Sent Fri, Mar 3rd 1995, 18:11
Hi! Time to send a message to AH again. Well, now. Some of You (mostly Europeans :->) suggested a meeting at the Musikmesse in Frankfurt this year. I will be there, either Thirsday, Saturday or Sunday, and I would be happy to meet some of You on this occasion. If there still is interest, I'd like to know which day You would be better, and I'd suggest meeting at Touched By Sound's exposition, 'cause the guys know me and You could ask for me there. What do You think? Second thing, just to share with You: Since Saturday, I am the proud owner of an *absolutely* mint condition Prophet 5 (Rev. 3.0). Man, I didn't know that things like that still existed! Not the slightest scar on the wood or on the panel, not the slightest particle of dust (It was sold to me with a dust-cover ...); I believe this instrument has never seen a stage even from afar. It all looks as if it was manufactured last week, and not years ago. There was, however, a tuning problem with VCO B of voice 3. It wasn't due to a bad Curtis (And I believe that was the thing the seller had tested before parting with it ...), but there was a leakage in the demultiplexer/sample&hold circuit. A degradation of a TL082, about 20MOhms. After 3 hours of searching I found that there was a 100mV discharge in the capacitor every scanning period that made the VCO go flat .. well, a new TL082 ( less than $ 1,- ) fixed the problem! During my search for the error source, I found something rather interesting (to me, at least): I wanted to check if dirt on the PCB was responsible for the leakage, and I sprayed different cleaner fluids onto the multiplexer region. This didn't cure the problem, but caused other VCO's to go flat as well (until the fluid was vaporized). All in all I can say that this MUX part is *very* sensitive to dirt and leakage, and anyone who has exchanged VCO chips in vain should also look in that direction when tuning problems occur. Tonight, I will replace the noisy, designed-for-60-Hz transformer by a toroid one. Finally, a dream has come true for me. JH.