DOD 230 Noise Gate Switching

[RickL]

I was given one of these by someone who said it didn't work. It does seem to work but what I thought was the bypass seems to have no effect, it's always on. The spdt switch, wired as a spst, seems to just connect some component on the board (haven't checked which one yet since I have to remove the pot to look at the trace side of the board) to ground.

I looked at the MXR Noise Gate schematic in the schematics section and it looks like the bypass switch does the same thing. The DOD pedal uses an optoisolator unlike the MXR so it's not just a clone but I wonder if it "bypasses" the same way.

My questions are, particularly for someone who has one of these: is it a bypass switch?  or is a ground lift for the XLR? is it working correctly (what should I expect it to do)? One question really I guess 

[captntasty]

Have you taken any readings on the board?  Is it getting voltage?  I wonder if the switch hasn't been hacked?

[RickL]

The pedal does work. I haven't tested it with a noisey signal but with the threshold at about half way I get guitar signal through it which cuts off fairly abruptly as the signal dies down. Higher threshold settings let the signal last longer before it is cut off. Seems to work pretty much the same way any other noise gate I've used works.

The problem is that I get exactly the same results no matter what the position of the stomp switch. I've checked the switch and it is working. Other noise gates work as a gate in one position and pass all signals, no matter what their volume, in the other position. I think the reason the person who gave it to me thought it didn't work was because if the threshold is turned down no signal passes in either position of the stomp switch.

Some of the wiring doesn't look original but the unused terminal of the switch doesn't appear to ever have been soldered so my suspicion is that it was originally wired as a spst (supported by the MXR schematic that uses a spst). It might have been rewired but not drastically I think. Could the switch have been modded to effect only the XLR output? Or was it designed to be on all the time (makes a certain amount of sense for a noise gate) with the switch acting as a ground lift for either or both the 1/4" and XLR outputs?

[captntasty]

There are a few (very few) writeups on this one and all indicate that the switch is your garden variety bypass.  If the switch is set up as an spst it would seem to indicate that somebody has modded it for some other function, perhaps as you say, a ground lift.  I didn't find much info on this pedal.  Figuring out where the leads that run from the switch go to and being able to compare that to a schematic would tell you what's actually going on.

[RickL]

Update - I got it working. I'm still not certain exactly what the problem was, but I re-seated the input jack (ground contact via a star washer, no ground wire and it looked a little corroded) and worked the switch a whole bunch of times to try to clean the contacts. Now it "bypasses" fairly reliably. In one switch position the output signal is the same as the input regardless of the position of the threshold pot, in the other position a low enough threshold cuts off the signal, a higher position lets it through.

The switch is connected to ground (via the body of the XLR) on one end and to a 220k resistor, the collector of a 2N4124, the + lead of a 1uF electrolytic cap and pin 6 of a LM358N (- input of one of the dual op amps in the 358). The - lead of the cap goes to the emitter of the 2N4124. The other major components are a TL022 and a VTL5C2 plus a few caps and resistors. The output wire is connected to both the XLR and the 1/4" output jack.

If I had to guess I would say the switch works by defeating the gating action. Connecting the - input of the op amp forces it to be on (unity gain) all the time, removing the connection allows the gating circuit to work (turns the gain up only when the input signal is high enough). If the switch was dirty and not making proper contact the op amp wouldn't be forced on.

Just in case anyone was interested.