Help with true bypass on wah

[kevn]

I just finished wiring my dunlop GCB-95 wah for true bypass using a DPDT switch. The wah side of the switch seems to work fine, but the bypass side cuts off the signal to the amp. There were a couple of assumptions I made in the wiring, one was that the orientation of the switch didnt matter, that is, if I had the switch oriented one way, that I could turn it 180 degrees and still follow the wiring diagram. The other was that the wire going to ground could be fastened to the screw holding the circuit board in place as this would attach it to the casing which is the correct ground point. I'm guessing that the ground wire is the problem & that I need to connect it elsewhere. Any thoughts?

Thanks,
Kevin

[niftydog]

One thing I can say for sure, if you intend to continue DIYing, you absolutely need to get a multimeter! Why? Because a multimeter will be able to tell you definitively if there is an electrical connection to ground via that screw. It will also allow you to check the operation of the switch to make sure you have it wired correctly.

Most switches are symetrical along one axis only. So, your assumption is correct, but I have seen people wire them incorrectly because they were 90 degrees rotated from where they should be. however, that's usually only a problem with 3PDT. Take it a step at a time and work back through that diagram checking your work.

Anywho... I don't think the ground wire is the issue, I think it's your wiring. What diagram did you follow?

[petemoore]

 Â Ground's probly find if the circuit sounds good. You can check all grounds shown in the schematic on your circuit board and offboard, using the DMM.
 I guess you may have a bypass wire connecting the two throws on one side of the switch, the circuit In and output wired to the poles [should be to the other separate throws], and the jacks wired to the other side of the byapss wire, to the other throws. The jacks need to connect to the 'middle' lugs, An input jack wire assigned to a throw that goes to the bypass wire *or input to circuit, and an output jack wire assigned to a throw that goes to the other side of the bypass wire *or to circuit output...depending on *switch position.
 Like this
 with switch lugs facing you, two columns of three lugs.
 Lug 1 and 4, bypass wire goes across these.
 Lug 2 input jack tip
 Lug 3 Input to circuit
 ....
 Lug 5 [will be adjacent from lug 2] output jack tip
 Lug 6 circuit output

[kevn]

 
Well, I have a DMM & the ground is electrically connected to the chasis via the screw.....

I followed the instructions on this site for the Rev E Board:

http://members01.chello.se/pastorn/fx/mods/dunlop.htm

Heres a mapping of what I did to the above description:

  Lug 1 and 4, bypass wire goes across these. (Check, assuming 1 is top left & 4 is bottom right)
  Lug 2 input jack tip        (Check)
  Lug 3 Input to circuit       (xxxxxGroundxxxxx)
  ....
  Lug 5 [will be adjacent from lug 2] output jack tip  (Check)
  Lug 6 circuit output  (Check)

[niftydog]

I think there's some confusion with the numbering here.



Following the above diagram (looking at the bottom of the switch)

1 and 4 should be wired together.

2 should be the input jack

5 should be the output jack

3 should be the circuits input

6 should be the circuits output

Lug 3 Input to circuit       (xxxxxGroundxxxxx)

What do you mean by this, it looks bad!

[kevn]

If you look at the instructions from the web page in my 1st post it has:

1 & 6 - tied together
2       - "New wire to effect input"
3       - "Connect to ground"
4       - "Blue wire from pot = effect output"
5       - "Purple wire from harness = output"
6       - "Green wire from harness = input"

This wiring is specific to post 90 Rev E,F & G boards modified as described in the document. Reading through the instructions more carefully (as opposed to just following the diagram) I noticed two notes specific to the Rev E board (90-91), which is what I have. That is the green wire from the harness goes to lug 2 and the new wire goes to lug 6.

The new wire is soldered to the tip of a pad connecting it to the tip of the input jack, where the trace connecting this jack to one of the pin connectors has been severed. I'll have a chance to switch the two wires some time over the weekend & will let you know how it goes.

Sorry about the mix up, I shouldnt be in such a hurry as in the long run I would have saved myself & anyone else who has helped here some time by reading the instructions more carefully!

[powerplayj]

Both should be correct in respect to switching between the pcb or bypassing it.  Kevn's diagram just grounds the switch.

I am working on my wah as well and was wandering if the switch needs to be grounded via a lead to the board or a jack sleeve? 

Kevn,

assuming your wah worked before, I would think that the ground you speak of might be the problem.  Seems like when I had my stock wah circuit in, I just grounded the switch to the back of the pot.

[kevn]

Well, I just switched the wires as described in my last post & everything worked as advertised. I left the ground as is, which, with chords plugged in connects the chasis to the ground lead on the board.

Unfortunately I now have another problem. I was playing through it, both on and off, also comparing bypass mode to patching directly into the amp and everything was perfect. I noticed that the switch was up a bit too high so I adjusted the height so that I had to press into the rubber to engage it. Hooked everything back up, hit a chord, pressed it down to wah, and, squeeeel. A high pitched noise started coming through, kinda like feedback. On this one I'm completely at a loss & have no idea what to check. I wonder if I might have damaged the switch with that extra bit of desoldering & soldering to switch the wires (terminal 6 was a bit loose). Anyone suggestions on how to dignose this one would be greatly appreciated!

[niftydog]

you sure you didn't short out the bottom of the switch on something? Does the squeal go away or is it constant now?

[kevn]

Well, I took my meter & tried to find something out of place, but found nothing. So I put it back together and tried it again and now everythibg is fine. I dont know what was causing the squeeling noise but hopefully I wont recreate the condition any time soon. So now onto more tweaks to this wah. I'm going to try different transistors & am waiting for a red fassel to arrive. I'm going to wire the inductor with a switch so that I can have 2 in place.

[kevn]

Niftydog, I was putting in my update as you were responding. As I mentioned above, the squeel went away & I cant make it happen again. I would like to know what caused it, but thats out of reach unless it happens again. When it did happen it was a constant squeel w/o any guitar tone coming through.It would also wah a bit if I moved the pedal back & forth.

[niftydog]

ah... are you sure you didn't hook up the cables backwards? Wahs are known to create some pretty hoopy sounds when you do that and that's ringing a bell now when you said "It would also wah a bit if I moved the pedal back & forth."

[kevn]

Thats possible, although I tried that to see if it would cause the squeel (having read someone elses post on this here) & it didnt (although I may have had my SD1 in the path originally as well). Anyway if thats what caused it I'm not too concerned. I'm more worried about it being a bad connection in the circuit which doesnt appear to be the case.

[jimlam]

Could be a case of imcomplete switching on the part of the switch.

For my own wah, I like it to be a bit higher so that I dont have to stomp on it that hard to switch it off. Its hard to concentrate on putting so much effort to switch the wah off while playing and if its too low, it may not switch on/off reliably and you may get that screech noise. When the switch was too low on mine, it would sometimes squeel because it was like in an inbetween position(I think thats what happened). When I adjusted it up so as to make it easier to switch on or off, it seldom occurs.

BTW, where do you find space on the board of the gcb95 to have two inductors? I'm also planning to have a red and yellow fasel in there and cant quite decide yet how best to fit it in the small space.

[kevn]

I was actually thinking of finding space off the board to place the inductors & running wires to a switch and to the board. Where & how I havnt decided yet. In preparation I took my stock inductor off last night, mounted connector pins, soldered wires to the inductor and temporarily hooked it up taping the inductor to the side of the chasis & isolating it with some thin cardboard. This seems to have reduced my pedal to sort of a volume pedal w/o any wah. I need to check that proper connections are being made & nothings shorted which I didnt have time to do last night. I will say though that I was getting some cool sounding volume swells, especially on the low E string.