The World’s FIRST Digital Reverb: EMT 250 Part 1 Demo with a Sequential Circuits Prophet-5

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"This is a 1976 EMT 250 digital reverb, one of not very many ever made. It came to the shop screaming white noise in my ear as soon as you turn it on, which ended up being a RAM issue. 12 bit (quasi 15 bit according to the manual as it converts the signal to floating point while it processes the signal, though I think they meant 16 bit as the RAM array is 8k x 16), 24 khz sample rate, probably around a 10 kHz roll off.

Part I discusses how to use it and you can hear some sound demos, part II will explore the circuitry of the unit a little more.

Shot and edited by Michael Shular"

Steelphon S900 // Mellotron M400

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"This is a demo of Tom’s Steelphon that got whooped by UPS - broken circuit boards, broken MDF case, no output. We took the case to be reproduced by Kent Meloy of Tunguska Guitars and in the meantime went to town on the electronics. There isn’t a schematic available anywhere, but after getting the rails back and the keyboard CV working, there was still no output. I isolated it to the filter board and realized the VCF is a Moog copy, component-for-component, so I used a Minimoog schematic to help troubleshoot the problem.

The Mellotron is mine and has undergone quite a bit of work. New pinch rollers, new motor control board, rebuilt the PSU, and fabbed a new key as one was missing."

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

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"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"

DeltaLab ACOUSTIKCOMPUTER DL-2 Professional Module Series

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Filing this one under synth effects. It's not a synth, but an effects rack with Reverb and Delay. Note the VCO used for Delay modulation.

See the DeltaLab label for additional posts featuring some of their other products.

Sequential Circuits Pro-One for John

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Roland Jupiter-8 for Tyler

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"Here is a demo of the Roland Jupiter-8 with a CR-78 and SRE-555 chorus echo. This JP8 had an interesting problem that many units with Encore MIDI have: an annoying click sound when moving any of the programmable sliders. It has since been solved and repaired and sounds lovely as ever!"

Arp Quadra for Randy

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"Foleytronics is a repair shop in the Cincinnati area (Dayton, KY) specializing in vintage FX, drum machines, synthesizers, tape machines and vintage pro audio. Every shipped item gets a video demonstration as assurance for the client, insurance for both of us and documentation of these cool old machines for the rest of the world."

IG: foleytronics_llc
www.foleytronics.com