Time for my semi-regular posting on stealing voice-card parts.
If you need a VCO or VCF, etc, it's pretty easy to steal parts from one or both of the 8th voice cards and then disable that card. You'll end up with a 7-voice synth, which is probably not noticible for most folks - at least until you manage to get the missing parts.
One the KAS board there are two changes:
* There's a resistor from each gate output of the KAS chip (KO1-KO8) to -6.5v. Change the one on KO8/pin39 to instead have the resistor connect to +8.5v. That tells the KAS chip that it can only play 7 notes.
* Then disconnect one end of D8. D1 - D8 "OR" the 8 voice gates into the monophonic gate, TR9. This is used to trigger the Ring Mod envelope. If you don't do this, that envelope will always think you're holding a key down.
* Speaking of which, the TR8 to the two voice cards for voice 8 will now always be gated on. Therefore, you need to disconnect the audio output of these two boards. This is the O (pin 33) pad, which is the third pad from the bottom edge of the board when the card rack is raised. Is had white wires coming off of it.
You need to heat up the pad and remove both white wires and make sure they are still connected to each other and then wrap them in electrical tape or heat-shrink tubing. The outputs of the 8 cards are all just shorted together by the daisy-chain of white wires which just end up at the Mix control on the front panel. One of the white wires is going to the control and the other is coming from the voice 7 card (and therefore voice 1-6 also) so if you don't make sure they're still connected, you'll have no sound.
Enjoy!
David
On Oct 17, 2013, musicalfix@... wrote:
Thanks, it's great that you have these and other such ICs. It seems these VCOs can be in a state where they are working but not able to meet the specs. I had one which couldn't make the top octave frequencies are some whose scaling has drifted. I will see how my customer feels about it, and let you know if I need anymore.
---In yamahacs80@yahoogroups.com, <synthparts@...> wrote:
So the problem is with the IG00153 VCO chips you think? I still have a few in stock if you want any...
---In yamahacs80@yahoogroups.com, <yamahacs80@yahoogroups.com> wrote:
Hi. Thanks for your reply. On your advice I did replace the caps on the S/H board which got rid of some unwanted crackling. Then went back and re-calibrated the power supply, S/H and KAS boards.
Which I had already done, but the tolerances are small and some were out. Also the transposition gate zeroing on each voice shifted a bit (0mv between cp6 and EK). The tuning was then better, but still three or four voices were 20 or 30 cents flat on the lower octaves on the 8 and 16 feet ranges. Eventually I tried swapping the VCO chips around and found the fault moved with the VCOs. So I think I cannot improve it any more.
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Sent from my Android phone with K-@ Mail. Please excuse my brevity.
