Moog/Realistic MG-1 Mod Guide

[facon]

Here's a quick drawing. The two 120K resistors are already on the PCB. You just need to add the wires from one side of R28 and R2 to the center poles of the switch. Then wire the 169K resistors from the top pins to the other sides of R28 and R2.

There are some switches that are laid out differently. Now is a good time to learn a little more about what that switch is doing. Take a multimeter and put it on the resistance setting (will be an ohms symbol). Run a continuity test on the pins. Some multimeters have a button you can press to play a sound when there is no resistance between the two probes. You should see when the switch is in one position, the middle two pins connect to the pins on one side. When it's in the other position, the middle two pins connect to the opposite side. Pretty simple!

[Alrod]

Awesome, it makes perfect sense now. Thanks so much for taking the time to do this!

[nebula]

Here is a demo of all the new stuff:
https://www.youtube.com/watch?v=QuztPaTRY9Q

And here is a demo tune only using my "new" MG1:
https://www.youtube.com/watch?v=li2joEBwFgw

Incredible work, and it sounds really great. 3 questions pop into my head:

How did you make such nice panel legending?
What did you use to cut the nice square holes for your slide switches?
What did you mount the slide switches to??

I'm definitely going to take on some of these mods, but I want it to look as great as yours!

[facon]

Hi, first of all - thank you Falcon for posting all these tips - they really worked great and I have done almost all of them (and then some extra), and my MG1 has turned out awesome!

Here is a demo of all the new stuff:
https://www.youtube.com/watch?v=QuztPaTRY9Q

And here is a demo tune only using my "new" MG1:
https://www.youtube.com/watch?v=li2joEBwFgw

There is a few additions, the multi trig-circuit needs to have a 90k at R7 for better multi-triggering.

When doing the LFO -> osc2 pitch, it is easy to put in a switch and then tap the ENV-signal from pin7 if the U13 op-amp. Then you get FM on the osc2 from both LFO and ENV.

Then you can use the same set up, but instead of going to the osc2 pitch, you plug it in to the PW's. Then you get switchable PWM either from LFO or ENV.

There is also a 10k trimpot for adjusting the Cut Off, put this on the panel as well so you can close the filter to zero.

Thanks again, Falcon!

How'd I miss this? Great work!! The replacement vinyl faceplate is a really nice touch.

[Lackan110f]

Thanks guys! I love my MG1, and as you can see on the faceplate it is now a MOOG for real. I decided on putting the Moog-name bigger. Since it says Moog on the boards anyway. Apparently, the original name-suggestion was "Moog MIDGET" but Realistic decided on MG1.

@nebula; to answer your questions:
1) It is a rugged vinyl printing. Costed me abour €50. Alas I did not realize that some of the pot's had wider shafts, so it ended up being a bit of a patchwork having to drill larger holes, but you only notice when you look close.
2) I used a 4 mm drill, made two holes, and then used a fine metal file (bought really thin ones) to file it open between the holes. Again, if you look close it is not perfect, but from an arms distance you won't notice.
3) The trickiest part. They are actually all mounted with screw and nut. I used the smallest size I could find, then I filed the head of the screw flat (so it would create a large flat surface) and then I super-glued it to the metal from beneath. Then i attached the switch with the nut. Really tricky but it worked. And - touch wood - they are all still in place.

Here is a thread on a swedish music-forum where I posted all my work in progress, here you can see some images as well:
http://www.99musik.se/showthread.php?32 ... tora-modtråden

And as a final twist, I slaughtered an old beat up Kenton ProSolo mk1 and put it inside the right end-cheek. Fitted perfectly, and it is by far the best Midi-CV ever made. So now I have velocity-to-VCF and an extra LFO in my "MOOG MG1" as well.

PS; I'm not normally in favor of modding vintage gear this heavily, but I got my MG1 really cheap with a smashed right end cheek and cracked surface sticker. So it was a mess anyway. And I must say that considering that it is now one of my favorite synth (use it more than my Minimoog actually) it is really worth doing all these mods. To get such a monster synth in such a small format is great!

Thanks again Facon, all creed goes to you!!!

[lordradish]

It should take around 10 to 15 minutes if you're already disassembled. You can find the procedure on page 18 of the manual: http://manuals.fdiskc.com/flat/Realisti ... Manual.pdf

A lot of DMMs have a frequency reader that you can use. A frequency generator will also do the trick. Otherwise you can use a tuner. I think I just used my Cleartune tuner app to calibrate it. For example, 660 Hz is E at 5 semitones: http://en.wikipedia.org/wiki/Scientific_pitch_notation

If you're having problems calibrating because of the emphasis pot, you'll know that something isn't right. Regardless you should check all of your solder joints to make sure everything is good.

