Distortion in a Presonus blender

[Treeline]

Just happened last night and I haven't encountered it before.

I have a Presonus AcoustiQ blender / tube pramp (wall wart grade) for acoustic guitar that has been pretty good so far. A few days ago I took delivery of a footswitch (designed for this unit) that lets me mute or go to a boost circuit with its own gain control. It tested out OK, and both standard and high gain circuits sounded fine through headphones.

Last night I was running sound at an event and tried to use it, but got some pretty serious distortion. I thought it was the guitar until I substituted guitars and had the same problem. I was distracted enough so I didn't pull the footswitch at the time to see if that was creating a problem, but the unit was not usable and I ended up running a passive DI to the board (a $25.00 Carvin junkbox saves my butt yet again...).

I plan to rule out as much as I can (such as a bad channel strip) when I get a moment to test it with the PA, but right now I'm scratching my head and I think it's the preamp.

This scenario familiar to anyone?

[Big Kenny]

change the tube(sovtek 12ax7 or jj ecc83) and remember not to overdrive the preamp volume/blend (first control). get the tone you want and add volume from the master

[Treeline]

Thanks. I ran it through its paces today and changing the tube is the next thing on the list. I'm a tube newbie...

[darrin_h2000]

go to ebay and score a NOS Mullard. 12ax7 much better than the SOVTEC