LM3886 DC offset and hum

[gootee]

Hi Tom,

This is very interesting!!!
Could you pleas further explain this to us. This is the first time I hear about it.

RGDS

Pemo

Pemo,

Here are some links to similar explanations that I posted in the past, possibly with more details or better information:

http://www.diyaudio.com/forums/chip-amps/214085-one-more-lm3886-pcb-4.html#post3084015

http://www.diyaudio.com/forums/chip-amps/176410-odd-grounding-problem.html#post2351411

http://www.diyaudio.com/forums/tube...-noise-ground-due-power-tx-2.html#post2841838

Cheers,

Tom

 

[WSJ]

Does that transformer introduce noise as compared to a toroid or R-core?

As seen in my pic, the twisted power supply wires are right next to the transformer.
The wide band amplifier output noise is only 430 uV RMS.
What is your speaker output sound level at 430 uV RMS?

Here is a sales pitch for Toroidal Transformers.

Toroidal Transformer - Toroidal Transformer Home

The superior design of a Toroidal Transformer results in a power source product which offers many advantages over other transformers utilizing standard, laminated, power. Several powerful advantages offered by a toroidal transformer include the following:

Low, stray, magnetic fields.

Quiet, efficient, operation.

 

[bcmbob]

Thanks, I have only used Ts and Rs but I continue to see the laminated in a lot of posts. Why are they so prevalent in tube amps? Is that a completely different ballpark?

 

[WSJ]

Michael,

Make sure the inputs are shorted when making a noise test, the amplifier input wires act as an antenna when left open.

With an HP lab power supplty at +/- 25 V, I measured a LM3875 on a PCB with the input shorted, the output noise was 270 uV RMS.

 

[Pemo]

Pemo,

Here are some links to similar explanations that I posted in the past, possibly with more details or better information:

http://www.diyaudio.com/forums/chip-amps/214085-one-more-lm3886-pcb-4.html#post3084015

http://www.diyaudio.com/forums/chip-amps/176410-odd-grounding-problem.html#post2351411

http://www.diyaudio.com/forums/tube...-noise-ground-due-power-tx-2.html#post2841838

Cheers,

Tom

Thanks Tom, I´ll be reading.