Tube Screamer clone not working

[jcwillow777]

Hi:

I recently purchased a circuit board from www.generalguitargadgets.com. It was for the ITS8 - the Tube Screamer 808 clone. Info can be found at:

http://generalguitargadgets.com/index.php?option=content&task=view&id=90&Itemid=118

The bypass switch works and the LED lights up when the pedal is on, but there is no sound. I used steel wool before I started soldering. I did make a few mods. C4 calls for a 51pf capacitor but I didn't have one, so I used a 47pf cap. I also didn't use a stereo jack for the input, because I don't use batteries, only 9VDC jacks. I also did the AMZ fat modification as listed on page 3 of the Modification Instructions. Other than that, everything else is stock. I took several readings and this is what they are:

Drive    1 – 4.55V            Fat Switch    1 – 4.73V when on
   2 – 4.55V                  2 – 4.73V when on
   3 – 4.55V                  3 - NA

Tone    1 – 4.55V             Fat Switch    1 – 4.54V when off
   2 – 4.55V                  2 – 4.73V when off
   3 – 4.55V                  3 - NA

Level   1 – 4.53V
   2 – 3V
   3 – 3V

R1-8.3V   D1   C1-0V/8.31V   Q1   IC1
R2-8.3V/4.55V   A - 4.68V   C2-4.5V/8.32V   E - 8.31V   Pin1-4.58V
R3-8.3V/0V   K - 4.58V   C3-4.68V/4.54V   B - 8.31V   Pin2-4.68V
R4-4.49V   D2   C4-4.71V/4.56V   C - 9.03V   Pin3-4.5V
R5-4.49V/4.45V   A - 4.58V   C5-4.56V/0V   Q2   Pin4-0V
R6-4.55V   K - 4.68V   C6-NA   E - 8.31V   Pin5-4.57V
R7-4.57V/4.67V   D3 - 4.58V   C7-4.55V/0V   B - 8.31V   Pin6-4.58V
R8-4.57V   D3 is a jumper   C8-3.02V/4.56V   C - 9.03V   Pin7-4.58V
R9-9.02V/4.55V      C9-4.53V/0V      Pin8-9.03V
R10-4.55V/0V      C10-3.02V/8.31V      
R11-0V      C11-0V/7.57V      
R12-4.55V/8.31V      C12-9.02V0V      
R13-0V            
R14-8.31V/0V            
R15-8.31V/7.56V            
R16-4.57V/4.56V            
R17-4.58V            
R18-3.02V            
R22-0V            



 

[gaussmarkov]

it took a moment to figure out the original formatting of your readings.  nice thorough documentation there. 

there's something amiss with your transistors.  i suggest that you check their pin out and the way you have them connected.

best wishes, gm

[jcwillow777]

Thanks.

I didn't think this one went through. I should say, I wished this one didn't go through. I had everything laid out in Word. I cut and pasted and voila - total mess. I thought I deleted it. It is easier to decifer in another posting - ITS8 tube screamer not working. I pasted  it below.

Hi:

I am relatively new at building pedals. I have modified several pedals through Indygutarist.com. I have built a few A-B boxes, but I haven't had a lot of luck builing pedals. I am determined to figure this one out though. But,I need a liitle help!   I recently purchased a circuit board from generalguitargadgets.com for a tube screamer clone. The info can be found here:

http://generalguitargadgets.com/index.php?option=content&task=view&id=90&Itemid=118

The bypass switch is working. When I plug my guitar in and the pedal is in bypass mode I get sound throught the amp. When the pedal is on, the LED lights up but there is no sound.

I have done a few modifications. I changed C4 to a 47pf capinstead of the 51pf cap that is specified, simply because I sisn't have one. I also used a mon jack for teh input beacuse I don't use a battery, just a 9VDCS power. I added the AMZ Fat modifications as explained on page three of the modifications pages. Lastly, I put in an IC socket so I can switch out chips. I currently have an OPA2604AP chip installed now.

I have taken a few readings.

