Excessively loud output

[glassglow]

I've been using a Mainline that I built for over two years without any issues whatsoever. I'd been using it lately with a pair of Focal Clears.

The upgrade bug bit me a few months ago so I replaced the stock Dayton output caps with a pair of Jantzen Z-Superior 10uF 800V caps. The Jantzens certainly sounded different and got better with use. I probably put something like 30 hours on them and then didn't listen to the amp for a week. When I turned it back on, the volume level through the Clears was now extremely loud, as in blow a driver loud. I checked the volume controls and they were where I usually had them. I immediately switched them to the most attenuated level and it was still extremely loud. I checked all the resistances and voltages again and everything was the same except that the bias had drifted from the 145V that I set it to when I installed the Jantzens to around 165 V. On a whim, I pulled the Jantzens out and put the Daytons back in. And what do you know, the volume levels were back to normal, which I did not expect.

Anyone have any ideas as to what caused this? It affected both channels identically.

[Paul Birkeland]

You almost certainly have a flaky solder joint that you bumped into when changing out the caps.  If you turned the level controls all the way down and the level was still super loud, then there's a ground wire or connection that's not well soldered.  When you find and resolder this connection, your amp may sound quite a bit better than it ever has.