Troubleshooting help on an Octave Pedal

[aweeks]

1.What does it do, not do, and sound like?
  In bypass mode, I'm getting a clean signal.  When I turn on the effect I get a buzz similar to when touching the tip of a guitar cable plugged into an amp.  I do get signal from the guitar, but it's a degraded volume, and the effect just sounds tin-ey.  Also, when I touch the metal enclosure, the buzz gets a little louder.

I keep going over my solders, double checking them in hopes I can find the issue by accident.

  I am a relative novice to electronics (at least this type), so if I've missed collecting any information or it's not presented the right way, have a little patience.  Also, than you in advance.

2.Name of the circuit =
   GRO Dan Armstrong Green Ringer Replica from General Guitar Gadgets

3.Source of the circuit (URL of schematic or project) =
   Description: http://www.generalguitargadgets.com/projects/22-octave/131-green-ringer?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
   Schematic: http://www.generalguitargadgets.com/pdf/ggg_gro_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
   Build Manual: http://www.generalguitargadgets.com/pdf/ggg_gro_instruct.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
   The Build manual lists some circuit values.


4.Any modifications to the circuit? NO

5.Any parts substitutions? NO

6.Positive ground to negative ground conversion? No idea.

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 8.9

Voltage Readings.  Any values provided by the build manual are in (parenthesis) next to my value.
Q1
 C 4.84 ( 5.5 )
 B 1.71 ( 1.8 )
 E 1.35 ( 1.1 )

Q2
 C 3.17 ( 2.6 )
 B 4.84 ( 5.5 )
 E 5.55 ( 6.2 )

Q3
 C 8.80 ( 8.8 )
 B 3.89 ( 4.0 )
 E 3.58 ( 3.4 )

C1 (For the C's and D's I guessed at the positive and negative side.)
 + 1.7
 -  0.0

C2
 + 5.52
 - 4.06

C3
 + 4.06
 - 3.18

C4
 + 8.77
 - 0.00

C5 (This capacitor looks different than the rest. The others, and the one in the build manual, are brown and round-ish.  This one is blue and rectangular.  After a quick search on google, it appears to be the right capacitor.  I also wanted until the end to solder this one on just to make sure I wasn't missing something.
 + 3.56
 - 0.00

D1
 + 4.05
 - 3.87

D2
 + 4.05
 - 3.87

[Mark Hammer]

Your first step should always be to try and identify how far the signal gets, using your meter.  The voltages on the transistor pins can often be a useful indicator of why something sounds awful or just generally "wrong", but remember you get those voltage readings even without anything plugged into the circuit, so they don't always give an indication of where the signal "stops".

So, what to do?

Plug any continuus source of signal (e.g., the headphone output of an MP3 player) into the circuit, so there's something to measure that still leaves you with 2 fee hands to do other things.  Get your meter, set it to an AC range (if it is not autoranging) that will let you measure AC voltages up to a few volts.  Clip your black meter-lead to a dependable ground point on the chassis or circuit board.

You can now use your hot/red probe to see if there is signal appearing at any of a variety of checkpoints.  So, if you bypass switch is working OK, you shold be able to measure AC on the switch terminal where the wire going to the board connects, as well as the point on the board where that wire goes to.  If there is an input cap on the board, you shold be able to measure AC on the "other" side of that cap, before it gets to any semiconductor.  YOu should be able to measure AC on the output and input of any semiconductor used.  And so on.  In other words, you pick spots to measure and identify where the signal "stops".

[aweeks]

My multimeter only has 200V and 500V AC settings and neither pick up a reading from my guitar. 

A buddy of mine pointed me here:  http://diy-fever.com/misc/audio-probe/

I'm gonna try this.

[Jdansti]

The audio probe is useful, but what Mark is saying is you could plug a "noise maker" such as an MP3 player instead of a guitar into the input of your circuit so that you'll have a high enough signal to measure.

[aweeks]

Thank you. That makes sense. 

I think I found the issue.  I soldered the 2 diodes on incorrectly.  However, in the process of removing and resoldering them, I think I fried them.  They are now dead.

[aweeks]

Wasn't the issue.  Took it to a buddies place.  We cleaned up some of my soldering, re-soldered a couple of things.  Some of the buzz went away, but it's distorting and doesn't sound right.  What we found, from using the audio probe is that it gets noisy and funky between the 2 diodes and Q3.  He had replacement diodes, so we tried replacing those.  No luck.  Might try replacing Q3 tomorrow. 

Anyone?  Thoughts?  Ideas? Tips?

[Jdansti]

Would it be possible for you to post some photos showing both sides of the board and all of the off board connections?

[aweeks]

[Jdansti]

Thanks for the pics. I need to sit down and trace your wiring and examine the board. Unfortunately the wife unit has me busy today. I'll try to get back to you today, but it might be tomorrow.

BTW-looks like you've shed some blood on your bench working on this! 

[aweeks]

I would love to say that's blood.. sadly it's just stain from a different project.

[zambo]

Is that stain from your amp? If you got time i will be home all day building. See if ratshack has a new 2n3906 and we could test it some more if you like

[Jdansti]

I didn't see anything glaring that would be a problem.  I made some notes on the photos. These things are probably OK, but I noted them mainly because they were not clear in the photos.







Double check all of your grounds.  [EDIT: Do this with no power connected.] If you have a meter, set it to continuity or resistance (ohms) and place one probe on a ground pad of the PCB, and check the grounds on all jacks including power. Also check the switch ground.

Make sure that the three transistors are in the correct locations. Q1 and Q3 are NPN and Q2 is PNP.  Check that Q2 is the PNP.

If all of the above doesn't indicate a problem, then you might want to start checking the transistors as Zambo suggested.

[LucifersTrip]

I'd just like to give a few, hopefully helpful pieces of info.

1) here are other working voltages


2) when troubleshooting, it's always good to get it down to the simplest form....so, it'd be a good idea to eliminate the switch from the equation until fixed

3) out of the LOADs of pedals I've built, the GR is one of the few that didn't sound good with a power supply. Other DIYers have had the same problem...hum, sh*t quality degraded tones, etc....the solution was from PRR:

"The fast/simple fix is to bring the power in via a 100 ohm resistor so that the 100uFd C2 has some leverage against the power supply ripple."