Don Voth has been servicing electronics for musicians, professional audio engineers and lighting technicians since 1989. Don started his own business in 2001: the Don Voth Electronics Company. Technology has evolved over the past 25 years, but Don Voth is still coming up with dynamic solutions; finding and fixing the most difficult and bizarre technical defects.
Just fixed this Mesa Boogie M-Pulse. The customer said that it was clipping to soon in the preamp. Honestly I though he was just setting it wrong but he was adamate that there was something wrong. So I agreed I would make a close examination of the preamp circuits. Turns out he was 100% correct. This pre-amp has a limiter circuit in it that will soft clip the the signal to no more than 1Vp-p. It is there to create very warm bass distortion at low output levels. The problem was this customer did not need that feature. So I defeated the limiter and then found the tube stage before it was clipping prematurely as well because the operating point of the tube was wrong. Modified the tube operating point and got a preamp with a huge increase in head room. Audio tested it and now you can turn the preamp to 3 oclock and it is still clean. Before 12 oclock was the limit.
Just fixed this Yamaha YC45D. It has no Touch Vibrato response. The touch vibrato is controlled by a shutter that sits between a lamp and a photo resistor. The lamp was fine. So no easy lamp replacement repair. I checked the keybed response. Thinking maybe that was worn and not pulling the shutter open fully. No such luck either. I adjust the sensitivity of the preamp and that got it to work but it still did not work well. So I modified the preamp to increase it's gain. I doubled the output of the touch vibrato going to the VCO. It was still not crazy Vibrato but as I recall they never were super responsive even when they were new. I used to play with them at the Yamaha Music Store when I was a kid and I recall that feature never did blow me away.
Yes. That is a MiniMoog and Yes, it is a working MiniMoog. That was not the case until the end of today. First, all the oscillators were not working. Fixed the -5V reference voltage and the Oscillators started to work but boy did they sound bad. Totally unstable. Turns out what was unstable was the Keyboard control voltages. So I refurbished all 129 key switch contacts, twice and then the keyboard voltages were fine. (See the switch contacts in the first picture.) Now I had to calibrate the oscillators but Oscillator ONE would not calibrate. So I fixed Oscillator one and then calibrated all 3 oscillators. Then I cut open the power indicator and replaced the Neon bulb inside so that the power indicator worked without loosing the factory look. And it all works now. GREAT!!