Using EI-Transformers instead of SMPS in Class D Chip amp PSUs.

[Ronj]

Hi,

Is there any specific technical reason why most of Class-T and TDA designs use SMPS power supplies? I know the obvious ones such as probably low cost, size and efficiency.... Other than these?

Or Is there any technical problem in using EI transformers to make power supplies for say an amp based on Tripath TA2024 chip or NXP TDA8930BTH chip?

Thanks,
Ron

P.S:- This question probably have been asked here before, had I located the T-Amp FAQ, I probably could have avoided posting this thread. But the FAQ is nowhere to be seen.

[81bas]

Many Class-D designs have bad PSRR (power supply rejection ratio), even many selfoscillating designs... So it is almost always preferred to use some kind of regulated power supply for class-D amp, I would say...

[theAnonymous1]

Here is a monster I built using EI core transformers.....

IRAUDENSTEIN: A parts bin monster

It was built for potential subwoofer duty, but it sounds surprisingly good used as a full range amp. The outputs are almost dead quiet without an input signal.

EI pros:
High input DC immunity
Lower bandwidth = less line noise on the outputs
Low inrush current

EI cons:
Larger size/weight
Higher stray magnetic fields
They like to hum

[81bas]

IRAUDAMP is exactly an example with very good PSRR value, since it uses an integrator in the feedback path, which provides very high loop-gain...

[theAnonymous1]

Originally Posted by 81bas

IRAUDAMP is exactly an example with very good PSRR value, since it uses an integrator in the feedback path, which provides very high loop-gain...

Lucky me then.

[Ronj]

Originally Posted by 81bas

Many Class-D designs have bad PSRR (power supply rejection ratio), even many selfoscillating designs... So it is almost always preferred to use some kind of regulated power supply for class-D amp, I would say...

I have seen KingRex's TA2020 design use a Toroidal transformer for the power. Not sure whether it's just a normal bridge rectifier or a regulated design.

@81bas:- So what do you think about using a EI transformer without a regulated power supply for a TA2024 amp running on Single rail supply? The amp can operate between 10-16v easily I guess...

Thanks,
Ron

[Pafi]

EI pros:
High input DC immunity
Lower bandwidth = less line noise on the outputs
Low inrush current

DC immunity? How do you mean? On power input? It's not immune, it's very sensitive! On audio input? Why would it be different?

Lower bandwidth? Maybe, but it has only 6 dB/octave slope, while an SMPS has 2 filter stages (12 dB/octave) at least!

Low inrush current? Yes, with soft-start circuit. But SMPS can also has soft-start circuit.

[theAnonymous1]

Pafi,

They were comparisons to traditional toroidal mains transformers, not SMPS.

[wwenze]

Have a TA2024 amp powered from a donut, linearly regulated to 12V. TA2024 has pretty tight voltage requirements (min 8.5V, typ 12V, max operating 13.2V), 16V is the absolute max before damage, not operating condition.

[DJNUBZ]

Let me see if I understand this.

Class d amps generally use SMPS PS because they have low PSRR.

Don't SMPS have a reputation for being noisy? Wouldn't that be a bigger problem with a class D?

I thought that people used SMPS with class D for the weight savings + some archaic notion that you need to use "like" with "like". Sort of like the old school tube guys.