Tube Screamer need debugging help!

0ron124 · December 29, 2010, 01:10:50 PM

Hi all,

So here's the low down. I followed this post for the information http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
I believe it is a problem with the ground circuit somewhere.

1. When the curcuit is bypassed there is a clean sound. When you turn the effect on you just get dead silence however the power LED is on.

2. Effect: Tube Screamer w/ Expensive Boutique Mod by General Guitar Gadgets

3. http://www.generalguitargadgets.com/projects/17-distortion/82-its8-tube-screamer-808-replica-project

4. No

5. None

6. Ummm not sure

7. 9.05v
Voltage at the circuit board end of the red battery lead = 9.05v
Voltage at the circuit board end of the black battery lead = 9.05v

IC
1 = 8.5v
2 = 8.5v
3 = 8.5v
4 = 0v
5 = 8.5v
6 = 8.5v
7 = 8.5v
8 = 9.05v

Q1
C = 4.9v
B = 5.2v
E = 9.05v

Q2
C = 5.2v
B = 5.6v
E = 9.05v

D1
A = 8.4v
K = 8.2v

D2
A = 8.2v
K = 7.9v

D3 – Red LED
M (-) = 0v
P (+) = 8.5v

D4 – Red LED
M (-) = 8.5v
P (+) = 8.5v

D5
A = 0v
K = 9.05v

ayayay! · December 29, 2010, 01:24:57 PM

Go back and check your voltage divider: R9 & R10. Between those two resistors you should be getting approx 4.5v (that's the Vr in red on the schematic.) Everything everywhere in your debug list points to full voltage where it shouldn't be...

And it appears Q1 & Q2 are reversed.

0ron124 · December 29, 2010, 01:39:41 PM

Thanks for the speedy reply.

I checked the voltages between R9 and R10 I get 6.8v on both. As for the transistors I labled them backwards my bad...

Johan · December 29, 2010, 01:51:42 PM

do you have a cable plugged into the input. the black cable from the input jack to the circuit board should read 0volt, not 9volts,suggesting there is no monoplug plugged in or the jack is misswired.
J

ayayay! · December 29, 2010, 02:05:11 PM

Quote from: Johan on December 29, 2010, 01:51:42 PM
do you have a cable plugged into the input. the black cable from the input jack to the circuit board should read 0volt, not 9volts,suggesting there is no monoplug plugged in or the jack is misswired.
J

Ahh, I was wondering how he was getting that. That's a possibility, a TRS cable...

Quote from: 0ron124 on December 29, 2010, 01:39:41 PM
Thanks for the speedy reply.

I checked the voltages between R9 and R10 I get 6.8v on both. As for the transistors I labled them backwards my bad...

Something's not quite right there. Either you're using a 12v supply, or you've got a resistor that's maybe 1k and one that's 10k, something like that. Or the ass end of R10 isn't connecting to ground. Something funky is up there that I'm not getting... It doesn't explain why you'd have MORE voltage than that down the line...

Good to know the trannies are in right now. Have you remeasured them since?

0ron124 · December 29, 2010, 03:23:26 PM

Quote from: Johan on December 29, 2010, 01:51:42 PM
do you have a cable plugged into the input. the black cable from the input jack to the circuit board should read 0volt, not 9volts,suggesting there is no monoplug plugged in or the jack is misswired.
J

Yes I do have a cable plugged into the input jack. I also am getting 0 volts on the black wire into the board. So does that mean something is up with my cable?

Quote
Something's not quite right there. Either you're using a 12v supply, or you've got a resistor that's maybe 1k and one that's 10k, something like that. Or the ass end of R10 isn't connecting to ground. Something funky is up there that I'm not getting... It doesn't explain why you'd have MORE voltage than that down the line...

Good to know the trannies are in right now. Have you remeasured them since?

I'm using a boss PSU 9v adapter. If I remember correctly there was something funky going on with my ground. I'll check it out and post back.

I'll also remeasure them while I'm at it.

0ron124 · December 29, 2010, 06:17:15 PM

Ok so I just checked the voltages for the IC and the Trannies their the same as before. I also checked to be sure and both R9 and R10 are 10k resistors.