D1
A - 4.68V
K - 4.58V

D2
A - 4.58V
K - 4.68V

D3 - 4.58V (jumper)

Q1
E - 8.31V
B - 8.31V
C - 9.03V

Q2
E - 8.31V
B - 8.31V
C - 9.03V

IC1
Pin 1 - 4.58V
Pin 2 - 4.68V
Pin 3 - 4.5V
Pin 4 - 0
Pin 5 - 4.57V
Pin 6 - 4.58V
Pin 7 - 4.58V
Pin 8 - 9,03V

I have also taken readings at all of the capacitors and resistors, I will imput the info if you think that will be helpful. After looking at the instructions page, 3, I see that the readings on the transistors are high, I just don't know what I need to do to fix it.

I made an audio probe, care of R.G. Keen. I plan on using it tomorrow. I am a liitle unsure what to expect. I know that the 1/4" jack plugs into the amp and the shield is clipped to ground and I probe with the capacitor lead. I'm just not sure what I should or should not be hearing so as to know if there is a problem or if it is OK.

A picture of the pedal can be found here:

http://s137.photobucket.com/albums/q232/jcwillow777/ITS8/

Thanks in advance for any advice you can give me so I can get this baby up and running. 

[gaussmarkov]

well, it's good to have the resistor voltages too.  and the picture.  nice work.  it looks like you have the transistors
in correctly.  but their voltages are wrong.  the collectors are fine (contrary to what the ggg instructions say the collector
on Q1 should be your battery voltage).  from the instructions you can see that the base should be lower and about 0.5V above
the emitter.

what transistors are you using?  somehow your circuit is turning the 4.5V of Vr into the much higher value of 8.3V.
for example, R2 should be stepping that 4.5V down to an even lower value.  so even though the transistors seem to
be positioned correctly, it looks like there is still something wrong with the transistors.  could you be using a different
transistor than specified by the schematic?

[jcwillow777]

Thanks for responding - next time I won't make it so difficult. I used two 2SC1815 (original) low gain NPN biploar transistors. I got them from small bear.

http://www.smallbearelec.com/Detail.bok?no=298

Actually the number from small bear was 2SC1815-GR, I just assummed this was the same, but maybe not.

A little off subject, how do I post a picture directly into the post and not via photobucket? I just thought it would be less steps for people to take in helping me.

Thanks again

[R.G.]

Your transistors are way off.

This is possibly because the 2SC1815 is a different pinout than the boards need. Most TO-92 2Nxxxx types are EBC looking at the flat face with the pins down. The 2SC.... series are ECB. Check that against your board and see if that is the problem.

[jcwillow777]

Your transistors are way off.

This is possibly because the 2SC1815 is a different pinout than the boards need. Most TO-92 2Nxxxx types are EBC looking at the flat face with the pins down. The 2SC.... series are ECB. Check that against your board and see if that is the problem.

I checked mouser and saw a pin out for the 2SC1815, it showed CBE, so I turned the transistors around. I never thought of that. Thanks. But alas, no sound.

Q1
C - 8.81V
B - 2.9V
E - .39V

Q2
C - 8.9V
B - 2.9V
E - .36V

I am starting to go through the pedal with an audio probe. I found a possible problem a R22. The end of the resistor coming from or going to the input jack I have sound, but no sound from the other end of the resistor that goes to ground. Would that be normal?

Thanks again.

[jcwillow777]

I'm using the audio probe and I have gone successfully to R2. The side of the R2 that hooks up to R1 has sound, but the side of the R2 that hooks up to R6 has nothing. I resoldered the connection 3 times but nothing seems to change. I checked the resistor and it seems to check out OK. The layout calls for a 510K resistor and the MM shows 506K. Not sure where to go from here. I have sound at the base of Q1, but not from E or C.
Thanks in advance

[gaussmarkov]

Your transistors are way off.

This is possibly because the 2SC1815 is a different pinout than the boards need. Most TO-92 2Nxxxx types are EBC looking at the flat face with the pins down. The 2SC.... series are ECB. Check that against your board and see if that is the problem.

I checked mouser and saw a pin out for the 2SC1815, it showed CBE, so I turned the transistors around. I never thought of that. Thanks. But alas, no sound.

Q1
C - 8.81V
B - 2.9V
E - .39V

Q2
C - 8.9V
B - 2.9V
E - .36V

I am starting to go through the pedal with an audio probe. I found a possible problem a R22. The end of the resistor coming from or going to the input jack I have sound, but no sound from the other end of the resistor that goes to ground. Would that be normal?

