Debugging fuzz pedal

[andershp]

Hello

I've built a "clone" of a VOX Tonebender using this circuit drawing:



and this true-bypass setup/how to:



I've built it on veroboard and it's my first build using that.

The bypass and the LED works fine, but there is no sound at all when the pedal is activated - how do I debug this?

I suppose the problem is on the circuit board, but how do one find the specific place or component?

Thanks

[Greenhill]

Voltages on Q1 and Q2 ?

[EATyourGuitar]

you can also check all your solder connections for continuity at the leg of each component. it could be a mistake on the vero layout or transistors are backwards. could be a lot of things but you get closer by process of elimination. posting the voltage for everything on here lets us help you.

[stringsthings]

Hello ....

... how do I debug this? ...

.... how do one find the specific place or component?

Thanks

hello ! .... debugging a build is a process that all DIY'ers must eventually come to grips with ... i would first recommend that you purchase a DMM ( digital multi-meter ) ... this tool will soon become your best friend when it comes to debugging circuits ...

[LucifersTrip]

 

[andershp]

hello ! .... debugging a build is a process that all DIY'ers must eventually come to grips with ... i would first recommend that you purchase a DMM ( digital multi-meter ) ... this tool will soon become your best friend when it comes to debugging circuits ...

Yes, that is why I ask here - to learn how to debug these things and I do have a DMM.

Voltages on Q1 and Q2 Smiley ?

Q1
C = 0.14 V
B = 0.10 V
E = 0.00 V

Q2
C = 7.38 V
B = 0.14 V
E = 0.10 V

I haven't done this kind of debugging before so sorry if things are obvious, however I think that these values seems a little weird...

I have done some testing of the soldering and it seemed allright, but I may need to do it again - I just thought that somebody maybe can see the problem from the Q values.. I will post more if needed, but again I haven't done any debugging before and I have only done one build before as well.

[Govmnt_Lacky]

Q1 Collector/Q2 Base are wrong. Should be higher.

Q2 Collector should be biased around 1/2 of the V+ input.

Check to make sure you didn't mix up the 1K and 10K resistors off of Q1 and Q2's collectors.

Good Luck 

[andershp]

Q1 Collector/Q2 Base are wrong. Should be higher.

Q2 Collector should be biased around 1/2 of the V+ input.

Check to make sure you didn't mix up the 1K and 10K resistors off of Q1 and Q2's collectors.

Good Luck 

I don't know what you mean by "Q1 Collector should be biased around 1/2 of the V+ input" (sorry I'm danish so some of these technical words are a bit strange to me), but I guess it means that the voltage of the Q2 C should be half the 9V input voltage?

The color codes of the 1K and 10K resistors are right but I haven't tested them, but can they possibly make the whole pedal silent? Can I test it somehow or do you have to replace the resistors to find out if they were the problem?

[Govmnt_Lacky]

I don't know what you mean by "Q1 Collector should be biased around 1/2 of the V+ input" (sorry I'm danish so some of these technical words are a bit strange to me), but I guess it means that the voltage of the Q2 C should be half the 9V input voltage?

Yes. Your Q2 collector should be set to half of your input voltage. If you are using a wall plug, this may be higher than 9V. You need to use your DM and measure your input voltage then make sure you have half of that on the Collector of Q2. If not, then you need to change the 8.2K (8K2) resistor until it is.

-Did you install a DC power jack -OR- are you only using battery power?
-What type of transistors did you use?

The color codes of the 1K and 10K resistors are right but I haven't tested them, but can they possibly make the whole pedal silent? Can I test it somehow or do you have to replace the resistors to find out if they were the problem?

Be sure you check ALL of your resistors and capacitors. Make sure they are the correct values and that they are installed properly. Especially the polarized capacitors. Check your wiring to the potentiometers.

Also, have a look at this wiring layout:

http://www.generalguitargadgets.com/pdf/ggg_ff5_lo_b69.pdf

This is specifically set up for Positive ground circuits which is what you are using. Notice that the V+ from the battery goes to the INPUT JACK and so on. You need to wire up your circuit like this diagram. NOT LIKE THE ONE YOU POSTED.

