Am i gatting dc on my guitar volume pot from tw express pre

[zambo]

When I plug into this preamp my guitar gets the scratchy volume pot, which I hear can be caused by dc current? How can I fix this? I built the trainwreck express preamp as a stand alone unit to plug into variouse power amps... I would love any advice or help please. Thanks in advance!

[rooster]

OK, will state the obvious. V1 needs to be a good example, the cap at V1 (the first stage) needs to be a good example, and finally the pot in your gtr needs to be a good example, too.

Don't take any of these things for granted, that's all I got.

[funkmeblue]

I have experienced this with some examples of preamp tubes. Have you tried another 12ax7 in v1?

[zambo]

There is no input cap on v1 according to the schematic so I am not sure what you are refereing to. I want to understand, honest! Btw, Why is there no input cap or resistor on v1 ( besides the 1m to ground ) ? When I put a cap in line to v1 it stopped all sound from getting through. Anyone else have thoughts on this?

[zambo]

we must have been typing at the same time! I tried it with different tubes and also the same circuite, different build...I made two. same problem. Checked the guitar...different guitar..same problem.

[fishy]

What voltages are you running. You might be overloading the input grid. Some have seen this using VVR when the voltages get low. A cap in line sorts this out.
Maybe worth looking at that.

[zambo]

that seemed to sort it right out! Thanks! I tried that in my initial build but i guess a had a bad cap maybe. Oh I am currently running it at 9 volts. Not to much gain but makes for a good blues preamp. 12au7's sound great in it. Thanks again for the help. Greg