Help with AMZ Overdrive Pro (doesnt work when it's screwed together)

[adam_f]

Hey, this is my first go at building an fx box.
I've put together the AMZ Overdrive Pro from Torchy's layout:

http://www.indyguitarist.com/torchy/Distortion_Overdrive/AMZ%20Overdrive%20Pro/AMZ_OD_Pro.gif

And it works (except for a broken treble pot), but not when screwed together.

I built it in an old marshall footswitch box:



SO:

1. It works fine, except that there's a very low signal output when it is screwed together (the screws are connecting the top part of the box (mounting the switch and pots) to the bottom (mounting the jacks and DC plug).

2. Name of the circuit = AMZ Overdrive Pro

3. http://www.indyguitarist.com/torchy/Distortion_Overdrive/AMZ%20Overdrive%20Pro/AMZ_OD_Pro.gif for the layout and http://www.muzique.com/schem/projects.htm for the schematic.

4. No Modifications made

5. I substituded D1 and D2 for clear tint Red LEDs from Small Bear. IC1 is a JRC4558D. C5 was replaced with a 270pF cap.

6.Positive ground to negative ground conversion?  N

7.Out of circuit battery voltage? => 8.65 volts

Voltage at the circuit board end of the red battery lead = 8.62
Voltage at the circuit board end of the black battery lead = 0


Q1
C = 6.55
B = 0.85
E =0.29

Q2
C= 8.61
B= 1.57
E= 1.18

IC1
P1 4.28
P2 4.28
P3 3.87
P4 0
P5 0
P6 8.01
P7 8.01
P8 8.60

D1 (LED)
A = 0
K = 0.25

D2 (LED)
A = 0.20
K = 0

notes: I used a 3PDT switch and an LED for truebypass as on the tonepad offboard wiring pagehttp://www.tonepad.com/getFile.asp?id=76 (offboard wiring 5).

Clearly I can't measure the voltages when the box is closed!

Thanks a lot in advance. Any help will be much appreciated.

[dosmun]

Part of your circuit is most likely touching the case when it is put together,  or you may have a bad connection and the problem shows up when put in the case because of the way a wire is bent etc..

[Mark Hammer]

Pedals that work fine when on the bench and not when boxed together are very much like dogs that will do tricks for you but NEVER in front of strangers.

Common problems that arise when boxing up are:

1) Solder lugs get pulled by the wire leads and short out against each other
2) Screwing the retaining nuts on the pots from the outside rotates the pots a little bit and the pot lugs short out against the backs/lugs of other neighbouring pots
3) Twisting the pots and leads to fit them in place fractures one of the lead wires in a way that is hard to see
4) The exposed lead of a component on the board shorts out against back of a pot
5) The contacts on a phone jack (if a nonenclosed  one is used) touch something when a plug is inserted

Any one or all of these have happened to just about all of us.  What I like to do these days is to use heat shrink tubing around the lugs and end of the connecting wires to all pots and switches.  It insulates them from accidental contact, and also provides strain relief so they don't fracture quite as often.  A bit of a pain in the butt if you decide to change something, but less of a pain in the butt than troubleshooting.

[adam_f]

cheers for the response guys. Haven't found the problem as yet. I'm pretty sure it's not a faulty connection/fractured wire. I rewired all the internal wiring and it's still doing the same thing! As for connecting somethineg in the box, well it works when the box is pressed together, but as soon as the screw makes contact with the thread from the top half the sound goes. (it's still there just very very quiet). It gives me the impression it's something to do with the top half of the box connecting to ground? (it's a painted box, so will only make electrical contact when the screws go through). I scratched a little paint off where the sheild of the input and where the output jacks touch the box.

Any more ideas?! Are there any useful tests I could do with my voltmeter?

Thanks,
Adam

[Mark Hammer]

It's a bit like trying to see in the light in the fridge door goes off when you close the door, isn't it?

First place to start is to look at the height of everything, and potential points of contact, both underneath and on top.  Don't discount the battery as a potential short-causer either.  People glow about their true bypass switching, but I've had batteries short out against the solder lugs of a stompswitch because I didn't leave enough clearance inside.

[MartyMart]

I've used two of those exact boxes and they are quite "tight" inside !
Sounds like the circuit is grounding and pulling all your signal to ground.
Do this :

Stick some plastic ( like the cover on gtr string packs ) to the whole bottom plate inside
also the "top underneath" of the inside too.
I do this in every build, or I use 2mm thick "Play foam" from a craftshop cut to size.
This may prevent the component from grounding, and check that the jack sockets are not being
forced to "touch" the box walls when a jack is inserted (been there ! )

Marty.

[adam_f]

I lined the whole inside with duck tape, and hey presto it works like a charm! I think it was one of the caps touching the top. Thanks for all your help!

Adam