[andershp]

I don't know what you mean by "Q1 Collector should be biased around 1/2 of the V+ input" (sorry I'm danish so some of these technical words are a bit strange to me), but I guess it means that the voltage of the Q2 C should be half the 9V input voltage?

Yes. Your Q2 collector should be set to half of your input voltage. If you are using a wall plug, this may be higher than 9V. You need to use your DM and measure your input voltage then make sure you have half of that on the Collector of Q2. If not, then you need to change the 8.2K (8K2) resistor until it is.

-Did you install a DC power jack -OR- are you only using battery power?
-What type of transistors did you use?

The color codes of the 1K and 10K resistors are right but I haven't tested them, but can they possibly make the whole pedal silent? Can I test it somehow or do you have to replace the resistors to find out if they were the problem?

Be sure you check ALL of your resistors and capacitors. Make sure they are the correct values and that they are installed properly. Especially the polarized capacitors. Check your wiring to the potentiometers.

I forgot to mention that I replaced the 8.2K resistor with a 20K trimpot, since that was recommended on the site where I found the schematic: http://fuzzcentral.ssguitar.com/vox.php (at the bottom - "The PCB and Layout"). Adjusting the trimpot does not affect the sound (it doesn't create any sound), but I haven't tested the voltage on Q2 C when changing it (I will do that tomorrow).

I'm using DC Power jack, which is 9.26 V DC.

I used two AC128 Germanium PNP transistors - hfe 81-90 and hfe 111-120, since those values are recommended here: http://www.aronnelson.com/gallery/main.php/v/Richard-Boop-RLBJR65/album84/VoxToneBender.gif.html

I will check the rest later, but I don't have time right now - thanks for your help so far.

[Govmnt_Lacky]

...but I haven't tested the voltage on Q2 C when changing it (I will do that tomorrow).
I'm using DC Power jack, which is 9.26 V DC.

Definitely adjust the trim pot until you have half of input voltage (~ -4.63VDC) at the collector of Q2.

I will check the rest later, but I don't have time right now - thanks for your help so far.

No problem 

Jut be sure to repost with your findings. And, make sure you wire the circuit like the layout that I linked above. The one you posted is for NEGATIVE GROUND effects. This is a POSITIVE GROUND effect.

[LucifersTrip]

Q2
C = 7.38 V
B = 0.14 V
E = 0.10 V
==============

Forget about the fact that this is mis-biased, am I correct to think that if there is a voltage (7.38v) on the collector with E,B where they are that there should at least be some sound output...

....but he is getting "no sound at all"

Doesn't that suggest a mis-wiring/bad connection with the jacks or switch?

I would remove the switch and see if you get any sound first....

[andershp]

Also, have a look at this wiring layout:

http://www.generalguitargadgets.com/pdf/ggg_ff5_lo_b69.pdf

This is specifically set up for Positive ground circuits which is what you are using. Notice that the V+ from the battery goes to the INPUT JACK and so on. You need to wire up your circuit like this diagram. NOT LIKE THE ONE YOU POSTED.

I know that the circuit I posted is for negative ground:
I use a negative ground power supply, I reversed the polarized caps and the LED, and used PNP transistors. Shouldn't that be enough?

I'm not sure, but I can post a picture of the inside of the pedal?

Definitely adjust the trim pot until you have half of input voltage (~ -4.63VDC) at the collector of Q2.

The lowest value I can get on the Q2 C is 7.35 V, which is probably a problem with the trim pot..? Can that be the reason for the pedal being silent or should it (I would think so) make a sound at least..?

[Govmnt_Lacky]

I know that the circuit I posted is for negative ground:
I use a negative ground power supply, I reversed the polarized caps and the LED, and used PNP transistors. Shouldn't that be enough?

