Moog Modular Restoration

By Mike Borish July 2016

This synthesizer was commissioned by Roosevelt University and built by R.A. Moog, a leader in the field of electronic music instrumentation, in the fall of 1967. This article highlights the dilemmas I was faced with while restoring one of the earliest versions. Most readers will recognize the Moog name, and these modules might appear similar in design to those currently in production, but many similarities end there. When this system was built, the cabinet control panels, wiring, and modules were at the beginning of a long transitional state and had not quite reached the maturity found in later systems. Some fans might argue that this lack of maturity or instability is what defines the classic Moog sound. Moog’s objectives changed too over the years as well as musician’s preferences for different models. This is basically one of the earliest known systems and could have been one of the largest at the time it was commissioned. Who would have thought that an instrument creating poor emulations of other instruments would take on a following of its own and set the groundwork for an entire musical culture?

Restoring or conserving this system was a big task. Experts will always disagree on how far to take things, what should be done, and what should be left alone. In essence, restoring a system like this is a combination of history lessons, electronic theory, and practical experience. Preserving what made these early Moog systems a classic is not a simple task. What complicates things even more, is that this collection of components is modular and highly modifiable. A previous professor really did a number on it with all sorts of cabling as you can see in the photos. When I started this project, the system was totally in disrepair. Obviously, I had my work cut out for me.

The first step I took in tackling these problems was collecting info. Unfortunately, Roosevelt no longer has in its possession information related to this equipment. I contacted Dan Wyman, author of the Moog Modular Owners Manual, and he was very helpful. Dan suggested I listen to to the Nonesuch Guide to Electronic Music for an idea of how this system is supposed to sound and offered me lots of insight regarding the objectives of Bob Moog at the time. Reverse engineering the cabinet layout and other equipment in the Roosevelt collection helped out too. Another good source of information was the internet. After uploading pictures and asking around, I found two other systems from exactly the same time period. I found a basically intact system that used to be owned by Mickey Dolenz of The Monkees, and photographs of it helped me out immensely with deciding on the current module layout.

The second steps that I took were fairly straight forward, and I decided to put off the difficult stuff till last. All electronic equipment has a finite lifespan. Replacing electrolytic capacitors that are subject to serious degradation and frequent failure from aging were the first things to come out. I also replaced parts that had been subjected to mechanical wear and tear, frequent usage, etc. Some switches went bad and needed to be replaced, some potentiometers were very scratchy, etc. I replaced the power supplies with modern equivalent supplies.

Drifting components, components that have changed their electrical values and are no longer in tolerance, gave me lots of stuff to think about. It wasn’t that they were hard to locate or fix, it was the sonic qualities that resulted from a change in their values. In other words, I had a lot of trouble determining if some bugs were actually a feature and if I should tinker with them. I can easily argue that a “broken in” Moog system is similar to an unmolested Blackface Fender Super Reverb guitar amp. Everyone knows that a vintage amp sounds different after you replace the speakers, tubes, caps, etc. I’ve met several musicians that would rather not fix their gear unless smoke comes out of it because they don’t want to lose the sound. Obviously, it is necessary to balance functionality dependability, and safety with tone. But, is an early Moog supposed to drift out of tune occasionally? Sure! Are idiosyncrasies found in different modules important or should I make them all totally uniform? These were just some of the important questions I had to address.

Many critical functions in the Moog modules are the result of an interdependent relationship among precision components. In my opinion, this interdependent relationship is what defines the Moog sound and what makes every Moog module sound slightly different. The 901 modules are a great example of this. Each oscillator footing requires a hand matched bundle of components to create a certain pitch at a specific control voltage. Changing these around is a big can of worms that can alter your scaling, shape of your output waveforms, and amplitude. Also, Unlike the 921 oscillators which are based on operational amplifiers and are far more disciplined, the 901B’s are relaxation oscillators, based on unijunction transistors, and are subject to their own special kind of pitch drift and scaling issues. 901’s are tuned differently too. Are all of these wild irregularities a feature or a bug? Who knows, but they sure are fun to listen to. Another example is the resistors that determine the shape of the output waves from the oscillator modules. There’s a guy I met on the net that really dialed these in to textbook wave shapes. My attitude is that if I wanted textbook waveshapes, I’ll get a Eurorack system.

There are several features that set the early Moog oscillators apart from the later ones. These early 901A’s have low compensation, mid high compensation, and high compensation as well a a general scaling potentiometer for calibration purposes. If you play all of the keys in sequential order, this outputs some wicked volt / octave ratios. The tuning on the oscillators is equally complicated. The 901B oscillators are matched to the 901A by trial and error. It is possible for an oscillator to be in tune for an octave, drift for the next, and then be in perfect tune for the duration of the scaling. Tuning is part science and part gut instinct.

This early Moog design is also the first to employ the famous 904 transistor ladder filter too. The 904 design is probably the most famous patent in all of electronic music. It has been copied and modified by just about every other synth manufacturer since it’s inception.

Revisions and upgrades are a big and difficult problem and probably gave me the most grief. Cabinet interfacing was a huge issue. Some of the modules don’t have DC blocking capacitors and are subject to drift and offset. Impedance matching amongst components is awkward with some configurations. The system wasn’t set up for computer interfacing either and I made some modifications to accommodate modern studio technology.

In conclusion, my philosophy is to alter the synth as little as possible with respect to the original intentions of the designer. I employ modern techniques and components. To that end, I examine everything closely and tailor my methodology to meet both the needs of the synth, and the client. My work is generally non invasive, meaning almost all of the work I do is reversible.

I strongly encourage everybody to check out this awesome system at Roosevelt University in Chicago if you can. It’s really something special and an important piece of musical history.

Part of Roosevelt System

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