Distortion Problems

[skypn]

Consider this schematic:



When I run a 125hz signal from my computer through the pedal and output it to my computer speakers, it sounds oh so wonderfully dirty, yet sweet . Pot 1 gives it a great range of "dirts". Pot 2 doesn't add so much volume, as it adds flavor.
But when I run a six sting through it, still through the computer speakers, whenever I turn POT1 up pass 10:30ish, it starts to squeal. Pot 2 does little but change the squeal's threshold. Before that, it still sounds cool. If I had to guess, I would take a stab in the dark and guess maybe to play around with the values of POT1, and C2. or swap transistors, maybe.
What do you guys think are the usaul suspects?
TIA

[Aleph Null]

Can you take a picture of the actual layout? It might be an artifact of the breadboard or something.

[Aentons]

Just a guess, but it sounds like the computer is a high impedance output and the guitar signal is low impedance. You might try loading the circuit input with a 1M resistor to ground.