[sdiy] Intro, and saving the 901?

[Tony Allgood]

Hi Richard,

Welcome to the the list.

> Is the Minimoog osc design worth trying instead? How is that for temp
stability?

There are three versions of the VCO. The second version is supposed to
the best sounding, but I have yet to hear one.

The first VCO design is all discrete, but rather different to the 901.
Its more like a ARP in the core but with a discrete op-amp summer and
expo. I tried to clone this issue, but I could not get it to work
without having major problems with the scaling. I spent some time on it,
and enountered several problems with scaling accuracy. The problem lay
entirely with the expo... but after I had trashed two SSM2220 matched
pair PNPs I was off the case. This was getting too expensive.

The third version uses a uA726 heated NPN pair in the expo, and needs
some rework to be useful. I use the core of this VCO in my own VCO
design, and I am very happy with its stability and sound. I use a
standard temp co resistor in the expo with superb results.

If you are in the UK you may be interested in the UK synth-DIY do. Paul
Maddox is holding this event in December in Hereford. I hope Keith
Winstanley will be going too, so we can see the Moog 904 VCF module
clone he did.

Regards,

Tony Allgood                       Penrith, Cumbria, England

Oakley Sound Systems                     www.oakleysound.com
Modular projects            www.oakleysound.com/projects.htm