Mega Percussive Synth shell output VERY low

elmegil

My shell output (measured at J2, before the mixer) is only about .8Vpp to 1Vpp, so the level is extremely low. By comparison, the Impact output measured at that jack is about 5Vpp and the noise is nearly 15Vpp.

The mixer cuts the signals by half, and if I use the Line out, even at its maximum, that cuts it by half again.

I've replaced IC3 and IC5 with no change.

I've verified the various resistors in that section (e.g. R44, R24 & R25, R72) and the mixer (e.g. R77, R90).

On Scott Stites' site Thomas says: "The three resistors and one capacitor connected to pin 3 establish the proper output bias and amplitude of the triangle wave." Unfortunately I don't see where he says what that amplitude ought to be. I'm measuring a DC bias around 7V which is what I'd expect, and the wave itself is about 1Vpp.

In Locked mode, BTW, the shell output level (at the jack) is closer to 2Vpp, but that still seems WAY low. At pin 2 of the XR2206, it doesn't appear to change the 1Vpp.

I'm scratching my head over this, any suggestions?

elmegil · Posted: Mon Jun 10, 2013 7:36 pm Post subject:

So the discovery of the evening (so far) is that setting the ring mod balance seems to be affecting the level regardless of whether the ring mod depth is set to zero. The level is still significantly lower (it seems to me) than the other sounds, but it's much better with the balance set either all the way down, and best with the balance set all the way up. As in closer to 3Vpp better at J2.

Edit: And even so, when I plug it into my mixer (as opposed to my computer in jack) I still have to crank the gain so high that I'm listening to the noise floor if I want to hear any kick like sound from the shell. Even plugged into the shell out rather than the Synth or Line outs....

Edit 2: and re-re-re-reading Scott's site, I see "The output of each generator, jacks J2 through J4, is a nominal 10V peak-to-peak maximum."

So something is still messed up here, because I'm not seeing anything like that except the noise channel. :/

elmegil · Posted: Mon Jun 10, 2013 9:34 pm Post subject:

I just verified all my resistors and pots are correct; only one exception, the CV range pot R85 is 10k instead of 100k. Since I'm not trying to CV this yet, I don't see that being my problem (and the pot is one of a couple that are entirely surrounded by panel wires, so I will not be fixing it right away).

Can someone with a working MPS provide some voltages across the shell and impact circuits (sheets 2 & 3)? I just reviewed the official MPS thread and don't see any mention of Voltage or Level in this context.

ioannis taf · Joined: Sep 19, 2013 Posts: 5 Location: GREECE

Hello elmegil,
I have the exact same problem.Have you found a solution yet?
Thank you.

elmegil · Posted: Mon Sep 08, 2014 6:52 am Post subject:

Unfortunately, no. I've had many other projects on the slab, so this one has been sitting on the sidelines. Never got the voltage measurements either.

ioannis taf · Joined: Sep 19, 2013 Posts: 5 Location: GREECE

Built a second TH-MPS module and works just fine.Maybe, at some point, I'll get back to it.Thank you, though.

elmegil · Posted: Thu Oct 02, 2014 2:18 pm Post subject:

Ah, wish I had one good one and one bad one to compare the two Smile

ioannis taf · Joined: Sep 19, 2013 Posts: 5 Location: GREECE

Haha!Me, too!I donated the first one...But I believe, at some point, I will be seeing it again Wink