[sdiy] Re: 5pole diode filter

[Tony Allgood]

Hi Juergen and all,

>I thought I unsoldered a string of equal resistors when I used a
SH-2000 keyboard for my JH-720, to replace them with 3-values resistor
ladder for Korg linear VCOs.

When I saw your modifications to the SH2000's keyboard I wondered why
you did that. The SH2000 has hand selected resistors in one chain to get
the desired expo response direct from the keyboard. As far as I am aware
the design of this never changed throughout the various versions of the
SH2000. I think the reason is that the 2000 was designed to go with home
organs. Therefore it needed to be totally rock stable in tuning. I
tested mine when I got it... the tuning trimmers had never been touched,
they still had the loctite in place. And it was still tracking to +/- 1
cent across the whole keyboard. After 25 years, now thats impressive!
The VCO itself only runs across 3 octaves, any octave shifts are done
with dividers. It will be interesting to see if it can actually cope
with more than that directly through the CV.

The SH1000 and SH3(a) are ordinary expo VCOs I think. Obviously the
regular music market can cope with a bit of re-tuning now and then :-)

BTW: The VCF in the 2000 is expo at 2V/octave but is driven from a log
amp. The log amp sits on the VCO board, and the expo on the VCF board.
EGs and LFOs are added in between to get the right feel.

Regards,

Tony Allgood  Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan