My Tube Screamer has no distortion

[maroonedwizard]

Hi . I have just finished my tube screamer clone based on the schematic from tonepad  http://www.tonepad.com/getFile.asp?id=81 and the problem here is that there is no distortion at all. Only clean sound and the drive pot acts like additional volume. I have done no modifications and i have connect the negative of the tantalum caps to the ground. All parts are exactly as listed and there are no sortcircuit or missing ground anywhere.

i have measured the volts on the opamp an the transistors

Q1
C =9
B =0.02
E =0.62

Q2
C=9
B=0.02
E=0.62

IC1 (or U1)
P1=4.2
P2=0.12
P3=0.26
P4=0
P5=1.36
P6=2.61
P7=4.2
P8=9

I try to make it work for 3 days now and i haven't done anything............. please help!!!!!!!

[oskar]

Check Vb... It should be 4.5V

[Plinky]

Transistors (as well as the IC) are way off. Are you sure there isn't a solder bridge somewhere? What kind of transistors are you using and are you sure the orientation is correct?

[maroonedwizard]

The transistors are 2N3904 and they are oriented the right way . Concerning Vb=0.60  and im trying to figure out why because there is no solder bridge somewhere .

[the_random_hero]

Are all your Vb points connected to Vb from the battery? You should be getting 4.5V at B of Q1, Q2, etc. What interests me is that you're getting 4.2V at Pin 1 of IC1, which is suggesting that at least that point is connected to Vb.

[maroonedwizard]

The positive of the battery connects to the C's of the transistors , the pin 8 of the IC and the 10k resistor . On one side of the resistor i've got 9V and on the other side i've got 0.60V . I have triple check everything and the problem remains . Its drives me crazy 

[brett]

Hi.
Logic and experimentation.  They'll always get you there.  (For technical issues, at least).

The easy, proximal answer is that the voltage divider isn't doing it's job. The difficult, ultimate question is "why not?".
First, check that the 10k "upper" half of the divider is actually 10k. 
IF that's correct, then the fault is in the "lower" half. The resistance must be much less than 10k.
Check the value of the resistor (by colour, or by taking one end out...the meter may well measure another resistance path)
If the resistor is ok, then check the orientation of the smoothing cap for Vb.  If it is in the right way around, disconnect it.  (Reconnect it if nothing improves)
Next, pull the IC out of the socket. (I hope you used a socket.  They are very handy for just this situation).  Did Vb rise to 4.5V with no IC?  Then it's the IC.
Otherwise, you'll need to disconnect each of the other Vb connections until you strike gold.

That's all I can think of.  (I'm working from memory, so there might be something else, somewhere, but you've probably got the general picture.)
cheers

[maroonedwizard]

Hi.
Logic and experimentation.  They'll always get you there.  (For technical issues, at least).

The easy, proximal answer is that the voltage divider isn't doing it's job. The difficult, ultimate question is "why not?".
First, check that the 10k "upper" half of the divider is actually 10k. 
IF that's correct, then the fault is in the "lower" half. The resistance must be much less than 10k.
Check the value of the resistor (by colour, or by taking one end out...the meter may well measure another resistance path)
If the resistor is ok, then check the orientation of the smoothing cap for Vb.  If it is in the right way around, disconnect it.  (Reconnect it if nothing improves)
Next, pull the IC out of the socket. (I hope you used a socket.  They are very handy for just this situation).  Did Vb rise to 4.5V with no IC?  Then it's the IC.
Otherwise, you'll need to disconnect each of the other Vb connections until you strike gold.

That's all I can think of.  (I'm working from memory, so there might be something else, somewhere, but you've probably got the general picture.)
cheers

I have done as you said and notning happens. But when i connect back all the resistors somehow it worked . I have know distortion and all the functions of the pots but when i measure again the volts : 

Q1
C =9
B =0.02
E =1.62

Q2
C=9
B=0.02
E=1.62

IC1 (or U1)
P1=4.2
P2=4.13
P3=0.50
P4=0
P5=1.36
P6=2.61
P7=4.2
P8=9

So is this ok ? I haven't heard before a Tube screamer by its own so i cant tell if it working the right way.

[wampcat1]

You have something funky going on there with pin 3 - you should have higher voltage than that.
bw

[maroonedwizard]

Im tired trying to make it right . I will call it booster and im going to built the tube from the start . Thanks a lot guys for your help.

