Class A for home use
I see, the question is too common, nevertheless I'll try :-)
Please, suggest a _musically_checked_ schematics for power amplifier:
- with approximately 20-30W power peak (8 Ohm load),
- balanced (bridge) symmetric topology is preferable,
- MOSFETs in output stage are preferable,
- without capacitors and transformers in signal path,
- global NFB absence is preferable.
Try the Pass Labs Forum. Maybe an Aleph or a Zen amp.
As you can see, I have mentioned "balanced symmetrical" topology,
as one of the aim is to make an amplifier more power-effective.
Such topology is not "Nelson's path", I think :-)
could the front end of a Leach meet part of your requirement?
regards Andrew T.
Are you not looking for a class A amplifier? Efficiency and class A are not usually used in the same breath. The Aleph X is the closest I can think of.
Clearly you are not interested in single ended topologies because of the low efficiency.
Meaning you want a push-pull output stage.
Secondly, you have no preference for a balanced design or amplifiers in bridged mode, as long as it has a balanced entrance.
That means practically any low power Mosfet push-pull design will do with the following constraints :
- A symmetrical circuit.
- DC coupled.
- No global feedback.
The latter is arguemental, for the last 20 years audio designers are talking local feedback.
As that still leaves a number of possible amplifier designs you may need to make a couple of choices more :
- a fully discrete circuit ?
- without a DC servo ?
- Easy to build ?
- Maximum cost ?
If you do not object to opamps in a circuit and a opamp DC servo,
with a couple of IRF630/IRF9630, a 5534 opamp and a OP07 for the servo it is possible to build a reliable amplifier fast,
the circuit components are probably less than $10 per channel.
There are a number of circuits like that around with proven results.
!!!! Just an example, of course there are way better components, i just mentioned a couple of cheap components !!!!
Other designs may call for selecting the components, or the need for a scope to measure and tweak the circuit.
For simple designs downloading a small scopefile for the pc soundcard from your fellow russian at edu.ru and a simple tonegenerator will do.
Important questions may also be :
- What is in front of the power amplifier ?
- What kind of speakers does it need to power ?
much more efficiency rather SE or something like SuperSymmetric has.
I'll try to clarify:
- as I have said, I mean push-pull balanced topology with balanced input (I have
some ideas about discrete balanced line drive, but they are rather young :-),
- I'd prefer global NFB absence, but 5-6db feedback (to set output shifting and
output dumping factor) is not rejected at all,
- fully discrete,
- without DC servo; I'm not afraid of 100-150mV shifting :-) between balanced
- two PS are possible, for example stabilized +/-50V for all except for output stage
with single 30-40V PS,
- hard to build :-),
- cost... OK, I can say "not too expensive". At any case an amplifier sinks,
box and transformers will have the main cost, I think,
- I have a scope, a signal generator, a software to see FFT ans so on on PC,
- speakers have standard design.
Probably you can see, my English isn't perfect. Please, explain me these words
meaning: "front of the power amplifier".
I was thinking about similar circuit you are speaking about, but did not find time enough to realize - maybe later.
With "in front" i mean what pre you intend to use with the power amplifier.
I think you should take a look at Mr Erno Borbely site.
He did a modular balanced symmetrical Class A Mosfet power amplifier in the '90s.
One of the versions is DC-coupled.
In Class A it does 50 watts, if you'd like it less lower the bias or the voltage.
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