This would benefit from some resistance being placed in the source circuits of the output devices to reduce the chance of thermal runaway. As a head amp I'm sure something like this is OK, though I've never tried anything like this myself.
A note for anyone with boards yet to build: The boards were not designed for verticals - for a power amp DO NOT simply drop in verticals! There will be smoke and tears! Seriously, they could be properly adapted by those who know what needs to be done.
A note for anyone with boards yet to build: The boards were not designed for verticals - for a power amp DO NOT simply drop in verticals! There will be smoke and tears! Seriously, they could be properly adapted by those who know what needs to be done.
Haha - that's a good warning. I plan to make the BC550 bias Vbe spreader a BD139 flying leads attached to hexFET for temp compensation. Alternatively, using a smaller power supply and lower rail voltages and current limit resistor can also prevent it from running away.
I meant IRF610/9610 in above post. If you want to use a board that can accept vertical hexFETs use the CFH7 - it's all set up with proper Vbe multiplier for temperature compensation. Has same topology, but with simpler resistor based current sources.
http://www.diyaudio.com/forums/solid-state/294834-cfh7-amp.html
http://www.diyaudio.com/forums/solid-state/294834-cfh7-amp.html
If I'm deciphering the photo correctly they form a "lifted" input ground to help prevent ground loops. R3 provides a slightly resistive ground path while the two diodes prevent the input ground from straying more than 0.6V from ground potential for safety purposes.
Yep, Jeff has it. Lifted input ground. It can be considered optional if found to be unnecessary.
Strange thing ; I'm using one Cap Multiplier psu for both channels .One channel connected no hum , as soon both channels connected result hum .
I tried a lot of things with no luck .
The FO 1.2 had the seem issue .I suspect the D1-2/R3 combo could be wrong of course .
The FO 1.2 had the seem issue .I suspect the D1-2/R3 combo could be wrong of course .
You have ground loops happening. The lifted input ground is actually there to help with this problem. The best cure for your problem is independent supplies for each channel. This also helps create a better stereo image in most amplifiers. If they are going to share a common transformer you need the input lifted ground to keep supply returns going back through the correct supply.
I have had builds where the loop breaker oddly made hum / buzz worse rather than better. Try either a jumper over the components, or remove them and run a separate wire from the input ground back.
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