Moog Concertmate MG-1 Mods

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facon
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Moog Concertmate MG-1 Mods

Post by facon » Wed Jan 28, 2015 8:53 am

EDIT: Posted on the moog forum - http://forum.moogmusic.com/viewtopic.php?f=1&t=22856


I'm getting pretty close to finishing up on testing all of the mods I have listed for the MG-1. My goal is to post a comprehensive guide on how to mod this synth. Is there anything I'm missing on my list that anybody would like to see?

PERFORMANCE MODS
Minimoog Filter mod - Increase filter coupling cap values, lower input impedance and change filter cap and resistor values to match Minimoog
Add continuous glide and re-trigger circuit to keyboard tracking (stripboard layout provided)
Replace 5837 Noise chip with analog noise generator (stripboard layout provided)
Tune Osc 1 & 2 one octave lower
Osc 2 Detune slide pot to full octave up and down
Increase filter modulation level
Increase audio output level
Change Ring Mod input from Osc 1 square only to post-switch/pre-mixer Osc 1


ADDITIONAL FUNCTIONALITY MODS
Add Sustain pot
Osc 1 and 2 PWM pot
Osc 2 Detune/pitch modulation pot (very cool flanger meets autowah effect with sync in!)
Poly pitch modulation pot
FM pot
VCA modulation pot
LFO speed switch (fast, normal, slow)
Osc 1 octave up switch
Ring Mod carrier from LFO (instead of Osc 2 Square) switch
Internal or External switchable Saw to Triangle to Sine convertor (stipboard layout provided)
Internal or External VCA ASDR (stripboard layout provided)
Separate headphone and master volume pots

BACK PANEL CONNECTIONS
CONTROL VOLTAGE:

VCA
VCF
Envelope
V-Trigger
Gate
LFO In/Out
Keyboard In/Out
Sync In

AUDIO:

Post Filter/Pre-VCA In/Out
Pre-Filter Audio In
Noise In/Out
VCO
Osc1 - Pre-mixer
Saw In/Out
Osc1 Post-Switch In/Out
Osc2 - Pre-mixer
Saw In/Out
Osc1 Post-Switch In/Out
S&H In
Poly Pre-mixer In/Out
Ring Mod Audio In
Ring Mod Carrier In
Last edited by facon on Wed Feb 18, 2015 8:44 pm, edited 4 times in total.

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c1t1zen
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Post by c1t1zen » Wed Jan 28, 2015 10:22 pm

I would love a guide for all this, I have an MG-1 that is defoamed and waiting mods!

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Post by 3vcos » Wed Jan 28, 2015 10:56 pm

Where's Paul Schrieber? Let's all boycot buying MOTM until writes a complete guide to modding an MG-1 to these specs. :party:

facon
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Post by facon » Thu Jan 29, 2015 10:41 am

c1t1zen wrote:I would love a guide for all this, I have an MG-1 that is defoamed and waiting mods!
Cool. I just have a few more to finish up and test. If you have any specific questions about a particular mod that you'd like to get started on, I'd be happy to send over any details.

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cleaninglady
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Post by cleaninglady » Thu Jan 29, 2015 5:02 pm

Watching this thread with great interest. :domodance:

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Post by calaveras » Thu Jan 29, 2015 5:15 pm

I just recently bought one of pretty much every part in my MG1 so I can refurb it up to factory new specs. (well not all the chips obviously).
I'll be checking out some mods for it once I get it to stock. Mostly to fix it's note triggering problems.
I was already going to build in an S-Trig to gate converter and do something more professional on the output and the headphone jack.
The ring mod is just a digital XOR right? Is there any reason we cant get the poly voice in there?

facon
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Post by facon » Thu Jan 29, 2015 5:41 pm

I don't see any reason why not. Personally, I would use the outputs to connect the poly to the ring mod input. But, if you want to check it out internally without it, the Orange wire that connects to pad 15 is the ring mod input. Desoldered that and connect it to the blue wire that goes to pad 24. Don't desolder that pad or you'll lose the regular Poly. You may need to adjust R50 (or put a pot between the wires) to get the levels matched a little better. I haven't experimented with this yet to try it.

