The potentiometers are probably dirty and need to be sprayed and worked with some tuner spray. That is a common problem with those units.
As for the turn-on distortion, I used to have one that did that. It seemed to be exacerbated if I had the "loudness" switched in for some reason. But the amp sounds much better after it has been powered up for a while, so my suggestion would be just to leave it powered up all the time. It doesn't draw much power at idle, and that way it will always sound its best.
As for the turn-on distortion, I used to have one that did that. It seemed to be exacerbated if I had the "loudness" switched in for some reason. But the amp sounds much better after it has been powered up for a while, so my suggestion would be just to leave it powered up all the time. It doesn't draw much power at idle, and that way it will always sound its best.