If everything is done correctly, is recalibration generally never needed when doing the filter mod? I just got my MG1, want to do the filter mod, but I'm having a very hard time understanding that calibration process on p18. I'd hate to do it and be stuck.

[facon]

If everything is done correctly, is recalibration generally never needed when doing the filter mod? I just got my MG1, want to do the filter mod, but I'm having a very hard time understanding that calibration process on p18. I'd hate to do it and be stuck.

You sent a few questions through PMs and in other threads. I'm just going to respond to them here. Just in case other people have the same questions.

There are three main calibration procedures in the manual. Tuning calibrations for all three sound sources (poly, osc 1, osc 2), setting the range of the filter pots (scale, emphasis, and cutoff), and adjusting the final VCA output volume. I would skip the square wave adjustment unless you have an oscilloscope and want it to be perfect. They can be found on pages 17 and 18 of the manual:

http://manuals.fdiskc.com/flat/Realistic%20MG-1%20Service%20Manual.pdf

You should go through and calibrate the tuning if you are modifying any of the oscillators. In the manual, whenever it says trim next to it, that means its a small internal trim pot. They're little plastic pots that you use a screwdriver to turn. I think for the oscillators, these trim pots are also reachable from the back through some small holes. For example, to tune oscillator 1, there are three trim pots that the manual tells you to center (Tone Source 1 Freq Trim R1001, Tone Source 1 Scale Trim, R1008, and Tone Source 1 High Freq Trim R1009.)

These steps are important because you want to make sure the tuning range is set correctly. If not, your oscillator will go out of tune every time you switch an octave. Or will be in tune on the lower notes, but out of tune on the high notes. The process is really simple as long as you have a tuner that you can plug it into. Some of the directions tell you the specific tuning octave by specifying the actual hertz. 440hz is A and is generally what the A directly above a middle C on a piano is tuned to. If your tuner doesn't tell you the exact frequency, you can probably use a app for it on your phone.

The filter tuning is important so that the settings will all react like you expect them to. If you modify the filter, you'll definitely need to go back and adjust the trim pots. Just follow each step, one at a time, in the manual. Most of the settings are "close enough". Just to get you in the range so that it will self oscillate correctly.

The filter components are all located on the top board. They are mostly in between the Contour and Master Volume.

[lordradish]

Awesome, this is very helpful, thank you.

[elisavage]

Hi there, I know this is an old thread, but do you still have the photos that were hosted on photobucket? I am going through and trying to do the mods, but it would e easier if I had the images you so kindly made/posted too.
This is super exciting, thank you for the time and effort put in.
Thanks,
Eli

[Helfried]

Hi, thank you for all the great, useful information!
At the moment i'm trying to build the retrigger mod, but cant get it to work until now. It does strange things here, sometime triggering by itself, sometimes triggering OK and sometimes nothing. The keyed mode is also not working with my mod installed.
I removed it for now - maybe i'll start again from scratch.

I have one question (maybe this belongs to my problem with the mod): Is it normal for an unmodded MG-1, that in contoured mode (with sustain out) fast note-repetitions and fast playing (non legato) in general is impossible? Slow staccato notes are working, but when playing faster (even short staccato with gaps between the notes) the envelope is not starting again.
Could this be a fault on my MG-1 ?
Maybe there is something wrong with the contour generator or the triggering ?

[Helfried]

I answer myself now
My second problem - the slow keyboard response and unability to play staccato nots - is solved.
I simply lowered R47 to speed up the discharging of the parallel capacitor to ca. 80k - voila !

But the retriggering mod is still not working.
I doublechecked all the wiring, replaced the 1μF capacitor with a film capacitor, but still no success.
It works a bit better now, it is retriggering if the distance between the notes is high (more than an octave) , and it retriggers only in one direction: playing low notes simultaneously to held high notes does not work, the other direction works if the the distance ist large enough.
does anybody have experience with that mod ?
any ideas ?
thank you very much !

[Helfried]

OK, here comes part 3 of my monologue.
the good news:
I think that now everything works as it should.
The problem, that the retriggering functioned only with larger note distance, was due to the fact that in the diagram on page 1 of this thread a wrong value for R2 is drawn. R2 should be 10k and not 100k (as in the original Ricard Wolf circuit - http://machines.hyperreal.org/manufactu ... ig.mod.txt).
with the smaller value for r2, retriggering now works.
However, with the following restrictions:
- Due to the High Note Priority multitiggering works logically only in one direction
- Also when releasing a key is re-triggered, as long as other keys are pressed

This feels strange when playing, you have to get used to it.

It has now become clear to me that it has to be this way and that it can not be otherwise. I'm not sure if I want it that way. Maybe I just keep the Continous Glide Part - and leave the synth in single trigger mode.
But it would be good if the schematic on page 1 were corrected (R2 = 10k)