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qp
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Post by qp » Sun Feb 01, 2015 8:50 pm

Looking forward to the details!

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captnapalm
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Post by captnapalm » Sun Feb 01, 2015 9:09 pm

This sounds great! I'd be interested to know which ones work on the Rogue also.

facon
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Post by facon » Tue Feb 03, 2015 6:30 pm

I've tried to post this on this forum, but I keep getting blocked. It looks like I'm including some words that the forum doesn't like?

So, I posted the first draft of the guide on the Moog forum. It's still a work in progress. It can be found at http://forum.moogmusic.com/viewtopic.php?f=1&t=22856

Hopefully everybody has access to it. If you'd prefer to have it posted on here as well, I will contact a moderator to see how to get around being blocked.

calaveras
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Post by calaveras » Tue Feb 03, 2015 7:15 pm

facon wrote:I don't see any reason why not. Personally, I would use the outputs to connect the poly to the ring mod input. But, if you want to check it out internally without it, the Orange wire that connects to pad 15 is the ring mod input. Desoldered that and connect it to the blue wire that goes to pad 24. Don't desolder that pad or you'll lose the regular Poly. You may need to adjust R50 (or put a pot between the wires) to get the levels matched a little better. I haven't experimented with this yet to try it.
I may look into that while I have it apart. I'm actually held up because I seem to have misplaced the box of screws for the ratty Poly61 on my bench right now. If I can get the Korg moved I'll start playing with this as I replace all the faders and some of the caps.

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qp
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Post by qp » Tue Feb 03, 2015 7:34 pm

facon wrote:
So, I posted the first draft of the guide on the Moog forum. It's still a work in progress. It can be found at http://forum.moogmusic.com/viewtopic.php?f=1&t=22856
:sb: :party: :guinness: :omg: :tu: <-- in that order

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Post by calaveras » Fri Feb 06, 2015 1:09 pm

While I'm refurbing my MG1 I have run into pretty much only one part I can't find. You guys are thinking top octave chip, but there is a guy that makes a modern equivalent.
I'm actually stumped trying to find the aluminum toggle swtiches?
I know these are used on some other Moogs of that era, and pretty much any hifi from 1970-1990, so it is cracking me up that I cant find them.
Any one hipper to sourcing than me got a clue?
Last edited by calaveras on Fri Feb 06, 2015 1:36 pm, edited 1 time in total.

facon
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Post by facon » Fri Feb 06, 2015 1:23 pm

Syntaur has them, but they are pricey!

https://syntaur.com/moog_mg1.html

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Post by calaveras » Fri Feb 06, 2015 1:40 pm

yeah, I'd seen that. But if you click on that page right after looking at Tayda for resistors and such, you get a wallet hernia.
Honestly the olde MG-1 seems to be functional in regards to the switches. I just figured while I am recapping and re-fadering, it would be a shame to leave these crusty old black foam drenched switches in the path.

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Post by basicbasic » Tue Feb 10, 2015 10:14 pm

Fan-friggin-tastic!

I've started modding my MG-1 as a way to get the hang of SDIY. So far i've replaced the RCAs (easy), removed the audio out resistor for more volume, added a audio input to filter (easy), CV to filter (easy-ish... see below) and ATTEMPTED a way to override the LFO clock...

So questions (apologies for the noob-ness):
- I suspect I need a resistor as part of the VCF CV input as when I have the cutoff all the way down the filter seems to freak out and even the OSC pitch changes. Maybe my CV signal is too hot? Anyway, some help would be great.
- I added a jack that I thought over-rode the LFO clock in order to trigger the S/H externally but it seems to just add the external clock input to the internal one. I'm guessing I need to use a 'switching jack'? Should I also add a resistor or something?

Thanks,
Jamie

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Post by recompas » Wed Feb 11, 2015 11:22 am

Thanks for this - fantastic resource for what is still one of my all-time favorite synths! I've done some mods on mine but nothing this extensive. Every so often I crack it open and do something else. One of the cooler mods is the routing of the LFO to OSC2 pitch to get those nice sync sweeps!

facon
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Post by facon » Wed Feb 11, 2015 11:37 am

basicbasic wrote:Fan-friggin-tastic!

