Trouble with ITS8

[jwade]

Hey everyone,

I just completed my first build (General Guitar Gadgets Tubescreamer Clone). When I went to test the pedal there was no sound. I plugged the guitar directly into the amp and it worked normally. I hook up the pedal and there is no sound when the pedal is not turned on, and a faint sound when it is. The LED lights up, and all the voltages on the IC are correct so I am totally in the dark as to what could be wrong. If anyone could provide some insight into this before I lose my mind it would be greatly appreciated.

[jkokura]

I have the same problem, will be debuggin mine tomorrow.

Usual suspects are: Cold solder joints, wrong parts, backwards parts, bad wiring, or a faulty part. Use the debugging thread to give use more details and we'll be able to help you... http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Jacob

[jwade]

Found my problem. The tongue on the input jack was touching the pot. I rotated the jack about 30 degrees and it works great now.

[stuznu]

Hi all,

Newbie on this site, so many interesting projects and so little time.
I have made a start building an ITS8. I have it all complete, assembled and connected to a 9v powersupply. I am reluctant to instal into case until all tests are completed.
When I activate the bypass switch the red LED lights up.
Tests using DVM indicate the existence of a problem as the voltages are not corresponding with test list provided by GGG.

Test points and voltages are listed below:
Q1:
C=5.75v
B=6.17v
E=8.99v

Q2:
C=5.95v
B=6.3v
E=8.99v

IC/Opamp:
P1=8.15v
P2=8.11v
P3=8.16V
P4=0.0v
P5=8.15v
P6=8.15v
P7=8.15v
P8=8.15v
( I have tried replacing the opamp - no change.)

D1 A (anode-non-band end) =7.9v
     B (cathode/banded end)=8.5v

D2
    A=8.15v
     B=7.9v

Capacitor test:
C1=6.18v
C2=8.16v
C3=8.14v both legs
C4=8.15v both legs
C5=8.17v
C7=8.5v
C8=8.15v
C9=8.95v
C10=8.15v (+v leg) , 6.31v (-ve leg)
C11=5.83v
C12=8.9v

I removed D1 and D2 and they test good.

Any advice and direction will be appreciated.

Thank you.

[Pojo]

Definitely an issue with those voltages. Could be an error with the bias reference. I'd start with making sure R9 and R10 are the correct value 10k resistors and also measure the voltage at the junction of R9 and R10...should be about 4.5V which is also the same voltage you should be getting at pins 1,2,3,5,6, and 7. The transistors also use that bias reference so that seems to reinforce my assumption at there's an issue at R9 and R10.

[stuznu]

Hi Pojo,

This has to be the quickest troubleshooting experience I have ever had! Found the R9 to be 0.99k instead of 10k. All voltages on opamp are good!

Checked Q1 and Q2 - all seems good. Will do more tests tomorrow. 1.30am here.

Thanks mate!

[Pojo]

Awesome..glad to help!

[stuznu]

Installed ITS8 into a case - and tested again. The tone pot doesn't seem to making much difference when adjusted. Checked wiring and soldered joints and all seems good.

[Kipper4]

I had a recent similar experiance and it turned out to be a bad resistor in the tone stack. Just saying

[stuznu]

Are able to specify which resistor? When you say 'tone stack' are you referring to the section of the pcb that contains components that adjust tone?
I will have to trace back from the Tone Pot wires to pcb tracks and check the resistors.
Any further information will be appreciated.
Will keep you posted.

[Kipper4]

mine had a bad R11
That's right the tone stack is made up of componants that alter the tone.

[stuznu]

I removed R11, R13 and R14 and tested using DVM all seem to be within spec. I also checked each of the wires from the pot to pcb - connectivity between pot and pcb OK.

BTW - R11 has 220E; what does the E stand for?

[Kipper4]

im certain form memory its a 220 Ohm resistor also refered to as 220R (C11)

did you test the pot too?

In fact i'd check all connections and componants around that op amp?
http://www.generalguitargadgets.com/pdf/ggg_its8_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a