[Eeyore]

Trevor Wilson wrote:

"Eeyore" wrote in message

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

**We all have. Pretty much every amplifier operates Class A to a few tens of
milliwatts.

That's not what I meant by true Class A though.


Plenty loud enough for quiet listening. Some high bias Class A/B
designs operate to a couple of Watts in Class A. Even with 90dB/W/M
speakers, this is pretty loud.

Sure enough but what you need to be aware of is that working in the crossover
region the output device transconductance is varying widely and putting
non-linearity into the transfer characteristic


For my own part, I am very familiar with an
amplifier which has user switchable Class A operating points. Since the
design eschews the use of Global NFB, it is far more sensitive to bais
current changes than most high Global NFB designs. Once the Class A
operating point goes beyond 10 Watts Class A, there is bugger all
difference.

In this case the crossover point has 'moved up the scale' and has less overall
effect as a percentage of signal level. It doesn't totally go away though.


Except, when using the thing on a US power receptacle. At 100
Watts Class A, the power consumed from the mains supply is too high for
regular US outlets, without losing mains Voltage.

Really ?


At 100 Watts Class A, in
the US, the sound becomes slightly 'compressed'.

I find some difficulty believing that.


Pretty much anywhere else
on the planet is fine.


Any comments on how it sounded compared to any other types ?

**IMO, Class A is used by so-so designers who can't figure out how to design
an amplifier properly. Once bias current is set above the 'knee' of the
device (around 100mA for BJTs and 1 Amp for MOSFETs) any more Class A bias
is superfluous.

There are still some advantages in not turning the devices hard off though.


Think of it this way: A badly designed Class A/B amplifier will probably
sound better when operating in Class A. A well designed Class A/B amplifier
will probably sound slightly worse when operating in Class A.

I can't understand the rationale for your 2nd idea there.

Graham