TS808, lower output than input!?

[sebarb]

Hi all, I build TS808 clone from UK store, it sound well but
I need work with level pot at max or i loose some nuance in my sound.
When I use it as boost, maximum level and minimum gain, i loose a little bit of volume than with the stompboxe turned off!
With my multimeter from input and output jack, less 25% voltage output. Less output voltage than input, is it normal??

I don`t have electronic knowledge, so I hope some help to find a way,
Any one know which circuit section or component can be involved?
A good link to learn how test my circuit with multimeter?
Maybe there is a table with voltage check point onTS808?

Best regard

[GibsonGM]

Check all of the resistors around the opamp IC's.  Also check that your gain and volume controls are connected properly!

You will need to measure the voltage at each IC pin, CAREFULLY (don't short the pins together!! One at a time...).

Connect black "-" probe to the battery "-".   Use the red + probe to measure and record the results.   Make sure the meter is set to DC volts.

This is not a terrible problem, since you can hear the pedal.  It works, it just has a minor problem that we'll help you find. 

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

[sebarb]

Thank for you quick answer and guidance GibsonGM.
It`s TS808 from pedalpart UK, build with symetric diode clipping and I replace the 51k resistor R7 on the drive pot pin 3 by 22K (more/less drive mod)
And add an JRC 4558D.

               Battery voltage  8,81v
ground circuit to battery +  8,43v
ground circuit to battery -   0

          IC JRC4558D pin 1  4,25v        pin 8  8,49v
                                   2  4,29v             7  4,23v
                                   3  4,24v             6  4,24v
                                   4  0                   5  4,24v

                              Q1  E  3,11v      Q2  E  3,13v
                                    B  3,57v            B  3,59v
                                    C  8,42v            C  8,41v

                              D1  A  4,2v        D2  A  4,16v
                                    K  4,16v            K  4,2v
     
                                 Z1 A 0v
                                     K  8,32v

Every polarized Capacitors and condensators show positive pin beetwen 4v to 8v and negative pin at 0v,
same for the unpolarized Capacitors 1 pin beetwen 4v to 8v and 0v for pin 2.

http://pedalparts.co.uk/docs/ToobScreamer.pdf

Regard

[GibsonGM]

Do you have the switch wired in yet?

Does the tone control do anything?
Are you SURE that you put the right value pot in the right place??   ESPECIALLY the one for "Drive", which MUST be 500K.   Check the pots!!

Are you sure that Q1 and Q2 did not get put in "upside down"?  I mean rotated so that the collector is where the emitter should go.   That would go far in explaining your problem.  The voltages are *ok*, but not *ideal* for base > collector voltage, should be more like .7V.


Do you know how to make and use an audio probe?   http://www.diystompboxes.com/pedals/debug.html  If the above does not work, I would "listen" to the IC pins 3, 1, and then 5, 7 and see if you notice the signal getting quieter than input in any spot.   You should have a boost at 1 and 7.     See if this works, for starters...

[sebarb]

HI all, thank again GibsonGM, this audio probe is a perfect tool!

_ Yes the switch wired
_ The tone control work well, (but its not big range)
_ All pots get the right values, right place and solder and action
_ Q1, Q2 are also in the right side

Audio Probe on IC

      pin 1,2,3,  louder than input, (trebly)
      pin 5,6,7,  louder than input, (bassy)

      pin 1, are louder, yes real boost
      pin 7, i am not sure, no realy, maybe.. a little!

      pin 4 and 8, nothing

i don`t know about the no boost on gate 7 but when i followed the signal with the audio probe, the signal sound realy good on the level pot confront the imput and output jack but
after that, the signal start to decrease.

level pot is ok real boost
C10  ok
R12  little bit less signal and just one pin sound
Q2   little bit less signal
R14  not sure and just one pin sound
R15  not sure
C11  nothing change
R13  a lot less on the last

So, no real boost on IC pin 7 and slow signal decrease in the output buffer.
I have no ID except the easy way, leave off the output buffer!
but i realy prefer, find, understand, learn

Thank by advance

[GibsonGM]

OK!  If I am not mistaken, you have loud signal at the Level pot??    Listen to the signal at the side of R18 that goes to the Level pot.

