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Moog Rogue Trim Pots

Tweaking your Moog Rogue

Disclaimer: Use this information at your own risk. If following this advice causes your Moog to emit purple smoke, it's your own fault, unless you think that's cool, in which case it's still your own fault.

Have you ever wondered what the nine trim pots on the back of a Moog Rogue are for? I did, and so I did some experiments to figure it out. Since there isn't any information about this on the web, I decided to write up my results. The information in this document is purely the result of my own research; I have never seen the Moog service manual.

(In the time since I originally wrote this, I came across some more information about adjusting the trimpots, at: http://elists.resynthesize.com/analogue-heaven/1999/07/271757/. You might want to refer to that information too.)

Across the back of a Moog Rogue, you'll find nine trim pots. I only was able to figure out what eight of them did; the ninth one (near the power switch) seems to have some vague effect on tone or volume, but I have no idea what it really does. I will refer to the others as 1 through 8 as shown in this photo:


As best as I can discern, these trim pots function as follows:

  1. Keyboard control voltage adjustment
  2. Octave switch range
  3. Oscillator 1 pitch
  4. Oscillator 1 range
  5. Oscillator 2 range
  6. Oscillator 2 pitch
  7. Oscillator 1 keyboard tracking
  8. Oscillator 2 keyboard tracking

Notes about these adjustments:

1. Keyboard control voltage adjustment

This adjustment allows you to adjust the voltage output range of the keyboard, and should be the first thing you tweak. To measure it, connect a cable to the "keyboard in/out" jack on the back. Like the panel says, be sure you use a stereo (tip-ring-sleeve) plug. I find an insert cable handy for this. Using a voltmeter, measure the voltage between the tip and the sleeve. The voltages should be as follows:

    Low F	0.000 V
    Low B	0.500 V
    Middle F	1.000 V
    Middle B	1.500 V
    High F	2.000 V
    High B	2.500 V

The low F voltage remains fixed, all the other voltages change as the trim pot is adjusted. You probably won't find a setting that exactly hits the right values at every point on the keyboard; aim for the setting that gets the closest overall.

2. Octave switch adjustment

This pot controls the spacing between the octaves as selected by the octave switch on the front panel:


Initially set the switch to 32', as this setting is unaffected by the trim pot. Turn on just Oscillator 1 and get a reference note in tune, using some combination of the pitch bender, the tuning knob, or the other trimpots. Then, with the switch in the 16' and 8' positions, adjust the trim pot until all three octaves are in tune.

3. Oscillator 1 pitch / 6. Oscillator 2 pitch

I think this is a straight pitch tuning adjustment for each oscillator. Before tuning the oscillators, set the tune knob straight up and the interval to "unison":

http://www.cliffmccarthy.net/images/moog_rogue/moog_rogue_tune.jpg http://www.cliffmccarthy.net/images/moog_rogue/moog_rogue_interval.jpg

The range covered by the trim pots is quite large---about an octave. If you find that you are having to turn the pot to its limit to get anywhere near the right note, your pitch bender may be out of adjustment. The pitch bend wheel is held in place by a set screw that is accessed through the hole in the finger notch at the crest of the wheel. Use an allen wrench to adjust it. (You'll have to guess at the size.) If you center the pitch trim pots then turn the pitch bender until you hit approximately the right pitch, you can then loosen and re-center the pitch bender. Make sure you can still turn the wheel through its full range without hitting the limit of the pitch bender pot. Once the bender is approximately in the right place, adjust the oscillator trim pots again.

4. Oscillator 1 range / 5. Oscillator 2 range

I'm not exactly sure what the relationship is between these pots and 7 & 8. My guess is that 4 & 5 are adjustments internal to the oscillators, while 7 & 8 control the degree that the keyboard control voltage affects the pitch. To get these in tune, check notes across the whole range of the keyboard. Tune a low note using trim pot 3 or 6 (depending on the oscillator), then check a high note and adjust this trim pot until the high note is in tune. Then go back to the low note, which may have drifted a bit, and adjust trim pot 3 or 6 again. You will probably have to iterate this process a bit until you hit the right combination. When everything is adjusted correctly, you should be able to play both oscillators in unison across the whole keyboard without them "beating" anywhere along it.

7. Oscillator 1 keyboard tracking / 8. Oscillator 2 keyboard tracking

I'm not sure how tweaking these is different from tweaking 4 & 5, so you're on your own here.