Marshall guv'nor replica problem (maybe)

[bdsbigfoot]

First post -- love these forums.  I hope someone out there can help me....

I built a guv'nor replica from a kit that I bought from general guitar gadgets and I think there is something not quite right about it.  It works, but I just didn't think it had nearly as much 'gain/distortion' as I expected, although I had never used a Guv'nor pedal before so didn't know for sure.  The build guide on GGG has voltage measurements that I should expect on the 8 pins of the IC.  All of my pins are pretty much dead on EXCEPT pin #3.  The GGG site says I should see around 4.2v at pin three and I only have around 2.3v.  I emailed back and forth a few times with JD and everything he asked me checked out, then he said he had no other suggestions for me.  Since then, I have replaced some of the components that connect to pin 3 (thinking that some components may have been labeled incorrectly) and I have the same situation.  One thing that JD said to me was that the guv'nor kit should have as much distortion as a Distortion +.  I had never played one of those either, but I just finished building a replica and the D+ definitely has more distortion than my guv'nor.

I am sort of new to pedal building and I have no idea what pin 3's function is, but if my voltage is half of what it is supposed to be, then it seems to me that the pedal would not function properly.

Anyone have any thoughts on this?  Maybe someone out there has built this kit and could measure their pin 3 for me to compare with??  Other suggestions/info would also be appreciated.

Thanks!!

[GibsonGM]

Hey BD, welcome to the addictive world of pedal building!  Have you checked the thread in the build your own stompbox forum (near the top), called "Debugging - what to do when it doesn't work"? 
1) Fill out the "questionnaire" with voltages, first.
2) make an audio probe (search the forum if you need instructions)

IC is a TL072, right?  That's a dual opamp.  2 amps in one.  Pin 3 is the non-inverting input, and has Vref on it, so I'd expect about 1/2 battery voltage should be there.  It's also your input, so audio probing there while playing a note should give you a sound.   It's probably a solder bridge or missed connection, very easy to do even after many builds.

Did you socket the IC, or solder it right to the board? Sometimes they're overheated that way and can get zapped.  So, check for solder bridges between traces on the board, between the pins of the IC, too.  I'd put in a socket if you don't have one, and replace the TL072.   
Read the debugging thread, and walk your way thru the circuit w/audio probe while someone plays your guitar...let us know where the signal dies.    You'll get it working, keep at it!

~Mike

[bdsbigfoot]

Thanks for chiming in -- I must admit that I am somewhat addicted to building pedals already (built 5 distortion/overdrive units so far -- all with good to great results).

I will do a bit more homework (i.e. answer the questions on the debugging thread) tonight, but I can affirmatively say that the IC is a TL072, but I don't have any spares sitting around to swap out.  Would need to order one.

Also, I already built an audio probe for a previous project that didn't work (this one had no sound at all at the output).  My thought process with the guv'nor was that since there was sound at the output, then the audio probe would not serve a purpose, but it seems that the probe can even serve a purpose for a pedal that has sound, just not quite the right sound.

Lastly, I used an 8-pin socket for the IC -- I learned that tip with my first build.

[GibsonGM]

Yeah, something is definitely wrong, the guv'nor should be pretty high into overdrive/dist land.  Usually this sort of thing is builder error - crossed solder bridges, cold solder joints, a simple mistake that's easy to make after spending a few hours looking at tiny parts!   So you have to get out the magnifying glass and a bright light :sigh:   Each time you find one of these glitches, you learn something, and next time it goes faster!

For an audio probe, I used a plastic square stereo jack.  I have a lead on the sleeve (barrel) that I connect to circuit ground with an alligator clip (battery "-" usually)....tip is a red wire, has a .22uF cap folded over the body of the jack and soldered, then taped to the plastic body....from there the wire goes out about 12" to an insulated alligator clip that I chuck a small length of wire into to probe.    Same with the ring side (allows dual inputs if I want, I usually just have it taped up out of the way).    Maybe the cap on yours is shorted to itself? You have to make it really stable.   Best tool on my bench )   The cap is important to keep DC from entering your amp - it makes a crackle when you encounter it but can't go by the cap. 
If you can narrow down the area where the signal stops, that's the place to check component values, orientation, solder quality/bridging....
I'll take a look after you've probed....
Consider making an order to Smallbear and getting a selection of opamps etc.  Gotta have a spare parts bin for those late-night "I wanna build that now!" fits!