -----Ursprüngliche Nachricht-----
> Von: Tony Allgood [mailto:oakley at techrepairs.freeserve.co.uk]
> Gesendet: Freitag, 7. September 2001 13:56
> An: Synth DIY
> Betreff: Re: [sdiy] Roland System 100 - Circuit details.
> 
> 
> >Ok, the transistors in the moog ladder are tied to the 
> voltage divider
> chain via base,  that way the internal nodes (caps) will not 
> float very
> much up and down during sweeps. Diodes simply don't have a 
> base and will
> therefore fly up and down.
> 
> Yes, these were my thoughts... so I replaced the unmatched 
> pairs in the
> SH-2000's filter with 2SC3381 with matched ones and got no difference
> whatsoever. There is another thing going on here. If I get some time,
> I'm going to simulate some of these circuits.
> 
> Regards,
> 
> Tony Allgood, Penrith, Cumbria, England
> 
> Oakley Modular Synth and TB3030:
> www.oakleysound.com/projects.htm
> My music: www.mp3.com/taklamakan
> 
> 
> 
>