Problem with Breadboard build

[guitarify]

So I have completely rebuilt this thing twice with the same result - no sound at all. One major clue is that I have never built a circuit from a schematic before, and this is the first time using a breadboard. So here are a few pics. I have 2 100K resistors in parallel since I didn't have the 47K. That should work right? I tried flipping the transistor around just to be sure I got that right, but still no luck. I'd appreciate any help figuring this out.

[diydave]

- multimeter and an audioprobe my friend. The two best tools in the world to debug your circuit. 

Measure your voltages on you transistor. If they are off, your transistor is misbiased.
If they are correct, there is something wrong with your signal line.
With your audioprobe you can trace back to where your signal is cut off.

Hope it helps

[Bad Chizzle]

It's hard to tell, but it looks very good. Your output wires may be reversed though. Like I said, it's hard to tell what's wrong without looking at the schematic.

[.Mike]

Assuming this is the Beginner Project...

I'm not sure if I'm missing it-- it's kind of hard to tell from the photos-- but I don't see any components actually connected to the positive rail of your breadboard.

Also, the schematic lists 5 resistors and a potentiometer. Since you are using two 100k resistors as a substitute for the 47k resistor, you should have 6 resistors. I only count 4 on your breadboard.

Did you possibly forget a couple of components?

Mike

[arma61]

Hi

I don't know that kind of breadbord but aren't you missing the "red circled" connections



on my breadboard those groups are all disconnected from each other, so I have jumpers between each 2

but again I don't know that RadioShack board.

A

[guitarify]

Thanks for the replies. Yes this is the beginner project. It still isn't working, but here is what I have done:
I noticed the missing resistor not long after posting so thats fixed. The 100K resistor at the bottom of the board was going to ground instead of the power rail-fixed. I thought I had tested that the power rails were connected but when I tested again I got nothing, so that is fixed.
So, lots of mistakes. But this is my first build so I kind of expected this process.
I don't know what voltages I should be getting at the transistor. I'm assuming I test by touching the multimeter to ground and each one of the legs? When I did that I got 190mv at the emitter and collector and .8V at the base.
If I understand the audioprobe idea correctly it's just moving your positive output wire up the circuit till you get no sound? I tried that and I lose signal after the first .1uf cap. That first cap also is what knocks the voltage to .8V, is that right? It's from Small Bear and is listed as .1mf but I read that, that's how Small Bear labels their caps -'m' for micro instead of using that greek symbol that looks like a 'u'.

[.Mike]

I noticed the missing resistor not long after posting so thats fixed. The 100K resistor at the bottom of the board was going to ground instead of the power rail-fixed. I thought I had tested that the power rails were connected but when I tested again I got nothing, so that is fixed.

Cool. So you should have six resistors total (since you are putting two 100K in parallel to make a 50K resistor).

So, lots of mistakes. But this is my first build so I kind of expected this process.

Yep, that's part of the fun.

I don't know what voltages I should be getting at the transistor. I'm assuming I test by touching the multimeter to ground and each one of the legs? When I did that I got 190mv at the emitter and collector and .8V at the base.

Take a look at this topic for sample voltages for the beginner project: http://www.diystompboxes.com/smfforum/index.php?topic=80734.0

If I understand the audioprobe idea correctly it's just moving your positive output wire up the circuit till you get no sound? I tried that and I lose signal after the first .1uf cap. That first cap also is what knocks the voltage to .8V, is that right? It's from Small Bear and is listed as .1mf but I read that, that's how Small Bear labels their caps -'m' for micro instead of using that greek symbol that looks like a 'u'.

The first cap is used to block the DC from traveling down your guitar cable and into your guitar, while allowing the AC signal from your guitar to pass into the circuit. The 0.1mF is the same as 0.1uF-- it's just how Smallbear labels them.

Keep at it. You'll get it going!

Mike

[guitarify]

Finally, it works!
After reading the debugging wiki where the different correct and incorrect voltages for a transistor were demonstrated. I realized my voltages there weren't right. So in tracing out from there I found I had yet another resistor going to ground that should have been powered.
As far as the sound, I can here no increase in volume whatsoever. It does start clipping when the pot is almost all the way up. Is that amp overdrive, or is the signal clipping somewhere in the circuit? Shouldn't I hear a change in the volume?

[guitarify]

So I tested a little further and this does boost the signal. I don't have a switch so had to unplug and plug it back in to hear the difference. But the pot seems to just add clipping. I never owned a boost pedal before so maybe this is how they work?

[.Mike]

It is supposed to be slightly above unity with the knob fully counter-clockwise, and should provide a fairly significant and noticeable boost with the knob fully clockwise. It should add some distortion at the far clockwise end of the rotation.

I had the same problem when I built mine (seems like ages ago), and it was a because I had the transistor in backwards. Double-check that.

Mike

[guitarify]

Thanks Mike. I tried reversing the transistor and it got louder but twisting the pot made no difference in volume till I got past the half-way point, then it cut out completely for the rest of the sweep. I also checked the transistor orientation 10 more times and it does seem to be correct the way I had it. I tried swapping some of the pot wires since I wasn't sure if it was important which way the signal went through the pot, but I didn't hear a difference.
Something must still be off somewhere..

[guitarify]

It's driving me a bit crazy that this only 'sort-of' works.
Besides the gain knob not really doing anything, though it cuts out completely turned more then 75%. I've noticed it also effects the volume knob on my guitar. The area from 9 to 10 is really sensitive with the volume seemingly doubling in that range.
Here are the readings from the transistor at this point:
C=3.7V
B=1.9V
E=1.3V
Maybe that will give some clue?
I tried the audio probe thing but didn't really know what I should be looking for. Most points gave no sound. And what I thought was weird was putting the probe before the circuit, essentially just connecting the two guitar cables together gave me nothing. Is this because of the capacitor on the probe?
I feel like I really can't attempt my next circuit till I understand what's going on here.

[Wild E]

Check your battery voltage. you may have drained it quite a bit through testing especially if it was wired wrong.

[guitarify]

Battery is fine 8.9V

[Wild E]

After studying your closeup pic(would've been easier if the holes were vertical & horizontal instead of diagonal) here is what I see. You said you fixed the 100k that was supposed to go to V+, good. Remove the yellow jumper between the 22u and 47u caps. you were missing 2 resistors; a 10k from collector to V+ and a 100k from the - side of the 10u cap to ground. As far as I can tell these changes should match the schematic. I hope this does it for you.

[guitarify]

Mike, your the man!
Thanks so much for taking the time to help me figure that out. The 2 resistors, I had already fixed. It was the yellow jumper. After I pulled it and it worked it took me a minute to figure out why because I was certain that wire needed to be there.
Then I realized that I was connecting to the center of the pot and that the purple jumper running parallel to the other purple jumper was making the correct connection to the first lug as it should.
I was very close to scrapping the whole thing and trying a different circuit. Thanks again!

[Wild E]

Glad I could help. Here's what I did which might help you in the future. I drew what you had connected to what on paper then I redrew it to make it look more like a schematic and compared it to the real schematic. Sounds too easy, huh? I don't know exactly how this messed up your circuit but I think it altered the biasing. Maybe someone with more knowledge can explain.