To the original poster, I too have noticed the exact same problem. After 20 minutes of play, the sound distorts and fizzles out. I am using the bugle power supply. This just started happening last week out of the blue. I've been using this setup for about four years now. If I unplug the power supply and plug it back in, it's good for 20 minutes. It also helps if I unplug the right channel + and - from the back of the cart, and put them back on...
I'm going to go over the Bugle and see if there are any cold joints, maybe replace what parts I do have on hand. I just need to get my soldering gun back. I'll report back at the end of next week.
Thank you,
Robert Mills.