Stage Center Reverb problems

[mth5044]

Finally finished wiring up my stage center reverb, but it has some... issues.

Luckily, I'm getting sound. The sound is muffled, reverby nonsense, plus it is less then half the volume of when it's off. I tried some of the mods (probably foolishly) before I built the circuit stock. Here is the layout I made from the mods suggested by Mark Hammer.



with a few changes.

I didn't add in the pre tank loop, I didn't add in post tank loop, instead of doing the switch with the capacitors in like the way I drew it out, I used a SPDT on/off/on switch, putting the 12nF cap in the middle, also attached to the send side of the wire, then another 12nF on one side, and a 39nF on the other, which I think is basically the same thing.

Finally, when wiring it up, I moved the center lug of the mix pot:

http://www.generalguitargadgets.com/pdf/ggg_sc_reverb_lo3.pdf

down to the pad up from C2 so it would make the connection. If it was left where it was supposed to be, it wouldnt connect to anything. Make sense? I hope so. I'm trying to think of things to check, but I'm not coming up with anything.

[mth5044]

I've been giving it some thought, and I'm thinking the reason that the output is so.. bad is because the signal isn't being boosted enough or being regained enough.. maybe.

I also won't have my multimeter until later today, but I need to also check that the power pump is working, getting +9 and -9 volts out of it..

hmmm.

Two of the controls are acting as volume controls, and two aren't doing anything, I forget what ones do which but I will find out this afternoon.

Stay tuned in for more exciting adventures.

[mth5044]

Alright, so everything is good with the charge pump. It is putting out it's + and - 9 v's.

A problem I found was I had the 10k and 500k pots switched up (made the enclosure a while ago and misslabeled the pots)   

That didn't fix much, but I am locating the source of the problem. The mix pot is doing something a bit strange. From off to full, it starts out dead quite, then slowly brings in the dry signal, which sounds good (maybe a little treble loss, but nothing significant), then once the dry signal gets to unity gain with the bypass, it starts to mix in the wet signal.

The wet signal is what is distorted and, frankly, would sound fantastic if I wanted a distorted reverb, but nothing clean.

So my only thoughts now are to replace the diodes or the tl074, unless someone could provide some insight or some voltages to see if any of them are the problem. This thing is a monster.

[mth5044]

Bump for the monday crew 

[petemoore]

  IIRC the SCR's opamps are all gain stages ?
  Look for typical bias, the schematic is much easier to read:
  http://www.generalguitargadgets.com/diagrams/stage_center_reverb_sc.gif
  It is an input buffer and a batch of amplification stages.
  'F' should have a strong signal, enough to drive a transducer.
  'E' should likewise provide a boost from the recovery to output circuit.
  Taking pin voltage measurements is always informative.