OVERDRIVE HELP

[joakinrox]

Hello, i built a tubescreamer using the layout in marks gallery. but i am having this weird issue i cannot understand,

when i wired and finished the pedal i went ahead to test it, and in bypass it worked fine but when turn on the effect i get no sound whatsoever. to debug, i used the audio probe featured at geofex, and in bypass i could hear the guitar fine using the probe, but as soon as i turn on the effect the signal dies completely, not even touching the tip of the guitar cable with the probe gives me any sound. naturally i though i had a short to ground or something, but when i check continuity with my dmm to ground i get no shorts.


can anyone tell me what kind of problem could be causing the whole signal to die when i turn on the effect? so i know where to look, i've been at it for 3 days but i dont get it. thanks!

[Jdansti]

Welcome to the forum!

There are several things that could be causing your problem.

Here's the quick check:
1) Check for power when you turn it on and make sure the polarity is correct. 
2) Check for a good ground path to all grounded components including input and output jacks. 
3) Check the polarity of diodes and polarized capacitors (including any tantalums). 
4) Check that your pots are properly wired.
5) Check that your bypass switch is properly wired. 
6) Check for solder bridges, cold solder joints, and for places that are not soldered (were missed). 

If you don't find anything in the steps above, go here and follow the debugging process:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[joakinrox]

OK, following debggind process:


circuit: tubescreamer 808

http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/TS808_TubeScreamer_LAYOUT.gif.html layout


part substitutions:

c5, c6 c20 and c2 are electrolytic caps, c7 is tantalum, r12 is 2 megs instead of 2.2. for c3 i used two ceramic caps in parallel (33 and 22 pf)
for the polarity protection diode i used a 1n4148 instead of a higher current one.
pots are all linear, but for the level one i used the tapering resistor R.G. describes in his website to simulate a logaritmic response.


VOLTAGES:

the transistor pinout is acording to this datasheet:

http://www.fairchildsemi.com/ds/2N/2N3904.pdf
i soldered the trnsistors as showed in the layout


the IC pinout is acording to this datasheet:
http://www.alldatasheet.com/datasheet-pdf/pdf/25389/STMICROELECTRONICS/TL082CN.html
i used many op amps the 072, an rc 4558, and some other dual op-amps i dont remember. the voltages were measured with the tl 082


Q1
B:8.33
E:8.31
C: 9.01

Q2
B: 8.34
E: 8.32
C: 9.02

IC1
1: 5.78
2:5.79
3:5.78
4:0v
5:5.8
6:5.79
7:5.79
8:9 v

d1
a 5.04
k 5.04

d2

a 5.04
k 5.04

d3
a 0
k 8.98


thx in advanced for any help

[Quackzed]

check that r2 r15 are grounded on their ground side.
r12 swap is fine
but the voltages look like neither transistors emitters are right...also you could double check pinout of the trannies...

[caspercody]

The Tubescreamer uses a 2SC1815, and you are using a 2N3904. I do not remember if these are compatible replacements. But the base and collector  pins are different.

2SC1815
1=emitter
2=collector
3=base

2N3904
1=emitter
2=base
3=collector

I remember having to twist those two legs to get the base and collector switched. Then mine worked.

[AudioEcstasy]

I had a similar issue with my first build, turns out it was something grounded that should not have been. One little thing can be all it takes! I would say check your grounds and solder joints

[Jdansti]

If you're still having problems, please post photos of both sides of the board and try to include the off board components if you can so we can see how they're connected.  Thanks!

[joakinrox]

OK, SOMETHING WEIRD HAPPENED, following your recomendations i checked the trannies pinouts and they were in fact correct, but i went ahead and changed them anyways, before i puted them in the circuit i tested them in the breadboard to turn on a led, and not a single one worked, i purchased like 20 and they were all brand new and none worked, so i used some other npn trannies i had around and now my ts-808 is working. but i'm now wondering, why none of the 2n3904 works? is it posible to have something like a "fake" transistor?

they're not mosfets so they could not have damaged from regular handling right?. Anyway, thanks a bunch for your help.


PS: i have some noise when i turn up the volume, any recommendations to reduce it?