MG1 lower octave mod?

[Tomas]

Ive seen some MG1s that have been modded to go down an extra octave lower on osc 1. Does anyone know how that is done?

Thanks

[thealien666]

Hello and welcome to the forum Tomas.

I'm not aware of that mod. But I remember that, back when I had my MG-1, I lowered the polyphony pitch by one octave to better match the range of the two tone sources. It's a simple trimpot tweak adjustment inside the machine on the lower board, the one identified as "Poly Freq Trim".

[Gladmarr]

Ive seen some MG1s that have been modded to go down an extra octave lower on osc 1. Does anyone know how that is done?

Thanks

I know I've controlled my MG-1 with a voyager and played way lower than the MG-1 keyboard would allow, so the internal oscillators will go lower than the MG-1 internal keyboard will allow. So it can be done. You could probably change the voltage ranges for each switch setting, or change the switch to something that allows four octaves instead of three. I don't know exactly how to do it, but just based on voltage range it is possible.

[thealien666]

Having had a look at the schematics, I would replace R4 and R5 (currently 1Meg 1% matched) with two, 2Megs 1% matched resistors. That should bring Tone Source 1 down a full octave. So the octave switch would have a new range -1, -2, and -3, instead of 0,-1,-2 original range.

But those resistors would absolutely have to be matched precisely. And , you might have to recalibrate Tone Source 1 after the mod.

Alain.

Note: this is theoretical based on the schematics around the octave range switch, by logic deduction. This is offered as a potential mod. Since I didn't try it, there's no guarantee that this will work as described, but it should. If it doesn't (which I doubt) you can always re-install the original resistors... Also, since all the components are on the top side of the panel board PCB, you will have to remove it, in order to perform the mod (removing all the sliders caps, and knobs, and a few screws holding the board up).

To help you locate R4 and R5, they are the light blue ones to the left of the rectangle marked SW1 in the lower left pic:

[stiiiiiiive]

So the octave switch would have a new range 1, -1, and -2, instead of 0,1,-1 original range.

Alain, you meant 0, -1 and -2 as new range setting, didn't you?

[thealien666]

I got my ranges all mixed up...

The actual ranges are: 0, -1, -2
The new ranges should be : -1,-2,-3

The octave switch connects the two original 1M resistors from the +12 V supply either:
two in parallel: 0 range
only one: -1
two in series: -2
going to the CA3046 pin 5.

Thanks for spotting my mistake..
(I edited my last post to correct the mistake and avoid any confusion)

[Tomas]

Thanks for all the responses guys

lm not much experienced in electronics, but just thought id ask in case there was a way to do it w/o any soldering or anything like that.

Gladmarr mentioned he went down lower when playing the MG1 with his Voyager keyboad. So perhaps a simple cv/midi converter, using an external full range keyboard is all thats needed?

Also, does anyone know how the 0, -1, -2 ranges of the MG1 correspond to the standard footage ranges? Like is -2 equal to 16', -1 equal to 8' etc?

[thealien666]

I think it's:

-2 = 16'
-1 = 8'
0 = 4'
+1 = 2'

[Gladmarr]

Gladmarr mentioned he went down lower when playing the MG1 with his Voyager keyboad. So perhaps a simple cv/midi converter, using an external full range keyboard is all thats needed?

I just ran a CV cable to control pitch, but you also need to be able to convert standard V-trigger to S-trigger for the MG-1, some more old-school analog weirdness.

I have saved a bunch of pages listing MG-1 mods over the years, these might help you:

http://www.cykong.com/Synths/Moog%20Rea ... 1-Mods.htm

http://www.flickr.com/photos/pablopenas ... 119094427/

http://machines.hyperreal.org/manufactu ... .input.txt

[Tomas]

I think it's:

-2 = 16'
-1 = 8'
0 = 4'
+1 = 2'

Thanks

[Tomas]

....

[Tomas]

Gladmarr mentioned he went down lower when playing the MG1 with his Voyager keyboad. So perhaps a simple cv/midi converter, using an external full range keyboard is all thats needed?

I just ran a CV cable to control pitch, but you also need to be able to convert standard V-trigger to S-trigger for the MG-1, some more old-school analog weirdness.

I have saved a bunch of pages listing MG-1 mods over the years, these might help you:

http://www.cykong.com/Synths/Moog%20Rea ... 1-Mods.htm

http://www.flickr.com/photos/pablopenas ... 119094427/

http://machines.hyperreal.org/manufactu ... .input.txt

Ive been thinking of getting a Microbrute which has CV I believe. So would I be able to play the MG1 using the MBs keyboard, connected via CV, and then have access to the lower octaves on the MG1 oscillators that way?

Also, would this cable work as my S/trig to V/trig converter, and would that be all Ill need, if so?
http://www.ebay.com/itm/KORG-MS20-mini- ... 1e803ba779

[Gladmarr]

I think that cable would work. Not 100% sure. Hopefully someone here knows more about the conversion than I do. You'll certainly be able to control pitch - it's the gate/trigger that needs the conversion and might be tricky.

[thealien666]

Yes that cable should convert Gate signal (or pulse) into S-Trigger (meaning Short to ground Trigger). It's a very simple device with one resistor and one transistor as shown below:





The Pitch CV will be something else. In the world of analog synths, although the specification says 1 Volt per octave, the Pitch Control Voltage is not always precisely 1 Volt per octave from one machine (manufacturer) to the other. That's one of the main reasons why MIDI was invented to alleviate these annoyances.

One thing for sure: the Microbrute WILL play the MG-1 (with the S-Trigger adapter), but the MG-1 may not track pitch correctly across the whole keyboard range (an outside).

BTW, even though the MG-1 circuits show that it expects an S-Trigger note triggering signal, I've used my Boss DR-110 drum machine with it for many years, even though the DR-110 output a +5 Volts positive trigger out (not an S-Trigger out), and the MG-1 still played fine with it; a note would be heard (played) by the DR-110 on each pulse it sent.

[Tomas]

Yes that cable should convert Gate signal (or pulse) into S-Trigger (meaning Short to ground Trigger). It's a very simple device with one resistor and one transistor as shown below:





The Pitch CV will be something else. In the world of analog synths, although the specification says 1 Volt per octave, the Pitch Control Voltage is not always precisely 1 Volt per octave from one machine (manufacturer) to the other. That's one of the main reasons why MIDI was invented to alleviate these annoyances.

One thing for sure: the Microbrute WILL play the MG-1 (with the S-Trigger adapter), but the MG-1 may not track pitch correctly across the whole keyboard range (an outside).

BTW, even though the MG-1 circuits show that it expects an S-Trigger note triggering signal, I've used my Boss DR-110 drum machine with it for many years, even though the DR-110 output a +5 Volts positive trigger out (not an S-Trigger out), and the MG-1 still played fine with it; a note would be heard (played) by the DR-110 on each pulse it sent.

Thanks for all the help. Id only need to use the Microbrute to control it for deep basslines, so even if it doesnt track pitch accurately across all octave ranges, if its good across just that 1 octave on the low end that would be enough. I can just use the MG1 keyboard for other octaves.