MATRIXSYNTH: EXTREMELY RARE PPG 1002 for Tom + first ever shop tour!!!

Saturday, December 09, 2023

EXTREMELY RARE PPG 1002 for Tom + first ever shop tour!!!

video upload by foleytronics fx repair

"Here is a demo of the EXTREMELY RARE PPG 1002 for Tom. Plus a bonus first ever tour of the Foleytronics shop!!

For those that want to attempt to tune this synth, here is what worked for me:

The trimmer by the regulators is the CV offset; trim for 0v for the lowest key. This interacts with the CV v/oct, which is right above where the two shielded cables connect from the 20-pin keyboard connector. Trim this for 1v/oct, which can be measured at the switched oscillator CV input jack on the back of the instrument. Once these are set, you can move on.

The oscillators are tricky. They each have an initial frequency trim pot and a volt/octave trim pot. However, the initial frequency trimmer cannot be set willy nilly to A440 because their initial tuning frequency greatly affects the octave selection switches on the top panel. What I found to be most effective is to set the MASTER TUNE front panel pot to 0, the OCTAVE SLIDER to the left of the keyboard to the middle and then begin tuning. Note, every trim pot for each oscillator will affect the others for that oscillator so this is an exercise in extreme patience.

First, turn off keyboard control for OSC B and roughly center its front panel tuning pot; set its octave to +3 and put a folded piece of paper on middle C. You are now going to tune the octave selector for OSC A; this part is confusing as there is a trimmer to adjust the octave selection offset for BOTH oscillators, but only OSC B has an adjustment to “match” its octave selection with that of A. Thus, you have to use that trimmer to get OSC A perfect and then match B to A - the method that worked for me was to switch between octaves for OSC A and adjust the octave offset trimmer along with the initial frequency trim pot for A to get a perfect octave selection for OSC A over the OSC B drone.

After the OSC A octave adjustment, it’s time to adjust B’s octave adjustment. Set A to +3, and switch OSC B to +1; adjust for zero beating at the trimmer in the upper left corner of the board right at the edge of the PCB. Then, switch OSC B back to +3 and adjust its initial frequency for zero beating; repeat this until the octave selection is perfect for B.

Now, it’s time to adjust for V/octave for each oscillator. Sadly, this adjustment affects the octave center calibration we just did, so you’ll have to keep backtracking until it’s good. Adjust the V/octave trim pot for OSC A, which is directly to the left of the CV v/octave we did in the first step. You’ll now have to mess with the init. frequency for A along with the V/oct to get the oscillator to track correctly on the keyboard, but like I said earlier, you have now probably slightly messed up the octave selection so you will have to go back and do that again. Then, adjust the tuning of OSC A again and repeat this process until OSC A tracks perfectly and has good octave selection. I couldn’t really get the +4 octave to be perfect, but hey, it’s a prototype and is probably 50+ years old.

Now for OSC B; it’s very similar to A. Use the V/octave adjustment trimmer which is the lower left trim pot on the PCB along with the initial frequency trim pot to get B to track along the keyboard. Again, you’ll have to go back and adjust the octave selection, but that’s not as bad for B because its octave adjustment doesn’t mess up OSC A’s octave selection. At this point, you should be able to get OSC A and OSC B to track the keyboard and the octave selections should be there"

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