Hand built prototypes...

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Hand built prototypes...

Post by noddyspuncture » Sat May 24, 2014 8:47 am

Hi guys,

As I cannot upload photos here - I have also posted this on the Muffwiggler site - and included the link to that here:

http://www.muffwiggler.com/forum/viewto ... 26#1568326

Basically it's a couple of interesting Moog "prototype" items that came along with my R.A. Modular last year...

One is a circuit inside a 901b VCO case - but it seems to have a few components missing. Would love to know what it was made to do. Only the SINE output socket is wired.

The other is in a VCA casing - and there are tell-tale labels on the front. I have powered this one up and plugged in a mic. It does pitch change and has a kind of vocoder-ish effect on the various outputs.


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Re: Hand built prototypes...

Post by CZ Rider » Sat May 24, 2014 2:36 pm

Those are some interesting modules there Tom.
My guess:
The 901 module looks to have been intended for a different purpose. Looks unfinished/repaired/experimental. The connection to the sine output looks to be only getting ground from that socket tab. So no socket on the front panel is wired to anything, suggesting is was at one time left unfinished.
The only connections other that getting the standard power +12/-6/GND is there are three wires going to the edge card connector. A green wire, probably the input and two wires comming from the dual ganged panel mounted potentiometer. (yellow and white with yellow stripe.) The one side of the board looks to have a precision CV adder. With what looks like a MC1439 op-amp. This section of the module looks to be functional. Can see the adder op-amp and precision resistors and a few transistors with some trimmers.
It could be this was an unfinished proto 901?, that was adapted for a different use. Looks like it may have been adapted to be a precision voltage source, perhaps to shift the outputs of oscillators. Could have had the keyboard/linear controller output run through this module to give it a range switch. Moog would usually, but not always, wire those edge card between modules to the same numbered tab. Were there any nearby modules with the wires from those three tabs connected to anything? That would be the best clue as to the function of this particular module.
But my best guess is this was an abandoned module that was converted and made a use for, probably using the adder section for CV purpose.

The other module is quite interesting indeed. That looks to be a Moog pre-amp, much like the one found on the Minimoog external input. Missing the overload indicator circuit though. Moog made a few of these modules and I am not aware they ever assigned a module number to them.

What is interesting is there is added circuitry for the 8va and 16va labled outputs. Could be this is a sub-octave generator, giving one and two octave output below the input. Or it could be some type of octave filter. Tough to tell from those low resolution photos. There look to be three seperate circuits. One simple amplifier circuit and two more complex similar but differently tuned circuits. On those cap filters you can see a few tagged on resistors/cap indicating this was tuned/selected to get the proper response. Might be similar to a octavider type circuit. Certainly worth experimenting with and possible reverse engineering. See what happens with a sine wave input on a scope from the different outputs. This will tell you what it is doing.
Very interesting Moog module. I would not mind having an R.A.Moog discrete octavider to build.
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Re: Hand built prototypes...

Post by Casper » Fri May 30, 2014 6:33 am

My DIY synth:

Fento Synth Version 2.6

A simple analog synthesizer using Arduino.
The encoders are used to configure and set the operation mode.

There are 4 modes:

Mode 0 - normal operation - receive external data (MIDI).
Mode 1 - setting mode.
Mode 2 - Generate notes without the use of external input.
Mode 3 - Mini internal sequencer (just for fun).

The code is in the development stage, but works.


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