If it is loud there,  the problem is with the pot, or after it....check signal at C10/R12.  Then at R15/C11.

You MUST have a capacitor in your audio probe to do this, or the DC in the transistor will make problems for you.  No capacitor in your probe = buzzing and clicks that don't mean anything useful to us.   Just about ANY capacitor rated over your supply of 9V will do.

If you have good signal at the Level pot, the problem is after it, probably in the Q2 output buffer.  You would check every connection in there for cold solder joints, wrong value parts and so on.

If the problem shows up with low output at pin 7, your problem is likely in the tone control - and you would do the same thing, check all connections and values.

It is easy to make a soldering mistake!   Sometimes poking parts with the eraser on a pencil with the effect on helps to find bad connections.

[sebarb]

Hi all, a bit late, I had work outside!
No buzz on my audioprobe, there is a capacitor above.

The sonore level decrease with each components in the output buffer.
I checked every solder joints, I heated some, checked every components values, pots, wires, again and again,
switch with new IC, switch with new 2n3904 because the sound was a bit dirty on pin E Q2 and nothing change!

I shunted the ouput buffer to try and now it sounds like TS, realy transparent  and a now little highest ouput than input with level pot at max and gain pot at minimum.

So sure there is fews little trouble, inside and outside output buffer but i'm lost

[GibsonGM]

1) Are you SURE the transistor is in correctly?  It may be reversed, which will make it 'less loud'...

2) Your problem is somewhere between the Level control and R13. Check EACH connection!   If the connections are OK, and you have no good sound at the Emitter of Q2, then I think that transistor is dead.   Audio probe at R15, but make sure your probe has a capacitor attached to it.  A big one, like 1uF or 10uF, etc, is fine.  So is smaller, like .22uF.     Smaller just means it will sound more treble. 

3) what is the voltage on Pin 1 of your Level control?  It must be the same a "Vr".   Check R12 to see if it has the same voltage there, on its right side.  Post back.

It will take patience, but you will fix this

[sebarb]

1) yes Q2 is in right position

2) Q2 is not dead,  i tryed 3 new transistor for Q2 for the same result

3) Battery 8.45v
Pin1 level pot 4.1v
R12  4.1v and 3.18 in other side
Ic pin1 4.10v
Vr feeback loop 4.1v

With the audio probe i didn't find  big drop in the level, just little bit on each components along the output buffer!

Louder at feedback loop exit than ic pin 7 ? Pin 5-6 and 7 same level??

Regard

[GibsonGM]

Check R17 through the tone pot, C9 to R11 >> ground.   These feedback components set the level for the second amplifier on the IC...you should have SOME increase in level, I believe.   Check that your tone pot is wired correctly, no shorts, things like that...you may have a problem in that area.

Is the 'feedback loop exit' pin 1?  The output of the first stage?

[sebarb]

I see nothing bad around the tone pot, solders, wires!
R17 and pin 1 & 3 on tone pot sound good at same level, (highest than input and lowest than IC pin 1)
Tone pot pin 2 is lowest than pin 1 and 3
C9 and R11 sound same as tone pot pin 2 (Nothing in R11 ground side)

And about the feedbak loop yes feedbak loop output, exit C4 on the way to IC pin 1 a lot highest than IC pin 7 and the first stage is also highest than IC pin 7

[sebarb]

Problem solved,
I didn'd find what's wrong so I made home made circuit board, use the same component and recover all the original TS output!
So maybe a track on the circuit board to much heated by the 45w iron soldering used on this realization.

Thank for all your replys

[GibsonGM]

Problem solved,
I didn'd find what's wrong so I made home made circuit board, use the same component and recover all the original TS output!
So maybe a track on the circuit board to much heated by the 45w iron soldering used on this realization.

Thank for all your replys

You're welcome, sebarb.   Most often the problem is something like that, an easily over-looked thing.  I'm glad it works!