Tonepad Tubescreamer not working - No sound at all! Please help!

[Hav]

Hi all,

I've built a few circuits before, and have built the tubescreamer on veroboard successfully a while ago.

Had a go at tonepad's pcb (etched it myself - traces were perfect).

I seem to be getting no sound whatsoever when the pedal is engaged.

It is linked up to a working confirmed 'test box' that has my 3PDT, mono jacks in and out etc all wired up. THE TRUE BYPASS seems to work. I get a clean signal. When it is engaged, there is no volume whatsoever.

Its powered by 9v wall.

I have a worry that I have the transistors in the wrong way or the two 1uf's (which I used electrolytics for) are positioned the wrong way.

If anyone has any ideas on how I can debug this, please help - I've read through quite a few other forums but nothing seems to be the problems I may have here.

I can post IC voltages when home tonight if required.

TRANSISTORS are 2N5088s

LINK TO IMAGE OF BOARD: http://havsingh.com/photo.JPG

LINK TO TONEPAD'S PRODUCT: http://tonepad.com/project.asp?id=1

[GibsonGM]

Hi Hav,

Welcome!  Your problem isn't uncommon, and is usually something simple.  Why don't you go here, and do what it says? Then we can help you.
Do you have a DMM?

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[Hav]

Hi, thanks for the quick reply!

I do have a DMM, and thanks for that link, I will definitely go through those and post back here later tonight! I'm really hoping its something quite simple like the 1uf's pointing the wrong way or the transistors (I socketed them all because I knew it could be a problem!)

:-)

[duck_arse]

that green wire at the input isn't connected to ground, by any chance?

[Hav]

It does look awful close, but it wasn't that unfortunately!

Good spot though!

[Hav]

Right, here we go:


1.What does it do, not do, and sound like?
only works when true bypass is enabled. Absolutlely no sound when pedal is engaged.

2.Name of the circuit = Tonepad's Tubescreamer

3.Source of the circuit (URL of schematic or project) = http://tonepad.com/getFile.asp?id=81

4.Any modifications to the circuit? N

5.Any parts substitutions? If yes, list them. 47k instead of the 51k, 2N5088 Transistors, 2x 1uf ELECTROS - my biggest worry - orientation as these are polarized but the diagram doesn't show which way to position them...

6.Positive ground to negative ground conversion? N

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? =>no battery

Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = N/A
Voltage at the circuit board end of the black battery lead = N/A

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

WALL: 9.28

Q1
C =9.29
B =2.82
E =3.51

Q2
C= 9.29
B=2.82
E=3.53

IC1 (or U1)
P1: 4.59
P2: 4.76
P3: 4.55
p4: 0
p5: 4.58
p6: 4.59
p7: 4.59
p8: 9.29


D1
A (anode, the non-band end) = 4.76
K (cathode, the banded end) = 4.58

D2
A = 4.59
K = 4.79


Any help would be greatly appreciated, and will really help me learn how to debug too :-)

[LucifersTrip]

Shouldn't both QC's be 9V and the E's lower voltage than B's.  Flipped measurements or Q's?

[Hav]

sorry! I got the measurements the wrong way round. I have adjusted them above now to show what is it... 

[LucifersTrip]

still E's should be lower than B's, by around .5V  

Do you have the pinouts correct? flipped?

[Hav]

I am checking in reference to this which shows that if looking at the flat side of the transistor, the left most pin is the E : https://www.futurlec.com/Transistors/2N5088.shtml

According to this, I have them in correctly..  if this is a problem, what could be causing it?

[anchovie]

You need to trace this through with an audio probe and find the point in the circuit where the sound disappears.

[Hav]

ok, will have a go at that..

could anyone confirm that I have the 1uf's the right way round? I'mnot too sure how to work it out at the moment..

[Hav]

do any of the numbers above look out of place? apart from the transistors obviously (just tried new ones and its the same)

[GibsonGM]

Just make an audio probe (very simple - here:  http://www.diystompboxes.com/pedals/debug.html  )

Use it to follow the path from input, thru Q1, to input of opamp, output 1, input 2, etc.   At some point, your guitar signal will stop.   In that area is likely your problem.
For a circuit as simple as a TS, I think this is the best way to approach it, once you know you have power, etc.   Probably a solder bridge or something.