You are trying to use PNP transistors in a negative ground circuit. Although this has been shown to work SOME TIMES... it often produces bad results. You really need to wire the circuit as a POSITIVE GROUND (BTW, the circuit you referenced in your initial post IS IN FACT A POSITIVE GROUND CIRCUIT. You can tell because the + from the battery is going to the input jack Ring and the (-) from the battery is going to your 47uF/1K/10K junction.

You NEED to re-wire the circuit as POSITIVE GROUND. Look at the off-board wiring that I linked from GGG and install your caps like the schematic that you posted and you shoulds be fine. AC128 transistors are PNP. They need to be used in a POSITIVE GROUND circuit.

The lowest value I can get on the Q2 C is 7.35 V, which is probably a problem with the trim pot..? Can that be the reason for the pedal being silent or should it (I would think so) make a sound at least..?

This may be fixed if you change the circuit to POSITIVE GROUND.

[andershp]

I know that the circuit I posted is for negative ground:
I use a negative ground power supply, I reversed the polarized caps and the LED, and used PNP transistors. Shouldn't that be enough?

You are trying to use PNP transistors in a negative ground circuit. Although this has been shown to work SOME TIMES... it often produces bad results. You really need to wire the circuit as a POSITIVE GROUND (BTW, the circuit you referenced in your initial post IS IN FACT A POSITIVE GROUND CIRCUIT. You can tell because the + from the battery is going to the input jack Ring and the (-) from the battery is going to your 47uF/1K/10K junction.

You NEED to re-wire the circuit as POSITIVE GROUND. Look at the off-board wiring that I linked from GGG and install your caps like the schematic that you posted and you shoulds be fine. AC128 transistors are PNP. They need to be used in a POSITIVE GROUND circuit.

The lowest value I can get on the Q2 C is 7.35 V, which is probably a problem with the trim pot..? Can that be the reason for the pedal being silent or should it (I would think so) make a sound at least..?

This may be fixed if you change the circuit to POSITIVE GROUND.

Okay, I understand and I will try that out. However I can't rally figure out how to apply the positive ground circuit you linked to, since the actual circuit (not the true bypass wiring) is different and because the LED is installed on the PCB.

I thought about using the true bypass circuits from this site: http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=33&Itemid=27 - do you think that would be fine as well? Fx. one of these:

http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_tb_dcj_pnp.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_tb_dcj_pnp_gi.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_tb_dcj_pnp_ft.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

But I'm not sure wheter to choose the True Bypass/LED indicator DC Jack, the Input Grounded one or the one for positive tip power supply?

I don't no what input grounded means..?

I have a power supply polarity adapter, so that doesn't matter much, but would it be possibly the use this PNP pedal together with other NPN pedals if I used the non positive tip method?

[Govmnt_Lacky]

Can you link us to the vero layout that you used? You mentioned/linked fuzzcentral earlier but they only have PCB layouts. Did you create your own?

I think that your whole problem lies in the fact that you wired a NEGATIVE ground circuit and used PNP transistors.

If you can't link to a vero layout, I recommend that you post pictures of your build on the component and solder side of your board. Also, a pic of the off-board wiring.

Good Luck 

[andershp]

No, I created the layout myself. I think your right about the negative / positive wiring.

I will post pictures of each side soon...

Again I'm very much a newbie still, so it might not be the best work... but of course this is the best way to learn.

[andershp]

[Govmnt_Lacky]

You definitely have it wired for NEGATIVE ground which is not the way. You need to re-wire as positive ground. If you search here on the forum or on Google you will figure that out.

Also, I could not help but notice that your layout has NO TRACE CUTS  That is either a mistake or some excellent layout work!

[LucifersTrip]

No, I created the layout myself. I think your right about the negative / positive wiring.

as I wrote earlier, before you worry about any offboard wiring, the circuit should be tested first

you are just compounding problems and making it more difficult to diagnose if you wire switches, etc before you know that the circuit actually works

order: breadboard > test circuit > solder to board > test circuit > wire offboard > test circuit