new member and a debugging question

[charriman]

Hi guys,
I just completed my first kit build.  Its a GGG TB2 silicon MKII Tonebender.
The good part is that i'm hearing fuzz when i first fire it up.  The problem is there is hardly any output with both the volume and attack knobs wide open.  I had to turn my amp up to about 5 to hear it.
do you guys have any suggestions on where to start
Here's the layout if anyone needs it.  I did do the trimpot in place of R6 if that makes any difference.  I assume the trim is for the bias of Q3.
Thanks in advance.
Chad

[charriman]

one more thing.  I adjusted the trimpot and did get more volume up to a point.  Counterclockwise gave me the volume jump and clockwise dropped the volume but started gating.  It seems as if the volume pot does nothing at all.  Possible volume pot issue?  Bypass signal works fine.

[LucifersTrip]

posting the schematic, any changes you made and most importantly the transistor voltages is the best way to get the best help

[charriman]

Here's te schematic. The only change was the optional trimpot for R6.
http://www.generalguitargadgets.com/pdf/ggg_tb_m2p_sc_ns.pdf

How does one go about checking the measurements of the trannies?
Pardon my newbieness:-)

[chromesphere]

Hi Charriman,

As you are new to building guitar pedals, i'll just throw a few things at you that i usually do when i have a pedal thats not behaving properly (usually means i've made a mistake, happens to the best of us).

- Check the traces for solder bridges
- Check the values of the components
- Check the orientation of the components

Thats usually where i start.  You could also consider posting photos of both sides of the boards if you need someone to check it over for you.

Good luck
Paul

[LucifersTrip]

- Check the traces for solder bridges
- Check the values of the components
- Check the orientation of the components

the voltages will many times pinpoint all of the above. that's why it's #1

[LucifersTrip]

Here's te schematic. The only change was the optional trimpot for R6.
http://www.generalguitargadgets.com/pdf/ggg_tb_m2p_sc_ns.pdf

How does one go about checking the measurements of the trannies?
Pardon my newbieness:-)

it's in the link I gave above:

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1
C =
B =
E =

Q2
C=
B=
E=

[charriman]

Here's te schematic. The only change was the optional trimpot for R6.
http://www.generalguitargadgets.com/pdf/ggg_tb_m2p_sc_ns.pdf

How does one go about checking the measurements of the trannies?
Pardon my newbieness:-)

it's in the link I gave above:

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1
C =
B =
E =

Q2
C=
B=
E=

Awesome LT.  Thanks!  i didnt realize the "click Here" %^&*roach was a link.. Sorry.
I'll get those numbers for you.

[charriman]

OK.. LucifersTrip... got the voltages.
Here's the completed checklist:
1:  LED lights up, Attack control works, i can hear Fuzz faintly in the background but i have to crank the amp to get any sound.  Passes clean signal when bypassed.  Volume knob appears to do nothing.  It did however get a tiny bit louder by adjusting the trimpot for Q3.

2: General Guitar Gadgers Silicon Tonebender MKII
3: http://www.generalguitargadgets.com/pdf/ggg_tb_m2p_sc_ns.pdf
4: No modifications made to the circuit
5: R6 substituted for the included trimpot.
6: No
7: Battery voltage out of circuit: 9.1
    Battery voltage @ circuit board end of circuit: 9.03
    Voltage @ board end of black battery lead: 0.  Black battery lead is grounded to input jack. The board's power supply ground is connected to the power adapter jack.

8:  Voltages on transistors:

Q1
C=6.72
B=0
E=0.57

Q2
C=1.35
B=0.51
E=0.1

Q3
C=5.4
B=1.35
E=0.76

There are no ICs or diodes/zeners in the circuit.


