My Moog 55 has held up amazingly well over the years. It's now 40+ years old, and with the typical minor maintenance here and there, its still sounding and working great. I've performed various modifications to it over the years as my needs and familiarity with its strengths and limitations have evolved.
Modifications?!!??!?
What modifications????
Why, I'm glad you asked!
The idea of performing modifications on vintage, even iconic equipment can often be a prickly subject for many synth enthusiasts, and as somebody who's seen his share of mods, both good and bad, I'd like to discuss my personal views on the subject. I've customized quite a bit of the gear I've owned over the years, and bought my fair share of used equipment on the cheap that was brutalized with poorly executed modifications that would seem to have limited (or occasionally, unknown) usefulness. I look at my collection of equipment as tools for music making, and if a modification makes that tool noticeably more useful to me and I can do it cleanly without compromising the unit's integrity, then I'll do it. I try to make any mods look as professional as possible, keeping with the particular look of the gear involved if possible.
When I first got interested in synths back in the early 70's, there was absolutely no way I could afford to buy one. I scrimped and saved and eventually bought and built a modular kit from PAIA, but the sound and performance of the finished unit left a lot to be desired, even for a novice like me.
Back then, I was in the Air Force, working by myself on the night shift, with pretty much nothing to do from midnight to 7am (my job was basically to call the command desk if something truly horrific happened which thankfully, never did). Having recently discovered the wonderful how-to newsletter called Electronotes...
...I decided that I could probably build my own synth and do a better job of it (man, was I optimistic!).
I had no money but lots of free time, and after gathering service manuals and schematics for the synths I was interested in (much, much harder to do back in those pre-internet days!)...
...and purchasing the necessary and hard to find parts from the ads in the back of various electronics magazines, I started teaching myself how to make circuit boards and build and test synth modules, one section at a time. It was slow going, but over the period of about a year, and with LOTS of trial and error, I had a reasonably working synth that was a cross between a Minimoog, Sonic Six, and an Oberheim (just funkier looking, and thanks to the rat's nest of wires inside, less reliable). I built everything into the wooden case for the old PAIA, made a new aluminum front panel in the Air Force machine shop, and my then-girlfriend painted a lovely sky scene on it with her acrylics. I added some retro-looking knobs and some futuristic computer font labeling with Letraset rub-off lettering...
...and I was in business!
As I slowly combined all this stuff together, I had the time to think about and make all sorts of decisions about how I wanted it to work, and it was these sorts of custom modifications to the basic accepted scheme of things that guided and informed my work with later manufactured synths (once I could actually afford to buy a few). It seemed that there was always various things I wanted them to do that the designers hadn't thought of, so I would attempt to figure out how to add these features myself if I felt it was really necessary.
This brings us back to the history of the various modifications that have been performed to the Moog 55, and some insight into the reasons why they were done. Once I got it home from the college, and before I could get it on stage, there were a few basic problems that needed to be sorted out...not really surprising after the years of student (and probably gong-banger) abuse. I called and ordered the service manual for the Modular system from Moog (what we had to do before the internet), and spent some time going over the various schematics.
The envelope generators all seemed to have a low and unstable output. Looking at the circuit boards, I found that all of them had burned 100 ohm resistors in the output stage, probably the result of them being plugged into other outputs that were trying to source voltage as well (maybe stuff like the keyboard, sequencer or oscillator outputs, but who knows?). Replacing these damaged resistors had all of them working normally again.
The pitch of the system would go squirrelly at times as well, and I was able to track this to the -6 volt supply, more specifically to an intermittent voltage adjust pot in the power supply. After disassembly, cleaning, and readjustment of this dodgy pot, and a complete calibration of all the various modules in the system,everything was back to normal, it sounded INCREDIBLE, and it now seemed ready for live performance. After the first few gigs with the Moog 55, my experiences definitely gave me a couple of ideas about what would make it more useful and reliable in a live performance setting.
At the first gig, I had a fairly complex lead patch set up that mysteriously quit working properly shortly into the first solo. An inspection at the first break between sets revealed that I had accidentally knocked one of the switch trigger cables loose, and since I couldn't see if the various envelope generators were working or not through the maze of patch cords, I couldn't effectively troubleshoot the rig in the heat of a solo.
I was also using the big 921 oscillator as an LFO (a waste of its mighty resources, as we'll talk about later) and I had no way to silently set various rates for different purposes with any degree of accuracy while in the middle of a performance.
Back in my workshop a few days later, I added an LED to the Envelope Generator trigger input to show if and when it was being triggered, and after thinking about it for a while, I also set up an output LED that followed the envelope output voltage swing, getting brighter and dimmer as the envelope cycled through its paces. There was lots of unused blank space on the module's circuit board, and after prototyping and perfecting the circuits involved, I just drilled the necessary holes for the components in a blank area and built the mods right onto the board.
Press-in collars for the LEDs made them look at home on the front panel, and gave the mods a nice professional touch.
I tried this on one envelope module and really liked the added functionality, so I modded the remaining ones, which added a bit of audience visual appeal to the system as well.
I added a pair of dual color Red/Green LEDs to the differential outputs of the 921 oscillator so I could tell where the waves were during a cycle, and see the current LFO rate more easily.
Other mods involved installing normalled jacks in a few key places to reduce the number of patch cables necessary to get a standard workflow set up. Having the sequencer outputs normalled to the Sequential Switch inputs, and the switch output normalled to the auxiliary input (#4) of the oscillator CV selectors was an obvious one. The beauty here is that if you insert a cable into the normalled jack, its signal replaces the normalled signal, so you don't lose any functionality or flexibility, you just need less patch cables (depending on your workflow).
These earliest changes to my Moog were all fairly simple mods, but they made subsequent gigs much easier, and they all still function well today, some 30+ years later.
As time went by and I got to know the system better, there were other mods that helped unlock even more potential in this wonderful instrument.
I'll talk about some of those a bit later.
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