First Project Gone Wrong -- ModKitsDIY ThunderDrive Pedal

[chowman29]

Hi everyone!

I've been lurking around these forums for a bit too long as of now, and am in desperate need for some help and advice.

As embarrassing as it is, I am having difficulty getting the seemingly very-easy-to-put-together ThunderDrive pedal (from ModKitsDIY). For the record, I did not purchase the DIY kit from this site, but rather bought the parts on my own from my local RadioShack, Fry's, and had some lying around from previous projects (all of which were functional prior to assembly, and match up exactly or nearly exactly with the values listed on the parts-list for the pedal). Here is a link to an image of the schematic for the pedal: http://www.modkitsdiy.com/sites/default/files/product_files/the_thunderdrive_schematic.pdf

Instructions that I followed: http://www.modkitsdiy.com/sites/default/files/product_files/k-950_thunderdrive_instructions.pdf

So here is where I list all the problems I'm having...

The pedal works fine when bypassing the circuit. When I push the footswitch, clean sound will come through my amp (with some fuzz/feedback noise, though). However, when I press the switch again, all I get is fuzz with absolutely no guitar-sound coming at all, no matter how softly or loudly I strum the strings. When I touch the strings on my guitar with my finger, however, or any of the components in the circuit, I will hear a pop sound, but that's it.

There is a distortion knob and output (volume, I'm assuming) knob on the pedal. When I turn the output pot all the way to the left, the fuzz sound gets quieter. Same when I turn the knob to the right, the fuzz sound volume increases, which means that the output pot is fine, I'm assuming. Turning the distortion knob does not affect the fuzz sound at all. I also pulled out an old multimeter and got to testing some voltages and current-values in the circuit and compared my values to those shown in the schematic. Here is when I knew something was definitely wrong. I have also checked over and over again to make sure that I have followed the instructions correctly and that my transistor is facing the right way (so as not to confuse the Emitter, Base, and Collector leads).

My values / Schematic's values
E: 8.61V / 0.0V
B: 3.06V / 0.6V
C: 9.14V / 3.2V
PWR: 9.14V / 9.3V

Yeah... I don't really know what's going on with the transistor at all. What I did want to bring up to attention is that the capacitors I'm using have 104K written on them, not 104J as called for in the spec. Both are .1uF capacitors, but the ones I'm using are rated for 10% tolerance, versus the 104J which I believe is rated at 5%. Would this be the problem? I've read nearly all the write-ups on debugging transistors and what the correct values should be on this forum and around the Internet, but no matter what I've done, I can get these values to change.

The schematic also shows the current through to the 4.7K Resistor to be 1.3mADC @ 9.3 VDC. When I test with my multimeter, I get a value of 1.98mADC. Now, my value for the current seems to make sense to me with my very elementary and limited knowledge of circuits...
If V = IR, with my 9.14V battery and 4.7K resistor...
9.14V = I * 4700ohm
I = 1.944mA, which is pretty close to what I'm getting (1.98mA). Eh, I wouldn't trust myself or call this a proof of any kind at all, since I have no idea whether or not I'm doing the calculation right or whether or not I need to take the capacitors or 2M resistor into account as well...

I've tested all the values with a guitar cable plugged in the input, in the output, in both input and output, with the switch pressed once, then pressed again, and with both knobs turned fully in both directions. No matter what I do, the values I get are consistent. Consistently wrong, unfortunately for me. I've also re-melted my solder joints a few times to ensure that I had solid connections everywhere, and made sure hundreds of times that no components/leads are touching things that they shouldn't be touching, so I really have no clue what to do or where to go from here.

Hopefully the experts and people who have been in my situation before can offer their two-cents to try to help me fix my situation! I will be more than happy and willing to post any additional information that will help you help me

[aron]

First question - is your battery wired backwards? Why are you getting negative numbers for the voltages? Also, the emitter (E) should be connected directly to ground (that's why it's zero volts).

[chowman29]

Oh sorry, those aren't negative signs, they're supposed to be dashes, but I'll edit that to make it more readable. Sorry about that again!

Hmm, I'll have to look into that emitter problem. I'll come clean and say I didn't know anything I was doing while assembling the pedal, and just followed whatever instructions I was told by the manual :\

[Gus]

I looked at the links.  I saw the emitter is grounded by a mechanical connection.  The mount for the terminal strip to the box and then by the input jack. 

Remove the battery and check with a meter that the emitter is grounded and connected to the input jack and the black battery connector lead with an input jack installed.

The schematic does not match drawing 4 the input jack ground switching is not shown.

I just posted some stuff about simple circuits like this.   

[smallbearelec]

Hi--

Something is not wired right. This new article:

https://www.smallbearelec.com/HowTos/BeginnerArticle/BeginnerDos.htm

covers some typical mistakes that beginners make in selecting a first build, and a little about what to do if/when you hit a land mine. I presumed in writing it that you would be building on some kind of board as most people do, but my suggestion for troubleshooting is the same: Make clean copies of the schem and layout. Then start at the input on the schem and use the continuity function of your multimeter to make sure that every point that you think should be connected Really Is. Mark off connections with a highlighter as you test.

This is a vetted build, and it is right in difficulty level for a beginner. I would have suggested that you pay for the kit so that all of the parts can be presumed to match the layout Exactly, but you can probably make do with what you have. Let us know how the fault-finding goes.

[LucifersTrip]

C: 9.14V / 3.2V
PWR: 9.14V / 9.3V

you have C connected directly to the (+) supply?

try posting some clear closeup pics and someone will most likely spot the error