Are class II switch mode laptop power supplies OK for audio amps?

[mjbmikeb2]

Looking to avoid ground loop problems by using a pair of class II/double insulated power supplies to give +20-0-20v rails for powering a class AB TDA7293 https://www.st.com/resource/en/datasheet/tda7293.pdf

The amp module is this one TDA7293 Digital Audio Amplifier Single Channel AMP Board AC 12V 32V 100W-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

 

[JonSnell Electronic]

They are fine assuming voltage and current rating is correct.

 

[29285]

Looking to avoid ground loop problems by using a pair of class II/double insulated power supplies to give +20-0-20v rails for powering a class AB TDA7293 https://www.st.com/resource/en/datasheet/tda7293.pdf

The amp module is this one TDA7293 Digital Audio Amplifier Single Channel AMP Board AC 12V 32V 100W-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

Ground loops are one problem, ClassII switching supplies generating substantial common mode noise another.

I recommend single PE-grounding of the secondary circuitry.
btw - there is really nothing "digital" on that TDA7293 pcb - just marketing blurb.

 

[mjbmikeb2]

Ground loops are one problem, ClassII switching supplies generating substantial common mode noise another.

I recommend single PE-grounding of the secondary circuitry.

Ok I had a look through my junk pile and found 2 double insulated plugpacks that have mains frequency transformers with AC outputs. however they have different voltages. One is 12V AC and the other is 16V AC. I could rectify and smooth these.

Aside from the asymmetric clipping behaviour would the differing rail voltages produce any other side effects?

 

[29285]

Ok I had a look through my junk pile and found 2 double insulated plugpacks that have mains frequency transformers with AC outputs. however they have different voltages. One is 12V AC and the other is 16V AC. I could rectify and smooth these.

Aside from the asymmetric clipping behaviour would the differing rail voltages produce any other side effects?

I did NOT exclude switchmode powersupplies - I use them with my guitar amps as well. But the secondary side should be grounded anyway.

 

[JonSnell Electronic]

Obviously you must ground the amplifier chassis, whether using computer power supplies or the correct power supply, to make it safe for use.

 

[mjbmikeb2]

Obviously you must ground the amplifier chassis, whether using computer power supplies or the correct power supply, to make it safe for use.

I though the whole point of 'class II/double insulated' was to remove the need for a mains protective earth connection. Class II plugpack power supplies usually have no earth pin. If an earth pin is present, it isn't connected to the secondary.

 

[mjbmikeb2]

I did NOT exclude switchmode powersupplies - I use them with my guitar amps as well. But the secondary side should be grounded anyway.

Why does the secondary need to be grounded when using a class II/double insulated power supply?

 

[abraxalito]

The grounding isn't really for safety its for providing a path for the aforementioned common-mode noise to return to source.

 

[mjbmikeb2]

The grounding isn't really for safety its for providing a path for the aforementioned common-mode noise to return to source.

Isn't that normally provided by a class Y capacitor inside the power supply as explained here
switch mode power supply - What does the Y capacitor in a SMPS do? - Electrical Engineering Stack Exchange

 

[29285]

Not at all. The Y-cap shorts rf-noise to comply with EMC-requirements. At the same time it is the source of all evil, increasing audibile common mode noise.