Trace Elliot power amp

[lowell]

Fixing this PA... 1 bad mosfet. Replacing both and both drivers. I'm curious if I'm understanding the design and theory of this circuit correctly. The zeners and diodes specifically. What I make of it is this: D7, D10, ZD5, ZD6 keep the mosfet gates no further than 12.7v from their sources. D8, D9, ZD3, ZD4 are keeping the driver collectors and TR3 base no more than 33.7v apart. If I'm correct is this some kind of transistor protection attempt? Maybe those mosfets are damaged when the gates and sources exceed that voltage?

On the road and phone ain't uploading schem. The schematic file is A100.50 for those of you who have access to TE schems. I'll upload it ASAP.

[Steve Conner]

Hey Lowell

The first set of diodes protect the MOSFET gates against overvoltage if the output gets shorted. The gate insulation in mosfets is very thin. It takes something like 50V to blow it out instantaneously, but the long-term odds of failure start to rise as soon as you get over about 12V.

The second set, as far as I know, are some sort of clamp to give cleaner clipping behaviour when the power amp is overdriven. They stop the driver stages from saturating, so they recover quickly from overdrive without hanging up. That means the user can overdrive it a fair bit without even noticing, giving the illusion of more headroom.

[J M Fahey]

Hi Steve. I'm reading "The Hanging Shed" by Gordon Ferris, set in the Glasgow back alleys (East End and Gorbal's Cross) in the late 40's.
Creepy place !!! Gives me the shivers.
Very well written , though.
PS: I love cooking, and it gave me ideas. Will try my hand at making "a pie".

[Steve Conner]

The East End of Glasgow is pretty badass even today.

I haven't eaten a pie in a while. I used to love them with baked beans on top.