Thanks again.

your transistor voltages still do not look right.  there should be a .5V-.6V difference between B and E.  according to R.G. and the datasheets that i just checked, the collector is the middle pin of your transistors.  so turning them around won't do the trick. 

you need to rearrange the order the leads attach to the board.  the ggg layout as the pads labelled.  with the flat side facing to the left, the connections are EBC from top to bottom.  the datasheets say that the order of your pins is BCE when facing the same direction.  so turn yours around to get the emitter at the top and then switch the order of the two leads toward the bottom.

[jcwillow777]

I switched the pins like you suggested.

Q1
E - 0
B - 2.91
C - 8.81

Q2
E - 0
B - 2.91
C - 8.81

Voltages are still way off. He gave several options for transistors, I think I might just go to Radio Shack and try to get some different ones.

[jcwillow777]

I went to radio shack and I got some different transistors. I got some 2N3904 NPNs.

Q1
E - .92V
B - 1.48V
C - 8.81

Q2
E - .69V
B - 1.24V
C - 8.81V

The voltage is still not what GGG shows that it should be they show:

Q1
E - 0v
B - 3V
C - 3.5V

Q2
E - 3V
B - 3.5V
C - 9V

The 2N3904 show the direct opposite pin out that the picture on the layout, so I turned the transistor around. Still no sound.

[Unclerny]

Let me give it a shot. 

I'd use your probe on the left or output of each component DIRECTLY in the signal path and see where it stops.  Okay, you have signal at Base of Q1, check the Emitter for signal.  Then go to Pin 3 IC 1, then pin 1, Pin 5, Pin7, base of Q2 and emitter of Q2.

Where the signal stops is after the problem.

I know that the biggest problems are wiring, open connections, and wrongly oriented components.

Good luck  UE

[jcwillow777]

OK - 1 step forward, ten steps back. I changed the transistors and now the sound has stopped at C1. I have the sound going into the cap, but not coming out. Is it possible that the cap is bad? I have resoldered the connection, twice, and R2 after C1. The sound is no longer making it to B of Q1.

[Izzy]

It would be very helpful if you post the schematic that you are refering too.

[jcwillow777]

It would be very helpful if you post the schematic that you are refering too.

The schematic is here:

http://www.generalguitargadgets.com/pdf/ggg_its8_sc.pdf

The layout is here:

http://www.generalguitargadgets.com/pdf/ggg_its8_lo.pdf

Thanks

[Izzy]

You will definately hear the signal before C1, coz its the first step.
To me it sounds like you have a short circuit somewhere in the signal that why the signal aint going that way.
I might be be wrong.

[64fx]

Sorry to revive such an old thread, but hopefully someone can help me out.  I'm having basically the same problem.

I too have the GGG ITS8.  I purchased the board and got my own parts from Small Bear.  After reading the thread I realized that I didn't have the transistors (2SC1815) in correctly, so I swapped them around, but still get nothing.  When the switch is bypassed I get sound, but when it's engaged I get no sound or LED.

I did the "Very Expensive Boutique Mods" to it with the asymmetrical diode clipping.

Here's the link to it:
http://www.generalguitargadgets.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=22&category_id=7&option=com_virtuemart&Itemid=45

Below are the voltage readings I got:

Q1:
C=8.81
B=3.84
E=.1

Q2:
C=8.8
B=4.14
E=0

IC:
1=4.4
2=4.45
3=4.39
4=.1
5=4.39
6=5.32
7=4.55
8=8.8

A friend of mine is helping me build this pedal, and we both double-checked everything.  All grounds seem right, the 3PDT switch is wired up according to the layout from GGG.

I'm stumped.

Any ideas?

Thanks!
Daniel

[Brymus]

IF the 3PDT swicth is wired up right and you used a dropping resistor(around 4k7) on your LED it should light up when engaged.
Thats its job to show you when the circuit is switched on.

[MikeH]

You might have your switch oriented wrong.  If the poles connect from top to bottom:

-  -  -
-  -  -
-  -  -

is correct.

l  l  l
l  l  l
l  l  l

is not correct.

hope that makes sense.

[The French connection]

Is pin4 should'nt be 0V? Check around that and get your audio probes ready!

Dan