"Le Mutant" Class A

[wrenchone]

Here's a picture of the new modules for the mutant bolted to a common heat spreader, with CPU coolers attached on the other side directly over the output devices. One channel biases up ok, the other has a problem which is likely to be a cold solder joint or a solder splash, as there's not a whole lot to go wrong with the circuit. I have to take the whole thing apart anyway to put some thermal grease on the CPU coolers, so its not a biggie to get the bad module sorted out at the same time. I'd say I'm close to getting some tunes out of this thing, even if it's just using a bench supply. I suspect that this amp will likely show up at Burning Amp with the same sort of impromptu setup I'm using for the "Half Nelson" (well, maybe a little prettier, but not by much).

[wrenchone]

I found the problem in the bad channel (open solder joint), and now both channels bias up the same. The CPU coolers definitely do their bit in reducing the temperature of the heat spreader.They're not really all that loud, even at full blast. The bias current is a little over my optimum (1.6A-1.7A vs. 1.5A). As soon as I get that tweaked to my satisfaction, it's tune time, even if I have to use a bench supply. This amp will get the 2 X 20V Antek toroid from my "Half-Nelson", which will in turn get one of the toroids I scored from Papa at the first Burning Amp in 2007.

[wrenchone]

Attached is the mutant that will be slouching its way over to this year's Burning Amp. I ended up with selected IRFP9240s instead of the IXYS P-channel guys I wanted to try, as I was able to select a pair of the IRFs that were a closer to the IRFP240s I had on hand than any of the IXYS fets. I ran both channels of the amp using my bench supply at work, and the sound was OK, but there were some issues with asymmetric supply rails, as the amps were really taking more current than the bench supply could handle without going into limiting on one side. I'll expect better results with a solid DC supply - in the works.

[wrenchone]

Le Mutant is going into a case raped/gutted from an old server SMPS - the case was smaller than I remembered, but the CPU coolers make the gain modules small enough so that everything will fit inside. This puppy may be up before the weekend's over. I wanted to fit the "Sic Puppy" inside this case, but the overall emphasis in big iron on that project won't let me. That one will probably end up looking like the "Half Nelson", but with a little more elegant implementation, thanks to more CPU coolers and some Corian.

[wrenchone]

Pictures of the Mutant will follow later today when I'm finished wiring the thing up and doing a power-up test. It's in an industrial case that used to belong to an old server supply - boring but functional, and PD small for a class A amp good for ~30W/channel.

[wrenchone]

Le Mutant is in the case, running, and making nice sounds, though it's hotter than I would like - that's Class A for you. Offset is about 15mV each channel. I'll haul it into work tomorrow to check it with the thermal imager and look at the square wave response.

[Nelson Pass]

I hope you will be bringing it to BAF. I have a nice system for you to plug into.

[wrenchone]

I'm rabbiting away (taking a break now for supper to cook), so there should be three Passish things for BA. None of them will be really pretty, but they all will work.

[wrenchone]

Le Mutant went to work with me. The thermal imager reports an output device case temp of ~80C, which means that the junction temp is probably over 100C. A lot of this is do to the insufficient maens for heat removal inside the chassis. The CPU coolers I chose to go on the heat spreader do a good job of pulling heat off the spreader, but then they sort of spray it around inside the chassis. I can put up with this situation long enough for a BA demo - what's Buring Amp without a hot amp, anyway? I may add another fan tie-wrapped to the front panel grille to pull some more hot air out - noiser but cooler. I have solutions coming that will allow me to better get the heat out of the chassis, but for the time being what I have is good enough to survive some demos.

I'm very happy with the square wave response - attached is a photo of the overall square wave response.

[wrenchone]

Here's a photo of the edge details - this amp is fast....