Ditching Class A Amps due to Heat - Sort of a Poll

@atmasphere 

You've been taken in like all the other punters.

The Krell sliding bias system and its predecessors are cons.

The orchestra is noodling and so is the bias on the Krell.

Suddenly the guy at the back whacks the six foot drum for all he's worth.

The guy in the amp says 'OMIGOD the guy in the orchestra has whacked that drum.  For *****sake get that bias up immediately.'  The other guy in the amp on the bias hears the msg and turns up the wick.  But the guy in the orchestra on the big drum has already gone home.

YOU CANNOT UP THE BIAS QUICK ENOUGH TO CATCH THE MOMENT.

I have read the patent and it does not answer this.  It cannot.  I asked a senior engineer working on my KRS200s how it solves this issue and he could not answer.

This started as a con and remains a con.  The bias cannot be changed quickly enough.  The only way to do it would be to buffer the signal for a second or so which would introduce insoluable clock problems.

YOU CANNOT UP THE BIAS QUICK ENOUGH TO CATCH THE MOMENT.

I have read the patent and it does not answer this. It cannot. I asked a senior engineer working on my KRS200s how it solves this issue and he could not answer.

@clearthink You can easily change the bias no worries.

I don’t think they want to publish the trade secret which is why its not in the patent. You are correct that you do have to be careful that the timing of everything works out. That means that you have to have the same bandwidth in both the actual audio circuit and the circuit driving the bias so that they are in fact properly time aligned (IOW no phase shift between the two at any audio frequency). You can’t have any timing constants to filter noise! It simply has to be as reactive as the audio circuit itself.

I think Krell did that- its not hype at all. The problem is that this type of circuit by definition has to introduce distortion of its own. That, ultimately, is why we never implemented it in our amps.

In answer to the OP, I’ve got a pair of Pass XA60.8s, and living in MN, I appreciate that they are space heaters in the winter. Warm and cozy. In the summer, the extra heat is tedious and the a/c has to work harder to compensate.

I’d love to have the same sound without the heat; emphasis on same sound (or better). I’m watching the Atmasphere class D monoblocks carefully. I’d love to demo a pair, but our local dealer is a bit of a train-wreck. Still on the fence.

I’ve only had two class A amp, and one was just "strongly biased into class A"

One was a Musical Fidelity A100X integrated. That one I kept only two weeks: it was getting so damn hot after about 30 minutes of use that I was being paranoid all the time. Even the volume control was too hot to touch. You could have grilled a ribeye on top of it. Ridiculous. I had flatmates at the time, and the stupid girl once put her syllabi on top of it, while it was on. I saw that and started to have nightmares about the house burning down.

A couple years later I bought a Sony TA-N86B. That one was amazing and never got too hot to touch even when run in full class A mode. But it did put itself in protection mode every time the room temperature would get to a certain level in summer (and I don’t live in a tropical area!) until the amp’s PSU finally died of probably unrelated causes.

Then I discovered flea power, class D chip amps (that TA2024 from Tripath!) that sounded really lovely (with a little care) on my horns and I definitely gave up on everything else.

Now I have a multi-amped system and exclusively use tiny class D amps. The system sounds great, it stays on 24/7, doesn’t produce any heat, barely uses any electricity, and never sends nasty unwanted continuous current spikes in the fragile and unprotected drivers. They also only use as much floor print as two cigarette packs each.

In Belgium where I live, the energy crisis is an abomination. I have friends earning 2000euro per months, with a 900 euro rent, who now have to pay 500 euro in monthly energy bills. It’s a nightmare. I’m so happy I’ve got my class D amps!

I own a Pass Aleph 5 and, yes, it runs hot, but I don’t care. It sounds beautiful and that’s why I have it.