Can I replace big trafo with small SMPS?

[FriedMule]

I have the possibility to get an old class A amplifier and I like it, but it'll suck power out of my sockets as if it had been in a dessert for months.

My idea is to remove the trafo only but keep everything else, and then "just" connect a SMPS's output leads to where the old trafo's leads did connect.

Is there anything wrong in doing that?
Should that not save a lot of external power usage?

[TimNJ]

I mean, Class A is inherently inefficient as is. Always <50%, probably in the area of 25-35% for most designs. If you are worried about efficiency, look at Class D.

[Kleinstein]

At higher power level a SMPS is not more efficient than a transformer. There is some advantage with regulating the voltage, but the difference is not very large.
At low power (like < 5 W) a SMPS can be more efficient, but at higher power the difference is not large anymore. It is there more a cost advantage.

The problem is the class A amplifier. The allways <50% and normally worse is hiding the real evil: the problem is that a class A amplifier has a high power consumption even when low output power is needed and for audio this is the normal case nearly all the time. The point to compare is more the idle power, not the best case efficiency.
For a comparable power level a class A amplifier may draw 100 W , a class AB more like 10 W  and a class D maybe 5 W.

[CaptDon]

The transformer itself is not inefficient and probably has filament windings, high voltage windings, mid voltage windings and possibly even a bias voltage winding. SMPS, not worth the effort by a long shot!!!

[strawberry]

SMPS may not help if circuit is sensitive to noise
class D one and only benefit is efficiency 85..95% and price. min THD 0.1% , bandwidth limited to 20kHz,

[james_s]

You are misunderstanding the reason a class A amplifier is inefficient, the culprit is not the power transformer but the inherent characteristics of the amplifier topology itself. If you want to save power, turn it off whenever you're not using it.