Ultimate VCO 1 voltages

Emusicman · Joined: Jun 17, 2018 Posts: 6 Location: Canada

Good morning everyone, been working on Ray Wilson's Sound Lab Ultimate, been going through the initial checks he post on his website. So far everything was checking out pretty good. Went to do the calibration of the VCO's starting at number 1 and the coarse and fine pots seem to be reacting like they should, then I noticed that the high frequency Trimpots on 2 and 3 I soldered in backwards, took the synth out of the case to repair the pots, I did number 2 and then not thinking and rushing instead of 3 I desoldered 1, put that back correctly and continued to 3. They are all done and correct. Next morning went to do the calibration on 1 and now it is not reacting like it should. Instead of -9.5 to +2 volts on the pot I am getting -12 to -3 volts on the pot. When I try to set the initial frequency of 100 Htz it takes way over 50% of pot rotation for the VCO to even start registering anything, another error I may of made was my Frequency Probe was connected to Pin 1 of U2 instead or U4, could the probe connected to U2 caused any damage to the IC. My troubleshooting skills are at the learning stage of my aptitude as prior to working on synth projects I was heavily into Vacuum Tube guitar amps, prior to the Ultimate I have worked on other Synth projects that seem to go very well so that is why I decided on this new project.

Thanks in advance for any tips
Steve

khakifridge · Joined: Jul 15, 2014 Posts: 27 Location: UK

You won't want to hear this, but there's not really a "backwards" with trimpots (since there's no front-panel knob, where clockwise and counter-clockwise might have some meaning). So it's something else... Start by checking the values of R1, R2, R4 and R5 are correct (this is basically the start of Ray's own troubleshooting notes on the VCO calibration process).

And unless your probe shorted out two adjacent pins, and one of those was power, then you're unlikely to have damaged anything. I did exactly this on a sub-mini tube once and it lit up like a bulb! Briefly... Rolling Eyes

Emusicman · Joined: Jun 17, 2018 Posts: 6 Location: Canada

Sorry about the late response to everyone but after checking parts being correct and my panel wiring being correct, they worked out fine. In Rays troubleshooting guide I went to see if the actual components were working like they should. I noticed the SSM2210 at VCO 1 the heatsink compound dripped all over the legs of the IC. After studying more of the schematic I replaced the 2210 and also I had to replace the TL072CP's. The TL072s I bought either from a Hamfest Flea Market of a vendor in China the might have been a bunch of seconds. On VCO 2 calibrating was good, on 3 the scale trimmer and the high frequency compensator were not reacting like they figure they should. Replaced the TL072s in that circuit and low and behold calibration went off without a hitch. With my projects I have on the go I didn't have enough of the 072s from the unknown vendor and in one of my Mouser orders I bought 20 of them so I was able to swap out the chips.
Thank you and stay safe

Steve