Thanks for the help!  Take note of the pic above and excuse the abundance of excess wiring 

[LucifersTrip]

first look for problems around Q1. It is impossible that the Q1B voltage = 0

[charriman]

first look for problems around Q1. It is impossible that the Q1B voltage = 0

I was pretty sure that was not right, but having absolutely no electronics knowledge, i wasn't exactly sure.  I'll reflow the solder on the socket for Q1 and try it again.
Thanks... I'll let you know.

[charriman]

Ok.. I think i was screwed up with my measurements.  I pulled Q1 out of the socket and re-soldered the pin for the base.  Tidyed up a couple of other things.  Now i'm getting no sound, only bypassed.
Here are the measurements for the trannies this time. (i think i neglected to put the - sign in the last time.

Q1
C=6.72
B=1.07
E=0.56

Q2
C=1.35
B=0.51
E=0.01

Q3
C=5.32
B=1.35
E=0.76

also, here's a pic of the back of the board.

[LucifersTrip]

Here are the measurements for the trannies this time. (

Q1
C=6.72
B=1.07
E=0.56

Q2
C=1.35
B=0.51
E=0.01

Q3
C=5.32
B=1.35
E=0.76

the next step is to check your voltages compared to others that work...it's time to do searches on this and the other forum and google.

I found this right off, but didn't read thru it.
http://www.diystompboxes.com/smfforum/index.php?topic=71849.0

Q1 (hfe 69)
C 7.76
B 1.00
E 0.41

Q2 (hfe 110)
C 1.87
B 0.63
E 0.00

Q3 (hfe 217)
C 3.07
B 1.87
E 1.23

Yours are closer to what they should be (a ge tonebender Q3C should be ~7-8.5v...not sure about the si one but you're way better with 5v than he is with 3v)...yet, he's getting an OK tone and you have nothing....which leads me to believe that your offboard wiring is off. make sure the switch and jack are hooked up correctly.

note: this whole thing should've been breadboarded first so you wouldn't have to guess if it's the circuit or the offboard part.

but in this case, since your voltages aren't bad, it's prob offboard

[Jdansti]

Your solder job on the board looks nice and neat.

Double check the 3PDT bypass switch for proper wiring and that there are no stray strands of wire touching adjacent terminals.  Cut off any extra wire hanging outside of the solder on the lugs.  The photo's a little out of focus for me to tell if it is wired properly.

Also check that you have a good ground connection between the in and out jacks. I can't tell if you're using the box for one of your ground connections, but if you are, it could potentially cause a bad ground path. 

[charriman]

Your solder job on the board looks nice and neat.

Double check the 3PDT bypass switch for proper wiring and that there are no stray strands of wire touching adjacent terminals.  Cut off any extra wire hanging outside of the solder on the lugs.  The photo's a little out of focus for me to tell if it is wired properly.

Also check that you have a good ground connection between the in and out jacks. I can't tell if you're using the box for one of your ground connections, but if you are, it could potentially cause a bad ground path. 

Would that still be in play if i'm getting signal passed in bypass mode?

[LucifersTrip]

Your solder job on the board looks nice and neat.

Double check the 3PDT bypass switch for proper wiring and that there are no stray strands of wire touching adjacent terminals.  Cut off any extra wire hanging outside of the solder on the lugs.  The photo's a little out of focus for me to tell if it is wired properly.

Also check that you have a good ground connection between the in and out jacks. I can't tell if you're using the box for one of your ground connections, but if you are, it could potentially cause a bad ground path.  

Would that still be in play if i'm getting signal passed in bypass mode?

he reiterated what I said...check the jacks & switch....

not as probable for the jacks, but yes, you could get nothing when the effect is engaged if the switch isn't wired properly

best thing to do is try it wired straight thru with no switch, to remove that from the equation

[charriman]

I got it.  You guys were right. I pulled a dumbass
Move and forgot the wire between the switch and lug 2 of the volume pot.
Well that and giving me that checklist that helped me find that bad solder joint on the tranny.
Thanks for all the help!

[Jdansti]

Aha!  The ol' no output wire causing no output mistake!   

Glad you got it going!