Ashdown thermal problem

[Axtman]

When my Ashdown ABM400H is cranked the the bass is played hard the output suddenly cuts out. If you unplug and replug in the speaker cabinet the amp works....until you push it again. Is this normal thermal overload protection or do you supposed there is something wrong with the amp?

BTW I find that the shutdown problem is exacerbated by engaging the subharmonic effect.

[Enzo]

Isolate the problem.

Are you unplugging the cab from the back of the amp? assuming so, unplug the speaker cord at the cab end instead. Does that also wake it back up? Possibility being that the act of pulling a plug out and pushiing it back into the amp might be the deal rather than some thermal.

If a thermal is kicking in, the amp would be hot to the touch, real hot. And thermals are reset by cooling down, not by simply popping the plug out for a second.


Have you tried connecting this head to a different cab, and using a different speaker cord?

Are you using an actual speaker cord, and NOT just a guitar cord to connect the head and cab?

Ball up your fist and whack the amp on top when this happens. Does that jolt wake it up? And for that matter, when it is working right, does hitting it cause any reaction? The amp should not react at all to a whack.

And if there are any FX loops, plug a spare cord from send to return, any help?

[Axtman]

I think I figured out what the problem was. BTW, the other day I could not get the amp to shut down no matter how loud I played. Yesterday I opened up the amp and looked around. I went to test how hot the heatsink was getting and noticed that if I pressed on the heatsink the relay would kick and shut the amp down. So I disconnect the output board and looked around. I could not find a broken trace but did find that 2 of the output transistor leads seem to have cold solder joints. So I resoldered the connections. Now I when I press on the heat sink the amp does not cut out.

I also found that the 3 wires from the preamp board to the power amp board were acting microphone. I rerouted the wires and twisted them around tighter.

I hope that this solves the problems.