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
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.
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?
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.
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.
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