Effect doesn't work.

[supernaut]

Well I completed my first pedal. But I am having troubles.

This is the schematic: http://www.geocities.com/j4_student/voxtreb.jpg With the .47uf capacitor I used an electrolytic one as a replacement.

My first issue was that I would not get any sound when bypassed and when engaged I got almost no change (maybe a tiny bit more trebley but hardly any boost in output). So I took it back and had a look at it. I had the ring and tip mixed up for the input jack. I also noticed a poor connection between the first leg of the 22k resistor and the transistor. Which was understandable as I think I burnt the crap out of the copper on the stripboard due to soldering and de-soldering a lot because of mistakes. So I bridged that by soldering a cut-off leg of one of the components. Now when I plug it in it is fine bypassed (even a bit louder I noticed, which is strange) but when it is engaged it gets very quiet. I have made sure that the volume pot is on full, and I do know that the pot works as it goes off completely when turned down. What could be my problem here?

[supernaut]

I got some voltage readings as well. The battery is giving 9.48v and at the point where the positive is connected to the board is 9.47v. I am not quite sure how to measure negative as it is connected to the ring on the input jack. Is that where I get the reading from?

As for the transistor,
C = 5.41v
B =1.58v
E =.93v

And I am sure it is wired in right as I checked the pinout online.

[frokost]

Hi. Try with an audio probe, trace the signal through the circuit and find out where it gets lost. As for voltage readings, the black lead goes to ground.

[supernaut]

Okay I'll do that, but what is an audio probe? Also do those transistor voltages look right?

One more thing I probably should have mentioned, the switch is dpdt and it's hooked up for true bypass.

[frokost]

As far as I can tell, the voltages are OK.

An audio probe is decribed in the debugging page on top of every page: http://www.diystompboxes.com/wiki/index.php?title=Debugging

A DMM, an audio probe and the procedures in the debugging thread ("DEBUGGING - What to do when it doesn't work") will get you through a lot of debugging on your own.

[R O Tiree]

Well, I just simulated it, and those voltages are absolutely spot-on.

Check that you have the electrolytic caps the right way round. The 10µF cap should have its positive pin connected to the emitter of the transistor. The 0.47µF cap should have its positive pin connected to the junction of the two 2k2 resistors (2.2k).

You might have burned out a cap or the transistor if you had the iron on the joints for a long time... although if the transistor had been heat damaged, I wouldn't expect those pin voltages to be as good as they are.

[Myriad Society]

Supernaut, I have not built this effect before so am not sure what the end result is supposed to be but will offer my best guess. The voltages you have listed for the transistor appear to be correct for the circuit so I would believe that all is correct in the circuit up to that point at least.

I would take a voltage reading on the leg of that .47uF cap that is closest to the 2.2K resistors. If you are getting a reading that is the same as your Collector reading on the transistor (5.41V) then you have the capacitor connected in the wrong place - between the bottom 2.2K resistor and the collector.

Based on calculation, I would expect the voltage reading going into this capacitor to be approximately 7.4V when connected at the midpoint of the 2.2K resistors with a 9.4V source voltage. Possible this may be the reason for your loss of output.

[R O Tiree]

If you connect the cap directly to the collector, the output increases. In fact, it doubles - not surprisingly, given identical resistors.

[supernaut]

I just measured that cap and I get a reading of 7.48v

Also I just did a voltage reading on the ground and got nothing, is that normal?

And thanks for all the help, you guys are awesome.

[frokost]

Ground should read 0 volts, so that's fine.

[petemoore]

Also I just did a voltage reading on the ground and got nothing, is that normal?  
 If you clip the black lead on Gnd. and measure to any and all grounds, you should measure 0.0v potential. [yes].

[supernaut]

Okay, then what I will do is get the parts for an audio probe tomorrow and see where the problem lies.

[frokost]

In essence, an audio probe is just a capacitor with some infrastructure  . Meanwhile, you can do the usual stuff: Double and triple check your wiring, look for solder bridges and components of the wrong value. Pictures of the build and a link to the layout could help too.

[supernaut]

I tried pictures but they didn't come out all that well. I really need a new camera. As for the layout, I worked it out on my own. I will definitely be double checking wiring in the meantime though.

[supernaut]

Sorry to bring back such an old thread but I am still having trouble. I have tried the audio probe and can't really pinpoint any issues with that. I have managed to get it to work briefly however. I plugged my mp3 player into the input and as I was playing with the input a bit, it suddenly started working. It also cuts out every now and then but if I can leave it in a position where it works it won't stop working unless moved. At first I noticed some weak soldering on the lugs, so I re-did them but still the same problem. However what is really weird is I cannot get it to work at all with the guitar, only the mp3 player. It can't be the guitar either cos it works fine otherwise and with other effects pedals. I also tried a second guitar and still nothing. Sorry to keep asking questions about this but I am all out of ideas.

[petemoore]

  Audio probe is the 'opposite' of an Audio Injector.
  The injector is a source [tape a key down on the play-keyboard organ, or strum guitar all day, find other constant output source]...through a capacitor [to Block DC], will put an AC signal into your Probe type thing [DMM wire/probe or...wire...]
  Try thumbuzzing it from the output, use a probe to connect your thumb to the output cable tip [use this stupid idea for HV only on low voltage circuits of course], work your way up to and then through the next to last component, note differences if signal drops or...
  When you get to the transistor, the base should sound louder than the collector.
  Keep going, see if you can find where the signal drops out.
  The voltages look 'reasonable', so the transistor is probably amplifying [verify that it is using...whatever you can !] some perhipheral item is probably the lossage culprit.

[nosamiam]

Sorry to bring back such an old thread but I am still having trouble. I have tried the audio probe and can't really pinpoint any issues with that. I have managed to get it to work briefly however. I plugged my mp3 player into the input and as I was playing with the input a bit, it suddenly started working.

Could this part have something to do with the mp3 player being stereo and the guitar being mono?

[spaceace76]

Sorry to bring back such an old thread but I am still having trouble. I have tried the audio probe and can't really pinpoint any issues with that. I have managed to get it to work briefly however. I plugged my mp3 player into the input and as I was playing with the input a bit, it suddenly started working.

Could this part have something to do with the mp3 player being stereo and the guitar being mono?

Wouldn't the mp3 player have a much higher output? If that's getting sound through then maybe a transistor isn't amplifying. Double check your pinouts, soldering, orientation, swap them out for new ones, etc.

[frokost]

I have tried the audio probe and can't really pinpoint any issues with that.

How do you mean? With the audio probe, trace the signal all the way from the input jack and work your way through the circuit. Where there no signal is, your problem lies, as Yoda would say.