Spike problem with Moog Prodigy

[ribnib]

Hi!

I have a thumping or spike problem with my Moog Prodigy. It seems to be affected by Attack and Decay/Release. I can cindof move the "thump on" with attack time. The "thump off" only appears when the key is released prior to the tone decaying out with the decay time.

I adjusted the VCA balance trim, which on mine is R120, and did gain a little more signal to spike ratio. But it is quite menacing leading me to think there is something wrong. I don't have sufficient knowledge to start testing in there, but I thought I'd put it out here and see if any of you have a suggestion. Im thinking its something to do with capacitor c44 which plays a role in the whole ADSR thing. ( i think thats c40 on the prior 4160 models)

Also there is quite a bit of noise when osc. are turned down and only thump is heard. If I hold the "note" it hisses.

Any thoughts would be much appreciated!

[meatballfulton]

Some amount of clicking on envelopes is normal on analogs with fast EGs. Some people even like it as they think it makes the sound punchier

You're on the right track with the VCA balance trimmer. It should go through a null where the clicking is at a minimum. If instead you're reaching the end of the trimmer before you hit the null there could be a problem somewhere else.

As far as hiss with all oscillators off, hey it's analog I'd check the signals coming out of the mixer and see if the hiss is as apparent there.

[Esus]

There is a similar thread on the Moog forum (might even be you)...

http://www.moogmusic.com/forum/viewtopic.php?t=7860

Kevin L has some good info.

[ribnib]

well.. "ribnib" that is me on the moog forum.

this clicking or thumping is a lot louder than oscillator signal even at the best VCA trim point. And the hiss i talk about is only when a key is beeing held, after the thump/click, as if there was a noise generator beeing activated.
I am not talking about the noise floor of the unit.

thanks for helping

[ribnib]

Does anyone know if a voltage difference on the power supply could be causing this thump? I'm measuring 11,9 negative and 11,6 positive voltage over the capacitors c39(-) and c38(+) to ground. The audio output is registering a spike of around 0,2 volts. Is this purely coincidence?

[on-the-run]

SOLVED: the keyboard connector was connected upside down.