scratchy sounds comming from my moog/sinewave question

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rick reed
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scratchy sounds comming from my moog/sinewave question

Post by rick reed » Tue Dec 09, 2003 3:51 pm

Hello again to all. I'm still enjoying my Model D I bought 8 months ago, but I have two questions that the old hands out there may have a quick answer for, (1.) I seem to be getting a sort of scratchy, electrical current sound bleeding thru from the oscillators when I have everything turned off-and I have a key depressed. Another site I went to mentioned a problem with their Mini that they had up for sale and said it might be a leaky cap. I have no idea what this means, or if it's the same problem. No biggie, just thought I'd ask.
(2.) Has anybody out there had any experience sending a sinewave generators signal into the oscillator port in the back of their mini? I did and it sounds awsome! Sort of a great ring modulator thing happens... I guess what I want to know is, does this hurt anything (does not seem to be harmful so far) and if one is good, would two be better? Is this too hot of a signal for the thing? Always good to read anyones feedback. I'm just a babe lost in the woods sometimes.

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MC
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Post by MC » Tue Dec 09, 2003 8:32 pm

I seem to be getting a sort of scratchy, electrical current sound bleeding thru from the oscillators when I have everything turned off-and I have a key depressed. Another site I went to mentioned a problem with their Mini that they had up for sale and said it might be a leaky cap. I have no idea what this means, or if it's the same problem. No biggie, just thought I'd ask.
I've had that problem. One or more of the power supply connector contacts on the oscillator board has spread and no longer makes good contact with the PC board. The oscillator boards use a kelvin sensing system for the power supply rails and when any of these loses their connection, the audio for the VCOs will travel down the power rails to the rest of your minimoog through the VCA, even though the audio is off on all the VCOs.

The service manual suggests to short a resistor on the power supply board. THIS IS NOT THE CORRECT FIX! This will DEFEAT the kelvin sensing system for the power rails to the oscillator board and your VCOs will drift worse.

You hace to disassemble the connector, pull out the offending contact prongs, and gently bend them so they are not spread so far.
Has anybody out there had any experience sending a sinewave generators signal into the oscillator port in the back of their mini? I did and it sounds awsome! Sort of a great ring modulator thing happens...
That's the oscillator control voltage input jack. It's for hooking up accessories like ribbon controllers and S&H boxes that the old Moog Music used to sell. You can also hook up MIDI->CV devices for MIDI control of your mini, but it's not ideal. And yup, feeding an audio range sine wave will yield ring-mod sounds.

Vic
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Ring Mod

Post by Vic » Wed Dec 10, 2003 3:31 pm

I have used a Heathkit (old test equipment) sine-square signal generator, and ooh, look out! Currently I use a Krohn-Hite Model 1200 Oscillator, makes c-64esque ring mod sounds, pretty interesting....! I have a couple more 'ome-made white noise gen's and such, I tried Patching them into the 'Audio IN' in a Prodigy, and when the keys were struck, the Moog's internal goodies morphed my audio into something quite galactic... Thanks for reading this banter. Vic

agermani
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Oscilaltor Bleed Through

Post by agermani » Thu Jan 15, 2004 12:08 am

I have the same oscillator bleed through problem that Rick Reed described and was excited to see MC's solution to it. I tried it out, however, and I'm still having the same problem. The connectors should definitely be tight enough to be making a good connection at this point.

Any other ideas? Thanks to MC for pointing out that the solution in the original service manual is incorrect. I would have tried that out in a heartbeat otherwise.

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MC
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Post by MC » Thu Jan 15, 2004 11:02 pm

Check the continuity from the connectors to the PC board itself. The connector will still feel tight even though one of them has pried loose.

agermani
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Post by agermani » Fri Jan 16, 2004 12:28 am

I'm not sure if I understand what you're saying here.

Here's what I did:
I cracked open the case, removed the Oscillator board and went through and tightened each individual contact in the connector. I couldn't figure out how to disassemble the connector like you suggested, but I was able to take a tiny screwdriver and push the individual contacts so taht they were tighter.

Thanks so much for the help! Sorry for "not getting it."

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