[Bertie the Bunyip]

Eeyore wrote in
:



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



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bertie