Aleph 5 Query

[batteryman]

Thermal grease should lower the temps on all of them. It might even fix the "hot" one if the surface under it is rougher or has a slight dimple or something, but it's not a smoking gun like a burr would have been.

I doubt very much there's a burr on the ceramic (which has a honed finish) or the MOSFET (which has a ground finish).

Are you 100% sure there's no ridge around the "hot" hole? (Did you run a stone or diamond hone or something across it?)

On the MOSFET matching, how did you connect G to D? (Some of us were using patch wires and experiencing oscillation which threw the numbers off. They need to be connected right at the device.)

I shorted g-d with a croc clip - they were not on a heatsink at the time so testing was quick.
Thanks - I will re check the heatsink when I use the hs grease.

 

[batteryman]

FRYING TONIGHT - A5 FAIL

Well it was working fine yesterday and did sound better than my Quad 405.

This morning, after about 30mins, it almost burned the house down. Slight exaggeration but there was a lot of smoke though none of the mosfets look visibly affected.

It was still working despite the smoke, and the speaker protection had not tripped but not sure for how long.

After 55years wielding a soldering iron, I am clearly past building such a demanding project!

 

[JeffYoung]

It might not be so bad: a cold solder joint could generate enough heat to scorch a resistor, or a resistor overheating might burn off the paint. It's worth taking a look at all the components and see if you can see what got too hot....

 

[batteryman]

It might not be so bad: a cold solder joint could generate enough heat to scorch a resistor, or a resistor overheating might burn off the paint. It's worth taking a look at all the components and see if you can see what got too hot....

Yes, hopefully you'll be right. Nothing looks burned and the solder has not melted (it is leaded) so it is a mystery and is probably that rogue mosfet.

I will revisit it in a few weeks if the 40watt hybrid (opamp + dual complimentary BJTs with zero feedback) Class A amp from the usual place is not any good. (doubtful its truly pure Class A and there will be neg feedback somewhere but it's ready built and no schematic is available)