I built a Tube Screamer and it has a very low volume output

[kraigen]

I can confirm the transistor pins are right. This is the schematic I followed (I used a PCB, btw): http://effectslayouts.blogspot.mx/2015/02/ibanez-ts808-tube-screamer.html

[Kipper4]

That is a layout. Not a schematic.

There's a true bypass schematic on this page

http://www.electrosmash.com/tube-screamer-analysis

And an explanation of the different stages.

I can't guarantee it's the one used in this layout.

One the input buffer I'd probably expect ( same for output buffer )
C=9v
B=3v ish
E=2v5

YMMV

[kraigen]

I'll keep those two terms in mind from now on. The problem appears to be in the input buffer, there are mV in all of the pins, the voltages at the output transistor are the following:

C: 9.1 v
B: 3.6 v
E: 3.1 v

[kraigen]

I probed around the transistor and there was sound everywhere, and the resistor values are correct

[GibsonGM]

So, there are only mV at each pin of the input buffer transistor....but there is a much louder signal than your input at pins 1 and 6 of the opamp?   You should see 9V on the collector.   

Try to measure the voltages of the input transistor again, if so, ok?

If your signal on pin 1, pin 6 is much louder than the input, that means the 2 amplifier stages in the chip are operating (maybe not properly, but they are at least amplifying).  If the first transistor was defective, it should not pass signal to them.   Its job as a buffer means the signal coming from it would be just about the same level as what is at the input.

If you have high signal level at pin 6, and low signal at the volume pot, that suggests a problem in between them.  A bad output cap, or perhaps the pot is bad or requires cleaning and/or resoldering of the lugs.      If all is well at the pot, I would suspect the output buffer.    There can always be another error, such as a part wrong-way-around, or a solder bridge done by accident.

Stick with it, eventually you will find the problem.  In the process, you learn how the circuit works! 

[kraigen]

So, there are only mV at each pin of the input buffer transistor....but there is a much louder signal than your input at pins 1 and 6 of the opamp?   You should see 9V on the collector.   

Try to measure the voltages of the input transistor again, if so, ok?

If your signal on pin 1, pin 6 is much louder than the input, that means the 2 amplifier stages in the chip are operating (maybe not properly, but they are at least amplifying).  If the first transistor was defective, it should not pass signal to them.   Its job as a buffer means the signal coming from it would be just about the same level as what is at the input.

If you have high signal level at pin 6, and low signal at the volume pot, that suggests a problem in between them.  A bad output cap, or perhaps the pot is bad or requires cleaning and/or resoldering of the lugs.      If all is well at the pot, I would suspect the output buffer.    There can always be another error, such as a part wrong-way-around, or a solder bridge done by accident.

Stick with it, eventually you will find the problem.  In the process, you learn how the circuit works!

The voltage on the input transistor is still in the mV range, I have already checked for solder bridges and cold joints with the multimeter, to no avail.

[GibsonGM]

You are sure you are measuring the right transistor, and it is the INPUT buffer, not the output, that is mV in values?  Not even the collector is at 9V??   If this were the output transistor, there is your problem.  No 9V at the collector = transistor totally shorted, maybe.  Odd that it is passing signal, a true short would not allow that.....


The tricky thing is that, even if Q1 is not functioning, you will still have a reasonable gain thru the opamp and as long as signal is input, it will amplify it.  Q1 is just a buffer - some designs based on the TS don't even include it - the pedal runs fine.   Leave Q1 for now I guess, as long as you are SURE that is the input transistor and not output.

Since you have a MUCH louder signal at pin 6*, I would follow that along til I found where it drops suddenly.   Some build error around the last transistor seems likely, so search those out, as well as all resistor values and correct transistor orientation...

* pin 6 should be VERY loud, as loud as you'd expect the pedal to be when vol. it turned up 100%.  Well above unity.

[kraigen]

Pin 6 is not that loud, I'll probe around that.

[kraigen]

You are sure you are measuring the right transistor, and it is the INPUT buffer, not the output, that is mV in values?  Not even the collector is at 9V??   If this were the output transistor, there is your problem.  No 9V at the collector = transistor totally shorted, maybe.  Odd that it is passing signal, a true short would not allow that.....


The tricky thing is that, even if Q1 is not functioning, you will still have a reasonable gain thru the opamp and as long as signal is input, it will amplify it.  Q1 is just a buffer - some designs based on the TS don't even include it - the pedal runs fine.   Leave Q1 for now I guess, as long as you are SURE that is the input transistor and not output.

Since you have a MUCH louder signal at pin 6*, I would follow that along til I found where it drops suddenly.   Some build error around the last transistor seems likely, so search those out, as well as all resistor values and correct transistor orientation...

* pin 6 should be VERY loud, as loud as you'd expect the pedal to be when vol. it turned up 100%.  Well above unity.

Pin 6 is well above unity, but pin 1 is the one that sounds loud as hell.

[GibsonGM]

Boy did I steer you wrong - pin 7 should be very loud, it is the output for the 2nd opamp stage, not pin 6.  Sorry 'bout that.  If that is also very loud (a great sign), then your problem is past that, with the output buffer or its supporting parts.

It could be as simple as no voltage to the transistor, a solder bridge, transistor in backwards, wrong value resistor...bad pot (audio probe each side of the pot > input, wiper, be sure other end is at 4.5ish volts).   Take the path that is simplest...audio probe the pot, the base and emitter of the transistor...is the 510k going to the base, other end to 4.5V?     Check emitter output - be sure all resistors/cap are installed properly. 

This is why tagboard debugging is more difficult....if you have sound at the IC, you WILL find the error, tho, with patience!

[kraigen]

Boy did I steer you wrong - pin 7 should be very loud, it is the output for the 2nd opamp stage, not pin 6.  Sorry 'bout that.  If that is also very loud (a great sign), then your problem is past that, with the output buffer or its supporting parts.

It could be as simple as no voltage to the transistor, a solder bridge, transistor in backwards, wrong value resistor...bad pot (audio probe each side of the pot > input, wiper, be sure other end is at 4.5ish volts).   Take the path that is simplest...audio probe the pot, the base and emitter of the transistor...is the 510k going to the base, other end to 4.5V?     Check emitter output - be sure all resistors/cap are installed properly. 

This is why tagboard debugging is more difficult....if you have sound at the IC, you WILL find the error, tho, with patience!

Don't worry about it, I really appreciate you taking time for this. I'll stick with it and post my findings. Thank you very much!