Wem Pepbox germanium build problems. Can you help?

[Boxcarwillie]

Hello everyone!

I'm trying to build a wem pep box type pedal with germanium transistors (pnp) which requires a +ve ground circuit.

I've built it according to this circuit diagram:

https://4.bp.blogspot.com/-tbrvn34Bgsw/VdzL-59yEhI/AAAAAAAAF3E/W12fKenBDz8/s1600/WEM%2BPep%2BBox%2B-%2BGermanium.png

Wired the 3PDT footswitch like this:

http://www.tdpri.com/attachments/forumrunner_20121229_091235-jpg.158546/

Wired the tips of the jacks to 'in' and 'out' as per the diagram, then wired the sleeve of the jacks to the ground of the circuit.

I'm sure some of you will laugh but... built the first prototype 'off-board' so to speak! Here's a picture if it helps


I built the second prototype on a perf board, but after having the same result, I amended it to resemble this circuit:

https://www.diystompboxes.com/smfforum/index.php?topic=95765.0

Still no joy. Here's a picture of the second build attempt:



Basically what happens is that you get true bypass whether the circuit is connected to power or not, when you power and switch to the circuit you get a quiet sound of the guitar signal that is totally unaffected by adjusting the pots, and a loud buzzing noise.

I am powering the circuit from a Walrus Audio Phoenix power supply using a reverse polarity cable.

I have tested the transistors with a multimeter - I don't know if there is more advanced testing that can be done? They are NOS from eastern europe. I used different ones on the second build in case the first two happened to be bad.

A lot of head scratching done around the +ve ground issue and whether or not things are connected the right way round, but I tried switching things - for example the direction of the first capacitor is different in the two circuits, so tried that in both directions - no change there.

I used a 50k pot instead of a 500k with a 56k resistor - which is apparently the original configuration - but surely that wouldn't be the problem?

I'm a bit baffled at the moment. Any help would be hugely welcome and appreciated. Thank you!

[GibsonGM]

I always try a circuit out before adding the 3PDT and jack ground switching.   VERY helpful to know it works before you complicate it with switching.  It could be worth your time to remove it and hook things up with jumpers...

Can you power it from a battery? (remember, watch that positive ground!)  that can remove a little complication.

"Loud buzzing" suggests a ground problem...it can also mean "dc is being passed", which happens when a cap is missing or totally shorted, or by some other thing (short) that allows DC to mix with your audio unchecked (and bzzz would be ripple from a wall wart, not a battery.  Crackle when moving pots is another give-away of DC present).   Bad ground is more often the culprit tho, so check that all grounds are connected.  Usually, there is a wiring error - esp. if you say the pots do nothing. So, all you can do is...go over it all again!   You'll figure it out, or will find other symptoms to report back.

I wouldn't think the 50k vol pot would make a huge difference...a bit quieter maybe, but not "non functioning" as you report; worry about that later.

[Boxcarwillie]

Thanks GibsonGM, good thoughts.

I have gone through the circuit multiple times and everything seems like it is wired correctly.

I mention the jack and the switch in case there was something odd there that had shorted the circuit or something.

I did actually remove the switch at one point and that didn't seem to make any difference.

The jacks seemed to need to have their 'shields' grounded to the circuit otherwise they created a huge buzz. Am I missing something?

[thermionix]

I always try a circuit out before adding the 3PDT

I think it needs to be in giant letters at the top of the forum.

[duck_arse]

welcome to the forum, Boxcarwillie. I expect to see this pic posted in the "wood finish pedals" thread. we love odd build methods around here.



check that your jack socket grounds are actually where you think they are. meter for resistance from board ground to the jack sleeve/mounting threaded thing to check you aren't sending signal to ground. also, voltages, measure and post, please.

[Boxcarwillie]

Hey Duck Arse, thanks for the advice!

Just thought I'd add it's a positive ground circuit if that makes a different. I'll get some readings up as soon as I can.

[Boxcarwillie]

Hi Duck_arse

So measuring from jack sleeves to circuit ground gives a zero voltage and no resistance reading.

Question. With it being a positive ground circuit, just to confirm that you connect the tip of the jack socket to the input/output of the audio circuit.

[Boxcarwillie]

What do you connect the ground of the jacks (sleeve) to if the ground of the circuit is positive??

Taken out the switch, and when there is no power connected to the circuit, and I connect the jack grounds together, I basically get a bypass. Does this make any sense???

[duck_arse]

for our purposes, the sleeves are always ground, the signal always appears on the tips. doesn't matter to the outside world whether it's a pos ground or neg ground, as long as it's wired right.

so, when measuring voltages, black lead always goes to ground, ground is always the jack sleeves. red probe then pokes at circuit nodes, and if neg ground circuit will return positive readings, and if pos ground will return negative readings [single supply circuits only, obvs.]. if the meter indicates a negative reading, you need to include the sign in your posted voltages so we know what's waht.

again so, if your circuit is pos grnd, connect sleeves [ground] to the supply + [red, whatever], call it all ground and do black probe measure from there. it will become easier after you've used it a few times - or just completely avoid pos grnd builds.

when you do resistance measures, you disconnect the supply volts, otherwise it will mess with your readings. I was wanting to know that you had ground from sleeve in-circuit ground-sleeve out to rule out a miswired jack tip.

and if you are using a sleeve & ring jack power switching arraignment, you are still connecting sleeve to ground when the ring is shorted by an inserted plug [so the ring also become ground].