Spectron vs Parasound vs Cary vs ?

I'm a bit confused but perhaps what Audiozen is trying to say re voltage "fluctuations" is that in an unregulated power supply the voltage must drop significantly in order for the transformer to produce current. Load the amplifier further and the voltage will drop further and the transformer will deliver more current than its rated value, potentially overheating it?

Al has it right though. Power dissipation, however that happens, is the producer of heat. The Magtech runs cool because its transistors have an extremely linear transconductance function and therefore do not require much bias to eliminate crossover distortion. Most of the heat produced in a Class AB amp is produced by the bias current. The sole purpose of the bias current is to eliminate distortion. Through the use of linear “Thermal Trak” transistors very little bias current is needed to eliminate distortion and the amplifier as a result runs cool.

Nice beat down Al.

+1

"I also don't question the possibility that the approach to voltage regulation, used in that design, (the Magtech), may be a significant contributor to its high efficiency and cool temperatures..Al" This statement Al acknowledges the very point I'm making. I had a two hour conversation with Roger Sander's three weeks ago on this very issue. Different designer's, as he explained, take different approaches to regulate voltage attempting to stabilize the voltage to improve the efficiency of the amp.
Some methods work better than others, and in some cases, according to Coda engineers I spoke to, voltage regulation can cause an amp to blow up if not done properly. Again, high heat dissipation in an amp causes the amp to get hot due to unstable, fluctuating voltage. The focus here is LINEAR VOLTAGE REGULATION. To say that power consumption creates heat is not accurate since its unstable flucuating voltage that causes the heat problem. If you take any high powered amp on the market that runs extremely hot, and install the Sanders linear regulator, the amp will run much cooler according to Roger which is why his design is patented so others cannot use it and keep it exclusive to the Magtech amp.

Efficiency of most class D amplifiers are among the specs if not at amplifier manufacturing web site hen at original vendor e.g. B&O web site.

For example, our amplifier, Musician III has efficiency of 92%.

Efficiency has nothing to do with the stability of the power supply (and sound quality, in principle) as Almarg pointed out. Where its important are two areas: a) your utility bill and b) the size and weight of your amplifier.

For example, we have 1300VA Transformer in PSU and efficiency is 92% then "effective transformer" is in essence 1300 x 0.92 = 1195VA

If we compare it with typical class A amplifier where efficiency is about 25% then it needs:
1195 VA / 0.25 = 4800 VA (real life) Transformer. What it does with such transformer its different matter but it adds weight to the amp; and multiple additional heatsinks add cost and weight as well.

Yet, many class A amplifiers are simply magnificent and many are simply ear-piercing machines.

Simon

The discussion has to do with excessive heat problems. The more efficient the amp is the cooler it will run which is why Class D amps run cool due to pulse width modulation
which moves well over 90% of the current at a constant stream to the output. Class D amps have transfomers, transistors and power caps just as A/B and A amps but they run cooler since there is far less build up of wasted current not going to the output. Again, as I indicated in my conversations with Roger Sanders, His patented linear voltage regulator keeps the voltage stable and eliminates voltage flucuation which increases the efficiency of the amp so there is minimal wasted current which results in caps and transformers putting out very little heat resulting in his amp running just about as cool as class D amps because of higher efficiency.