ROG Thunderbird - unbearable noise:(

[bsas]

Hi all,

I just finished the ROG Thunderbird PCB (1776) build and something is weird.

The pedal is working and sounds amazing, but, it is unusable because of the noise. I thought it was going to go away after I box it but it didn't, at all.

Don't know what it can be. I can post an audio clip with the noise and pics of the pedal if that helps.

p.s.: I notice that it is just the "level" knob.

Thanks!

[bsas]

News: something is odd with my ground and maybe I am having some DC leaking, because all IC pins that suppose to measure 0V they have 1.2mV. also I can see this 1.2mV difference between the power ground and the circuit ground :(

[Frank_NH]

I've built the 1776 PCB.  First, the Thunderbird is a somewhat "noisy" circuit due to the many gain stages the signal passes through.  Any noise at the input gets amplified.  Use shielded wire for off-board signal connections (input and output jacks).  Second, if the ground is not 0V, check your off-board wiring.  If there is some DC leakage, it could be one of your capacitors.  Check the orientation of all of your electrolytics and tantalums.  If it's a bad capacitor, that may be more difficult to diagnose short of removing each one and measuring.

Schematic here:

http://www.runoffgroove.com/thunderbird.html

[bsas]

For my offboard wiring I used the "diyguitarpedals" 3pdt delux PCB (far easier/faster to do then manually).

Already triple checked the capacitor polarities, and all are correct.

How do you suggest me to "debug" the offboard wiring? Is there any thing I should look for, maybe as a "sign" of a bad 3pdt switch?

Here is the sound (just pedal to amp, no guitar, just changing the "level"):
http://tinyurl.com/nwak4vy

And here is the pedal image:
http://tinyurl.com/q9gbmv6

[bsas]

Maybe I found something.

In the 1776 docs, they specify the voltage on the ICs.
Two pins in my voltage doubler IC are very out:

Pin 6: 4.14V (expected 2.54)
Pin 7: 5.30V (expected 1.42)

Do you guys have any idea what could be causing that? Any specific capacitor or diode (or even the transistor)?

Thanks!

[bsas]

Oops, my bad.

Just notice that those pins are not connected to nothing, therefore doesn't make any difference and the voltage difference is probably because I am using a 1044 IC instead if the recommended LT1054 (I order one but it is taking forever to arrive so I am using the 1044 for now).

Now I am lost. Don't know what to look for. Or maybe this pedal is noisy... :(

[Frank_NH]

You may want to wait for your LT1054.  While you can often substitute a LT1054 for a 1044, the reverse is not necessarily true.  The power section of the circuit it rather complex and I would avoid using anything other than the LT1054 for the charge pump.