I doubt backwards electros will block signal entirely - they would probably fail later on, but not for quite a while at these low voltages.  If it IS the caps, you'll have signal right up to one side of them, and it will be dead on the other.

Unless you weren't able to update the voltages you posted, the emitter vs. base voltages on your Q's are still screwy...if this is the case, you have an issue there.   Emitter should be ~.5V lower than the base for an NPN transistor...mistaken pinout, short, etc., can cause this.



Audio probe!

[Ice-9]

Yeah as others have said use an audio probe until you find where the signal disappears then trouble shoot that area.

The electro cap polarities in this shouldn't stop the circuit from passing a signal if they are the wrong way around but may eventually get damaged.
I don't have access to the tonepad layout at the moment but in this circuit put the caps in the way the signal flows , ie input from guitar-follow the signal and place that cap with the + terminal first, then the - terminals flows to the first op amp section. The same for the other cap, follow the signal passing to the output so that when the signal goes into the cap, it flows into the + terminal and comes out at the - terminal.

[Hav]

Thank you so much for the replies! I will build an audio probe, find out whats going on and report back!

[duck_arse]

3 ways to go with the  2 NP electros:

- use polyester, forget about polarity probs
- use polyester temporary, tack-in any value you have, and measure the dc on each side. install an electro with positive to the higher voltage
- use NP caps.

you have in fact measured and posted the relavent voltages for the first one, at least. temporary poly caps will prove/disprove the workings, if not the full tonal qualities of the circuit.

[DrAlx]

For electro caps, the terminal marked as negative needs to have a smaller voltage applied to it than the positive.
So get you multimeter and measure the voltage between ground and that negative terminal of the cap (call that voltage 1).
Then measure the voltage between ground and the positive terminal of the cap (call that voltage 2).
If voltage 2 is less than voltage 1 then the cap is in the wrong way, regardless of what the schematic says or doesn't say.
It's not unknown for schematics to get things wrong.

You can use the above test on pretty much any circuit that you build.
In cases where a schematic is not clear about orientation, you should use those measurements to tell you which way to put the cap in.
I have put in electro caps the wrong way before.  The circuit still worked and the caps survived.  If your electro caps are in the wrong way then just take them out and put them in the correct way and don't worry about it. (The exception is tantalum caps.  If you put those in wrong you'll kill them)

Oh and those transistor readings look wrong.  The C looks OK at about 9V but the middle pin (B) should be about 0.6V bigger than the E pin as pointed out above.

[LucifersTrip]

I honestly don't see the real need for an audio probe yet if you have bad voltages at the first transistor, which is the first stage.

http://www.muzique.com/schem/ts808.gif

I really think sorting that out (still a measuring error?, bad/wrong component in surrounding area, solder bridge, still flipped?) is the first step.

Remember, there's the same bad voltages for Q3, so look for something where it's easy to make the same mistake twice.
Wrong pinouts is usually the #1 guess, but a wrong value resistor is also up there...

There's only a couple resistors on Q1/Q3 so it shouldn't be that difficult to figure out why the voltages are where they are.

[DrAlx]

It looks very suspicious that the B voltage is so low on both Qs.  I suspect that the "Vr" is bad.  (See LucifersTrip schematic for what I mean by Vr).
That "Vr" sets the bias voltage on both transistors and should be roughly half the supply (not 2.82 as you measured).
Looking at where that "Vr" comes from there is just a simple voltage divider (two 10k resistors between supply and ground)
and smoothing electro cap to ground.

Try this: Take out the electro smoothing cap on the voltage divider for Vr.
If there is some sort of short on that cap (because you put it in the wrong way and it burned through) then it will make Vr too low (which is what you seem to have)

Then measure Vr again.  It should be roughly half the supply.
If it is still not half the supply then recheck those two 10k resistors that produce the Vr voltage.
Make sure you have the correct  resistor values.
If you have, then check for shorts between the Vr line and the ground line.