Troubleshooting silicon Tone Bender

[Subropontes]

I'm fairly new to building pedals and I'm learning a lot here.
I am having issues with this silicon Tone Bender and I'm struggling to figure out what's going on.
I get signal when the effect is bypassed but not when the effect is on, but I get some signal when I touch the back of the board which makes me think that is ground related. I have the board's ground wired to the input jack's ground, the jack's ground wired to the switch's ground and the battery's negative to the input's ring. I checked continuity and the board, jacks, pots and switches are all grounded. I double checked the connections and everything is fine, there are no bridges connecting strips and all the cutouts are doing their jobs.
What am I missing? What should I check next?








https://youtu.be/IJs0yqFdNp0

[GibsonGM]

Welcome to the forum!  Let's see if we can get you started troubleshooting this.

1) go here and check out the proper way to wire it all up, first, just to be sure you have it right.  There is a pdf file you can download and keep for reference, everyone should have this.

http://www.tonepad.com/project.asp?id=35

2)  If you get no results from the wiring check, provide the info asked for here and we'll try to help:  https://www.diystompboxes.com/smfforum/index.php?topic=29816.0


Usually the answer is found   Might take a little time, so hang in there.

[antonis]

Hi & Welcome, also..

>I have the board's ground wired to the input jack's ground, the jack's ground wired to the switch's ground and the battery's negative to the input's ring.<

What about output jack's ground..??

P.S.
As far as I can see, you use painted enclosure so be sure about out jack grounding by wiring its sleeve to any convinient ground point..

[GibsonGM]

^  Exactly this.  I wanted you to review your switch & jack wiring to make sure you are using the right grounding points. 

The risk of a ground loop from using a ground wire on the output jack is pretty minimal at such low voltage. If the jack ever comes loose, it's a horrendous racket, too!

[Subropontes]

Hi & Welcome, also..

>I have the board's ground wired to the input jack's ground, the jack's ground wired to the switch's ground and the battery's negative to the input's ring.<

What about output jack's ground..??

P.S.
As far as I can see, you use painted enclosure so be sure about out jack grounding by wiring its sleeve to any convinient ground point..

Thank you!
I do have the output jack grounded to the input's jack ground.

I changed the offboard wiring yesterday (still have the same issue) and I don't have the photo from before but this is what I had (this is the wiring I usually use) with the output jack's ground wired to the the input's ground:



And yesterday I changed to this one, which is the wiring the first post recommended and I decided to give it a go, just in case it was an offboard wiring issue:

[GibsonGM]

Ok, so you still get signal when bypassed?  If so, time for the debugging page I linked to in "2)" of my first reply to you! 

Eventually you'll need this no matter what, so here is something to build after you post the debug info back here.  http://diy-fever.com/misc/audio-probe/

[Subropontes]

Yes, as I mention in the first post it works when the effect is bypassed, it doesn't when the effect is on but I get a little bit of signal when I touch the back of the board.
I've built another one using the exact same layout and I had a similar problem, I get sound but only if I play the low E and it's super farted like it's really underbiased but if I touch the back of the board I get signal with fuzz and it reacts normally to the knobs and it sounds decent.
Can both be just a bias issue? Why would it works differently if I touch the back of the board?
Both of them have basically the same voltage, here's what I got:


The one with farted low E that works semi normal if I touch the back:
Q1 C 6.7, B 1.4, E 0.49
Q2 C 1.52, B 0.62, E 0.5
Q3 C 4.22, B 1.53, E 0.92
Video:

https://youtube.com/shorts/4NwIIA4nOHE?feature=share

The one that has no signal and it gets some signal if I touch the back:
Q1 C 6.59, B 1.5, E 0.50
Q2 C 1.53, B 0.63, E 0.4
Q3 C 4.03, B 1.52, E 0.92
Video:
https://youtube.com/shorts/IJs0yqFdNp0?feature=share

[antonis]

100nF greenie cap hides the existence(?) of 1N914 diode..

In case of it is there, try to short it (solder a small piece of wire on its legs) and see what happens..

[aleks_tedstone]

Have you tried to adjust the trimpot through its full range? I know this seems like an obvious question especially as you have mentioned transistor bias yourself, but if you have some signal then this might be the key to at least fixing the one you describe as working 'semi-normally'. In the video clip it does indeed sound very gated, it might be that your finger can provide enough conductivity to properly bias the transistors.

The other one seems to work well as a radio, so its clearly amplifying something... This may need more extensive debugging as per GibsonGMs suggestions.

As you have socketed the transistors you could pop them out, measure the hfe and check that it is appropriate for each position, as this a lot of other forum threads discuss, the circuit can be quite sensitive to the actual values of these components, and how you bias them, and their leakage. 

[antonis]

The other one seems to work well as a radio, so its clearly amplifying something...

Actually, it rectifies something prior to amplification..

[Subropontes]

100nF greenie cap hides the existence(?) of 1N914 diode..

In case of it is there, try to short it (solder a small piece of wire on its legs) and see what happens..

Thank you!
I'm not sure if I know what you mean. Could you explain it?

[Subropontes]

Have you tried to adjust the trimpot through its full range? I know this seems like an obvious question especially as you have mentioned transistor bias yourself, but if you have some signal then this might be the key to at least fixing the one you describe as working 'semi-normally'. In the video clip it does indeed sound very gated, it might be that your finger can provide enough conductivity to properly bias the transistors.

The other one seems to work well as a radio, so its clearly amplifying something... This may need more extensive debugging as per GibsonGMs suggestions.

As you have socketed the transistors you could pop them out, measure the hfe and check that it is appropriate for each position, as this a lot of other forum threads discuss, the circuit can be quite sensitive to the actual values of these components, and how you bias them, and their leakage.

Yes, I did. If I have the trimpot all the way up is when I get that gated sound coming through, anything less than that I get no signal which makes me think that is a bias thing but the voltages I'm getting on both don't sound too far off (as far as I'm aware with my basic knowledge) so I don't know.
I only socketed the transistors on the one that I have no signal at all. I have 3904 on Q1 and Q2 and a 5088 on Q3 for both. I tried all 3904 and all 2222a and still had no signal. I didn't try all 5088 so I'll give that a go because why not.

[antonis]

I'm not sure if I know what you mean. Could you explain it?

This..

[GibsonGM]

I'd try antonis's suggestion, it is a quick test.   If that does nothing, I'd then use my audio probe to see where the signal degrades (after removing that jumper).

While playing a note, Audio Probe Collector of Q1...base and collector of Q2.  Somewhere in there the signal should go from 'normal' sounding to crap, that may tell something.  Voltage at Q3 collector is 4.03, close to the nominal 4.5V, so bias could make it SOUND a little off, but it seems that it should WORK at this point, barring a bad connection or bad part, etc.  Even better, try to dial that to 4.5 with the pot before probing, if you can.   Don't short out anything while you probe

There could be a solder bridge or cold solder joint making a bad contact, for one thing. Since you do have signal at output, it's probably nothing huge, just that you have to find it!

[Subropontes]

Thank you for all the tips! I'll check for cold solders and reflow everything that looks dodgy, if that doesn't work I'll try Antonis' suggestion and if that doesn't work I'll put them in a drawer and move to other projects to get some sort of gratification before going back to troubleshooting these. Haha