[wampcat1]

Im tired trying to make it right . I will call it booster and im going to built the tube from the start . Thanks a lot guys for your help.

With all respect, knowledge either costs money or time. It will take time to learn this stuff and troubleshooting is one of the best methods of learning.
You need to retrace the circuit one piece at a time while looking at the schematic, checking connections, joints, voltages, etc. Pin 3 of the opamp needs to go to a resistor (10k IIRC) that leads to 4.5v. SO, you would have somewhere in that neighborhood if it was working correctly. With that piece of info, you need to figure out WHY you don't have the voltage there... is the 10k resistor there? If so, what is the voltage on both sides? If voltage is good on both sides, why is voltage not getting to pin 3? resolder joints. If still no voltage, replace resistor. If STILL no voltage then backtrack even further... replace IC and check. Replace transistor buffer and check...etc.

See my point? It's all about troubleshooting and learning. After a while, you'll get the hang of it and debugging goes MUCH faster.

Hope that helps!

bw

[Roobin]

Hey there,

Those transistors have something odd going on there - the base is below the emitter. If I remember correctly, the base needs to be about 0.7v above the emitter to work properly. See http://www.diystompboxes.com/wiki/index.php?title=Debugging, scroll down a bit.  So your transistors may be connected incorrectly. I had some problems with 2n3904s or bs170 (can't remember which) a while back and it turned out to be the pinouts I saw on the net were wrong when checked against the company datasheet. So try reversing them ( hope you have a load left!).

Before you give up have a look at this - https://www.generalguitargadgets.com/pdf/ggg_its8_instruct.pdf - more specifically page 3. Then go from there. Go through every solder joint with a magnifying glass and copy of the schematic/layout, highlighting as you go. It worked really well for me.

[maroonedwizard]

Thanks for all the support . Im sitting above the TS circuit for 4 days now and trying to troubleshoot it.  I have build 3 more TS and some other pedals in the past and all had worked almost right away or i made them work eventually. I have tried all the known "methods" of troubleshooting and have un- and resolder almost anything twice . Im not a pedal guru but from my little experience i find this thing, Vb=0.6 no mater what , pretty weird . Maybe the bassist cursed me because i haven't build yet that octaver . Anyway i m going build another one sometime this month but right now i dont have much spare time . Thanks again.

[R.G.]

Gentlemen, whenever you see a voltage of about 0.6V, what should you think?

Right - forward biased silicon junction.

It may not turn out to be that, but a lot of times it is. Enough times to make suspecting that automatic.

Doctors have a saying: "When you hear hoofbeats in the hallway, don't suspect zebras." meaning of course to suspect the obvious things first, not the rare ones.

[maroonedwizard]

Gentlemen, whenever you see a voltage of about 0.6V, what should you think?

Right - forward biased silicon junction.

It may not turn out to be that, but a lot of times it is. Enough times to make suspecting that automatic.

Doctors have a saying: "When you hear hoofbeats in the hallway, don't suspect zebras." meaning of course to suspect the obvious things first, not the rare ones.

Sorry to ask but what exactly "forward biased silicon junction" mean ? I don't understand all the electrical terms in English

[petemoore]

  'diodes backwards from the schematic [would be the translate to your problems solution if that's it].
  Good eye RG. Could be the reverse polarity diode is reverse polarized, it's foreward threshold voltage is about .6v, [forward biased silicon junction. ]anything below that it doesn't 'see', anything above that it clamps.
  >The line on the diode goes towards V+.
  as long as you don't reverse polarize the circuit PS, you can pull the diode and try, or try testing the diode with the DMM, use a diode to see what the readings look like on a good diode [test both directions].
  It's maybe just needing turned around though.

[maroonedwizard]

I checked the diodes , and replace them even they looked ok but nothing happen.

[brett]

Hi
my 2c says that your transistor orientation is wrong.  The evidence is that you are getting voltages on the "emitters" of NPN devices when there's no base voltage.  They aren't supposed to be conducting, but they are.  Maybe they're PNP?

What type are they? 2N5088/2N3094s and some others are E-B-C looking at the flat face with legs down.  BC549C and others are C-B-E.

[maroonedwizard]

I m using 2N3904. Im pretty sure about the orientation and i have tried and some 2N3904 from different companies. And another thing , last night i was checking for grounds and found at the 47uf (down left corner of the schematic ) when the battery was connected to the circuit the cap lets current to pass to the ground . Is this normal ?

[R.G.]

No. It's backwards.