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Trevor Wilson[_3_] Trevor Wilson[_3_] is offline
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Default More than 30W per chanel Class A transistor amps

On 5/03/2019 5:11 am, wrote:
On Monday, March 4, 2019 at 11:32:18 AM UTC-5, Howard Stone wrote:
On Monday, 4 March 2019 16:06:40 UTC, Peter Wieck wrote:
On Monday, March 4, 2019 at 9:59:57 AM UTC-5, Howard Stone wrote:

Aha, this is an argument for active pre-amps. Passive pre-amps presumably all have no gain.

Correct. Passive pre-amps are no more than switches.

Peter Wieck
Melrose Park.


So I guess that, given that my project is about exploring Class A
with my speakers, that IF I buy a pre-amp, it too needs to be Class A.


The chances you're going to come across a preamp whose active
'stages are NOT biased class-A is pretty small. I can think of none
of the top of my head. (Some earlier IC-based preamp may have used
op-amps that had a push-pull output stage that may have run class
AB, but, again, I can think of none).


**I'm not certain about that. Obviously, depending on the load
impedance, many OP based preamps may, in fact, be operating largely as
Class A/B amplifiers. A system popularised back when the 5532/4 was
released, was to force it's operation into Class A mode, by inserting a
current source into the feedback loop. I've never measured it, but I
assume that suggests it is a largely Class B output stage, but by using
the kludge, becomes Class A (load dependent, of course). Maybe I'll
measure it one day....


And I suppose I find out whether there are any Class A DACs,
because I think their analogue end must involve some gain.


Same goes here as well: you're not likely to find a DAC output
stage that is NOT class-A biased.


**Not that it matters either, I agree.



NOTE: A "DAC" really consists of two fundamental parts: the
digital-to-analog stage, which, these days, will also
include the bulk of the anti-imaging filtering, done
in the digital domain: this part feeds an analog signal
to the line driver stage, which, again, is very unlikely
to be anything but class-A.



However, in a preamp, where the total power output requirements
are orders of magnitude less, these considerations become far
less of a design driver and thus do not force decisions between
biasing classes that are either engineering or economically
driven.

Putting it more simply, it's MUCH easier to design, manufacture
and support class A amplifiers dealing with low(er) signal levels
and substantially lower powers than it is to to the same where you
need LOTS of power.


**Quite so.


Don't spend a lot of time worrying about whither the preamp you
might buy is class A or class AB: because you'd be spending a HUGE
amount of time searching for the class-AB preamp that you don't want
to buy.


**Load depending, yes.


--
Trevor Wilson
www.rageaudio.com.au

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