While I was at it I resoldered R9 and R10 just to make sure everything was good and rechecked the voltages. I have 5.6v on both of them and 9.05v before them.

petemoore · December 29, 2010, 06:25:02 PM

Check first that +/- are Not Connected.
Measure PS before, then after connecting it.
Voltage at the circuit board end of the red battery lead = 9.05v
Voltage at the circuit board end of the black battery lead = 9.05v
Because you are registering voltage at the opamp, I suspect this is a typo, both battery leads measuring the same voltage is either a miscommunication or sounds wrong, maybe I'm misreading it somehow.
It looks like the voltage divider isn't biasing the opamp Inputs and outputs.
What voltage do you measure where the two equal value divider resistors meet ?

twabelljr · December 29, 2010, 07:14:09 PM

Quote. I have 5.6v on both of them and 9.05v before them.

R9 sould have your source of 9.05V on one side and approx. 4.5V on the other side. R10 should have approx. 4.5V on one side and 0V on the other. Without R10 grounded on one end there is no voltage divider to provide your bias voltage.
Your voltage measurements at the IC show only a 0.55V drop.

PRR · December 29, 2010, 11:36:52 PM

> Voltage at the circuit board end of the black battery lead = 9.05v
> 1 = 8.5v
> 2 = 8.5v
> 3 = 8.5v
> 4 = 0v
> 5 = 8.5v
> 6 = 8.5v
> 7 = 8.5v
> 8 = 9.05v
>
> Q1
> C = 4.9v
> B = 5.2v
> E = 9.05v
>
> Q2
> C = 5.2v
> B = 5.6v
> E = 9.05v

You got plausable (a bit high) voltages at Q1 Q2 Bases.

> between R9 and R10 I get 6.8v on both

Ah, There is a short between the _IC_ ends of R5 R16 and VR. (Figure R9 as really R9||R5||R16: 6.8V.)

Is your IC in right-way-round?

0ron124 · December 29, 2010, 11:51:04 PM

Ok so I got it working! Thank you all for your help. I turns out R10 was registering at 5k ohms instead of 10k which it is marked at as well as a bad IC. I just swapped the IC with a spare I had and it was good to go. Thanks again everyone sounds awesome!

ayayay! · December 30, 2010, 10:01:25 AM

Bingo! Awesome man, congrats! Nice work on debug posting too.

0ron124 · January 02, 2011, 07:29:22 PM

Ok well apparently I spoke too soon. I should have tested the tube screamer more throughly. I discovered it wasn't working again after I decided to put it in it's enclosure. Anyways, the new problem is when the effect is engaged there is very little distortion and with the gain knob at full bast. Here's the new voltages.

IC
1 = 4.5v
2 = 4.5v
3 = 4.5v
4 = 0v
5 = 9.05v
6 = 4.5v
7 = 4.5v
8 = 4.5v

Q1
C = 9.05v
B = 3.76v
E = 3.31v

Q2
C = 9.05v
B = 3.98v
E = 3.63v

D1
A = 4.07v
K = 4.5v

D2
A = 4.5v
K = 4.3v

D2b (in series with D2)
A = 4.3v
K = 4.14v

D3 (Red LED)
P (+) = 4.5v
N (-) = 3.3v

D4 (Red LED)
P (+) = 3.3v
N (-) = 4.5v

D5
A = 0v
K = 9.05v

twabelljr · January 02, 2011, 10:02:01 PM

Did you mix up IC voltages 5 and 8? they seem backwards. Typo maybe??

0ron124 · January 03, 2011, 09:42:40 PM

Oops...yeah that was a typo on my part. Thanks for catching it. Anyone have an idea of what's wrong?

PRR · January 03, 2011, 10:46:32 PM

> it wasn't working again after I decided to put it in it's enclosure.

So what changes when you put it back in? Usually busted or loose wires. Sometimes unecpected grounding.

Stuff like that, you have to find by inspection.

ayayay! · January 04, 2011, 09:20:50 AM

Seems to me you've done some good t-shooting to this point, but it's time you build a probe and trace this thing audibly.

http://www.diystompboxes.com/pedals/debug.html

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Tube Screamer need debugging help!