Vintage Synth Repair

Hey guys. 

I picked up a Moog Source yesterday. And of course, it doesn't work properly. 

The synth is in perfect cosmetic condition, with a beautiful membrane panel. It's firmware 3.3.

The problems so far consist of:

Oscillator 2 works. Oscillator 1 does not. The waveform buttons for osc 1 make slight clicks, which seem to sort of change tone over time.

Also, the keyboard intonation is wacky. In order to get an octave, you basically have to play a flat 9. So in order to play C1, then C2, you have to play C1, then C#2. 

Suggestions? Opinions?

Thanks!

Jim

Sounds like you need to get a copy of the service manual and go through that first. You don't really need a oscilloscope to make the adjustments, just a good ear and another well-tuned synthesizer as a reference.

Fortunately it sounds like you aren't having the "Crazy Source" problem, but you might as well look into that while you have it opened up. It's a bit like a can of snakes, so my best advice is to take good high-resolution photographs of the disassembly (or find  someone else's) and take it slow and easy.

The Source is pretty complex on the inside due to all the digital stuff they had to squeeze in, but it's all easily repairable once you figure out where everything goes. Calibration will fix your tuning problems, and possibly some of the other issues too. Once you get there, I'm sure you can get a lot more help on this list with whatever is left, and have enough experience with it to understand the additional advice you can get here.

Good luck and congratulations on getting such a classic synth! -pc

P.S. These will get you started:

http://thesnowfields.com/manuals/Source_Manual.pdf

http://thesnowfields.com/manuals/Source_Service.pdf

On Jan 11, 2013, at 8:01 PM, z z wrote:

> Hey guys. 
> 
> I picked up a Moog Source yesterday. And of course, it doesn't work properly. 
> 
> The synth is in perfect cosmetic condition, with a beautiful membrane panel. It's firmware 3.3.
> 
> The problems so far consist of:
> 
> Oscillator 2 works. Oscillator 1 does not. The waveform buttons for osc 1 make slight clicks, which seem to sort of change tone over time.
> 
> Also, the keyboard intonation is wacky. In order to get an octave, you basically have to play a flat 9. So in order to play C1, then C2, you have to play C1, then C#2. 
> 
> Suggestions? Opinions?
> 
> Thanks!
> 
> Jim

The first thing I check on a Source is this - 

http://www.synthfool.com/docs/Moog/crazysource_mod.jpg

Doug 
synthparts.com

--- In vintagesynthrepair@yahoogroups.com, "z z"  wrote:

>
> Hey guys. 
> 
> I picked up a Moog Source yesterday. And of course, it doesn't work properly. 
> 
> The synth is in perfect cosmetic condition, with a beautiful membrane panel. It's firmware 3.3.
> 
> The problems so far consist of:
> 
> Oscillator 2 works. Oscillator 1 does not. The waveform buttons for osc 1 make slight clicks, which seem to sort of change tone over time.
> 
> Also, the keyboard intonation is wacky. In order to get an octave, you basically have to play a flat 9. So in order to play C1, then C2, you have to play C1, then C#2. 
> 
> Suggestions? Opinions?
> 
> Thanks!
> 
> Jim
>

I just picked up a second ProSoloist (kind of third, if you count the 
ProDGX). This one sat in a closet for 40 years, then restored. 
Perfect condition. Except for one thing....

Both of the "Fuzz Guitar" presets behave oddly. It seems like they 
sort of "cycle through" slightly different waveforms. Sine, square, 
saw, etc. Abruptly, almost like someone reciting vowels. also, Fuzz 
Guitar 1 is kind of quiet, while Fuzz Guitar 2 is really loud.

Everything else is great.


Any suggestions?



Thanks,

Jim

Both of the "Fuzz Guitar" presets behave oddly. It seems like they
sort of "cycle through" slightly different waveforms. Sine, square,
saw, etc. Abruptly, almost like someone reciting vowels. also, Fuzz
Guitar 1 is kind of quiet, while Fuzz Guitar 2 is really loud.

Could be normal behaviour.

I recall from several Pro-Soloist and Pro-DGX that there was a very
noticeable difference in loudness between both Fuzz Guitar presets.

As far as the "stepping" of the waveforms goes: This is probably also normal.

Both presets (and a few others) use the "dynamic pulse" setting;
essentially the  implementation of PWM for the Pro-Soloist. The "dynamic
pulse" is derived from the sawtooth wave.
The following is from memory: I recall the sawtooth not being a "smooth"
sawtooth but a stepped one (because it's actually built out of a number of
pulse waves with different pulse widths). On the oscilloscope it looks like
a real staircase. So if this wave is "scanned" by the ADSR there naturally
will be some stepping.