General Guitar Gadgets ITS8

[bmcash]

Hi guys,

I have a quick question concerning a GGG tubescreamer kit with the "expensive boutique mods."  I put together the kit and I get a by-pass signal, the LED works, and the pedals "kinda" works when engaged.  When the pedal is turned on, it sounds more like a fuzz face with limited gain.  I have tried different chips and it is pretty much the same result.  Also, the IC pin values are nearly double to what they should be!  IC pin 4 is supposed to read 0, but still measures about 6.5.  I re-wired everything, checked components, checked orientation, looked for solder bridges and tested continuity and everything passes.  Anyone have ideas? Faulty component? One thing about this pedal is that you have clipping options between LEDs and diodes and when switching between the two, there is definately a volume increase, but it still sounds like a fuzz no matter which clipping option.  There is a 1 meg drive pot installed, but there is not nearly any gain on tap.

Any comments or suggestions would be greatly appreciated and thanks in advance for looking.

Cash

[sgmezei]

Can you post any pictures? I have built 5 of these babies and they sound awesome. Not fuzzy, and a wide range of gain. Have you checked the orientation of your transistors?

[bmcash]

Hey man.  I checked the orientation of the transistors and they are correct.  However, when I checked their values, they were off.  Bear in mind this was before the complete re-wire and I do not have fresh values for them. 

I PM'd you about the pics.  The files were too large.

Thanks man.

B$

[jkokura]

As soon as I read you have 6.5 on pin 4 that indicates you have a solder bridge somewhere on there. Pin 4 should be 0V.

Jacob

[bmcash]

Ok.  I will check again.  I will trace pin 4 and see if i can find anything.

Thanks

[jkokura]

PM'd back Brandon.

Jacob

[bmcash]

Here is some more information.  My 9V battery is running at 6.22V and the IC pins ALL measure this value...even pin 4.  Furthermore, the ground on the pcb measure 6.22V.   I cannot find a solder bridge anywhere.   

[jkokura]

First off, trying to run a pedal at 6.22V is a big problem. Unlike a car which can run down to empty, batteries are actually no good when they fall much below 8V. You can run them with less sometimes, but most of the time they're dead. Get a fresh battery.

Second, you need to sort out why and how your power is leaking to ground. On your IC you should have about 9V on pin 8, about 4.5V on pins 1-3 and 5-7, and on pin 4 you should have 0. There is obviously big problems for that to not be the case.

Have you read the "rules for getting tech help" thread? Perhaps you should check that over and see if there's anything you can learn there.

Jacob

[bmcash]

Thanks for the input.  I am going to go back thru the circuit and try to find a leak to the ground.  This has to be the problem.  And i will get a fresh battery.

[sgmezei]

Sorry I was out of town this weekend and didn't write sooner.

Have you tried socketing the transistors and swapping out different tranny's and an IC?

Is pin two of the volume pot touching the case? Might just be the photo.

[bmcash]

I went ahead and orderes a new board and components with thwir second chance program.  I will be even mor careful this.time around.  I will probably build it this.weekend and share the results....good or bad.

[sgmezei]

geez I am sorry to hear that man.

Good news is it is easier to debug when you have a working one on hand. And at the end, you will have TWO!

[bmcash]

Got my second chance board in today and put it together in about 3 hrs.  It worked the first time I fired it up!  It sounds dang good!!  I need to fix the lead dress and make it more pretty, but that's about it!  I still do not know why the other board quit working.

Thanks for the help guys!

[sgmezei]

Thats good to hear man. Use the working board to check the dead one. You can check voltages and more importantly where you hear signal. The audio probe is your best friend!