Help Debugging Tone Bender Professional Mk II

[littlegreiger]

Hi everyone, haven't been around for a while, kind of put of building pedals to work on some other stuff. Anyways, I came back to build some projects that I had ordered parts for a while ago.

I put together the Tone Bender Professional MK II using a vero layout I found in the gallery section and needless to say it didn't work as planned.

Here's some info on my build

1. What does it sound like?
Here's the weird part, when I first built the circuit a couple weeks ago (took some time off after it didn't work) when I first hooked it up the circuit worked for about 5 seconds and then stopped. It was kind of like a cap was discharging really slowly. Today when I hooked it up to my Danelectro battery powered amp it did this again but after I switched the pedal on and off again it worked great. So I tried it with my Fender 15 w solid state combo and all it did was amplify the sound and add a lot of noise to it.

2. Circuit Name:
Tone Bender Professional MK II

3. Source of Circuit
DIY Stompboxes Gallery

4. Modifications
None

5.Subsitutions?
None

6. Positive ground conversion
No

7. Voltages
Battery: 7.98
Red Lead on board:7.96 (started at 7.2 and rose slowly for a couple minutes)
Black Lead on board:0.00

Q1
C:7.9
B:7.84
E:7.96

Q2
C:7.38
B:7.85
E:7.96

Q3
C:4.41
B:7.38
E:7.5

C2 (input electrolytic cap)
+ve:1.71
-ve:7.85

I know that the voltages on C2 don't look right, but I'm not sure how there could be much voltage on the positive side seeing as it's only being driven by a guitar output.

Other Notes: Using set (3) of matched Ge Transistors from Small Bear.

My first thoughts are it's either misbiased (most problems found on the board) or one of the caps is bad (weird voltage fluctuation and weird sound at beginning).

Any help is appreciated and I'm going to see if I can dig up some replacement caps in case that's the problem.

[Schappy]

All your transistor voltages are pretty much incorrect.

You shouldnt be getting that high of voltage on the base and emitter of your transisitors.

The base must be higher than the emitter.
You are getting way to much voltage to the emitter and base.
Maybe a solder bridge or improperly made cut in the vero?

Check this site to compare voltages.
http://www.home-wrecker.com/tbmk2.html

1) Double check your layout and make sure everything is correct and all cuts are made properly.
2) Check pinout on transistors
3) Build and audio probe and probe through the circuit to find the problem.

[littlegreiger]

Thanks for the ideas and the link to that site. I knew the voltages were wrong but posted them anyways in case some one might have seen something they experienced before.

I checked the pinouts and they're all correct, I've also checked the board and everything is placed and there's no solder bridges and the cuts are made cleanly.
I'll audio probe it tomorrow when I have the time, but last time I did (when it was first built) the signal starts to screw up around Q3.

[R.G.]

This is an inherently positive ground pedal. Did you check to see that the battery/power leads are correctly hooked up?

You should have the red battery wire going to signal ground and the black wire making -(battery voltage).

Also, a battery under 8V is on its last legs. That may mess up some things all by itself.

[littlegreiger]

I think I have the leads hooked up correctly. I have the red lead going to the +9V on the board and the black lead going to the ring on the input jack. Thinking about it now I don't think that's right. Also I'm gonna grab a newer battery next time I test it, that was just the first one I grabbed from my shelf.

EDIT: I checked out the layouts for positive ground pedals and I'm pretty sure I messed that up in mine, I guess I didn't really think about it at the time. I'm going to rewire it tomorrow and see how it goes.

[petemoore]

  Q1 and Q2 emitter [and everything else shown there on schematic] are common to the positive Gnd. [..+red battery clip lead]

[littlegreiger]

Yeah, I think I may have screwed up the grounding as this is my first positive ground pedal.
Also when I'm taking voltage measurements should I have the black probe on the red lead (+9V)?
Thanks

[Schappy]

It really doesnt matter.

You will get a negative reading if it is switched.

[littlegreiger]

I rewired the off board wiring and that was it, I had the grounding system wired essentially like a negative ground pedal  . Guess I know for next time.
Thanks for everyone's help and hopefully I'll be around here more often.