I've started modding my MG-1 as a way to get the hang of SDIY. So far i've replaced the RCAs (easy), removed the audio out resistor for more volume, added a audio input to filter (easy), CV to filter (easy-ish... see below) and ATTEMPTED a way to override the LFO clock...

So questions (apologies for the noob-ness):
- I suspect I need a resistor as part of the VCF CV input as when I have the cutoff all the way down the filter seems to freak out and even the OSC pitch changes. Maybe my CV signal is too hot? Anyway, some help would be great.
- I added a jack that I thought over-rode the LFO clock in order to trigger the S/H externally but it seems to just add the external clock input to the internal one. I'm guessing I need to use a 'switching jack'? Should I also add a resistor or something?

Thanks,
Jamie
It sounds like you might want to try an attenuator between the CV and VCF. Where are you connecting to the VCF? Most of my experience is by tinkering with what other people have done or grabbing from other synths, so it would take some experimentation. You can try putting a pot in between the CV and VCF by wiring it as a variable resistor to find the value that works for you.

It sounds like you'll want a switching jack (Switchcraft 12A, 112AX, etc). Where are you connecting to the circuit for this?

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Dimitree
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Post by Dimitree » Wed Feb 11, 2015 11:39 am

just wondering, what kind of results does it give to change the carrier or the modulator waveshape in the ring modulation? (in general, not only for MG1)

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Post by facon » Wed Feb 11, 2015 11:48 am

Dimitree wrote:just wondering, what kind of results does it give to change the carrier or the modulator waveshape in the ring modulation? (in general, not only for MG1)
It just gives more options to the ring modulation effect. I viewed it like I was connecting an external ring mod box. If that were the case, I would be able to dictate what waveforms are being sent to it. The results are as different as selecting different waveforms for audio.

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Dimitree
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Post by Dimitree » Wed Feb 11, 2015 11:50 am

thank you, I will try that in my synth (not a MG1 but it uses only square waves for ring mod too)

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Post by basicbasic » Thu Feb 12, 2015 1:13 am

facon wrote: It sounds like you might want to try an attenuator between the CV and VCF. Where are you connecting to the VCF? Most of my experience is by tinkering with what other people have done or grabbing from other synths, so it would take some experimentation. You can try putting a pot in between the CV and VCF by wiring it as a variable resistor to find the value that works for you.

It sounds like you'll want a switching jack (Switchcraft 12A, 112AX, etc). Where are you connecting to the circuit for this?
I'll open her up this week and figure out where I connected the wire to the LFO tempo - I might actually have used a switching jack but haven't wired it up to switch. Thanks for the idea of using a pot to work out how much resistance I need for the VCF CV!

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mad_magician
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Post by mad_magician » Wed Feb 18, 2015 8:10 pm

A question in the DIY forum sent me over here. The "Resistors" you are seeing are likely Capacitors or Inductors.

Typical body colors from that time-frame:

Lime Green = Capacitor
Not Exactly Lime Green towards dark green = Inductor
Aqua = Inductor
Sorta Aqua towards Baby-Blue = Film Resistor
Dark Brown/Tan = Carbon Resistor

Make sure you follow the schematic and any service bulletins when replacing parts!

MM

facon
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Post by facon » Wed Feb 18, 2015 8:21 pm

mad_magician wrote:A question in the DIY forum sent me over here. The "Resistors" you are seeing are likely Capacitors or Inductors.

Typical body colors from that time-frame:

Lime Green = Capacitor
Not Exactly Lime Green towards dark green = Inductor
Aqua = Inductor
Sorta Aqua towards Baby-Blue = Film Resistor
Dark Brown/Tan = Carbon Resistor

Make sure you follow the schematic and any service bulletins when replacing parts!

MM
Wow! They are lime green. I will take that section down immediately! Thank you for the correction.

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mad_magician
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Post by mad_magician » Wed Feb 18, 2015 8:28 pm

do you have a picture of one? I would like to see the color code vs the schematic spec.

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