Any kit/board suggestions?

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you can drive that stuff way harder than you should with voltage...
my cuzen runs mosfets at over twice there voltage rating...
if you want it to last long i would NOT recommend it unless you know what you doing
it doesn't usually hurt anything if its kept cool but not for faint of heart
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The amplifier module example linked is certainly cheap for the amount of power but is too compact, considering the amount of heat necessary to be dissipated. The heatsinks will be unnecessarily complex and likely expensive to adapt and thus cool properly. The electronics are actually the cheap part of high power amplifiers.

If your aims are only for a more modest 350W, spend your money on a better design that is suited to the transformer rating and will be more robust in the long run.

Perhaps you might consider something easier to mount to a heatsink as well, like this MOSFET model. LME49830 K1530 J201 300W Mono Power Amplfier Board | eBay
Thanks for the input. I have been looking at oem designs as well, to get a better idea of general layout/design of output devices.
That lm49810 board is only about half of what I have available in the PS, is rated at 4 ohms...
The Parasound hca1200 has around 10 transistor pairs per channel, is rated around 300 per side.
Am thinking that by not running at the edge of the limit, sq will benefit?

I have a large pile of heatsink extrusion here as well, but I do agree that trying to run that board I referenced at its advertised power would be, well, difficult. Figuring that the transistors would put out around 150 watts of heat, max, per pair, I can't imagine trying to keep it cool at the advertised levels!

That said, do you see anything wrong with running those boards at less than 30 percent of their max, or anything wrong with the layout?
I would be using a decent preamp with them.
Another path may be to leave the 90 plus volt rails for another project/future upgrade and use two of these 24v 600w ps instead;

A pair in series would get the voltage down to more reasonable levels, still would make plenty of power. I have a few of these around as well. The amp rating should be more than enough.

Should be fun, have plenty of machining experience to make some heat sinks using the extrusion I have along with some .375 plate.
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So you meant 70V AC windings rather than DC power supply output? That raises the power capability from 300W/8R quite a bit and does mean a heavier amplifier than I suggested. That's a pity because the module is a good design using respectable components and has great specs. though I'm only speaking from the published details which appear genuine as usual, in my experience with that trader.

Many people now look at SMPS as a cheap solution to power costs. You do have to know how to keep the RF out the amplifier though and in a high power amplifier, that could be a real problem.

IIRC, Parasounds use TO247 BJT outputs which are not quite the same as VMosfets in that less power can be safely extracted from them and VMosfets generally work better with hot bias of some hundreds of mA. 10 pairs of TO247 could be said to equate to 5 pairs of the same chip in TO264 pack as far as thermal dissipation and case temp. is concerned but not all designers have the same priorities so I don't think there is necessarily any benefit in lots of redundant output devices unless you are going to occasionally blow everyone away with massive sound levels or just like the idea of 10x power overkill for a security feeling.

Nonetheless, if you have 100V rails, you have to think in terms of 600W amplifiers and for that I would look at Aussie Amplifiers in the commercial sector of this forum - not because of any local affiliation, but he does supply good, high quality product and support at fair prices and I think now, much as Bob Cordell in the high power stakes. i.e. You would be crazy not to go Mosfet if only for the reliability factor, cost and easier parts and set-up tolerances.
"looks like someone will need a big heatsink"

It's designed to b be fan cooled.

"I would look for a complete module with power amp and heatsink.
Drilling heatsinks can be a mine field.
Firstly you really need to put the transistors on a heatsink before they are soldered or the legs get strained when screwed down.
Then there is the problem of swarf and burrs on holes cutting through insulators. "

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