LM3886 noise when turn on the light switch

[linhoffan]

This is first post, I built a dual mono LM3886 with two 300VA transformer and 10000uf/63v cap per rail, the sould is pretty good overall, but everytime when someone mechanical turn on or turn off the light power and sometimes the Refrigerator Compressor also influence , my speaker will have "pia" noise, but this situation not happened for my previous power amp, except this the background is very silence, is anyone experience for this , thanks.

[infinia]

probably RFI interference ( spark gap transmitter)

Do more trouble shooting to discount other connections or gear / music sources.
show us your build for better advice
RF filters on audio input and/or on power entry
shielding enclosure
twisting wires to reduce pick up

[6L6]

Do you have 2.2uf DC-blocking cap on the input? If no, try it, that may solve your problem.

[AndrewT]

RF attenuation is required.
Unfortunately National do not show RF attenuation as compulsory in their datasheets and even show example schematic with no RF attenuation for the mains cables nor for the inputs.

[linhoffan]

Many thanks you guys suggestion, I will try the RF filter at input RCA socket, but any recommend for the value? how about 680 ohm +470pF

[ByronInLawrence]

The noise may also be coming from your ground. I'm assuming your amp has a safety ground going to the wall outlet. Your refrigerator may be injecting noise into your building's ground wiring, which is finding its way into your amp. Fortunately, there is a rather nice article on this web site which deals with this problem. Here is the link:
Audio Component Grounding and Interconnection
Chapter 2 deals, specifically with the problem of noise.

Good luck!

[linhoffan]

Actually I tried many power amp(none chip), only this Lm3886 have this problem, so I think may be the chip amp is more sensitive for power or environment, next action maybe I will add a regulated power supply(use LT1083), I have no idea is this work?

[AndrewT]

Don't regulate.

Attenuate the interference.

Fit an RF filter at the input of the chipamp.
Consider adding a filter direct across the RCA input sockets.

Fit mains filter. They are available ready built as IEC sockets with all the correct components inside. Obtain the lowest current rating that will safely power your equipment. They are usually available in 1A, or 3A, or 6A

A metal chassis completely enclosing your amplifier also attenuates interference, especially if you have unattenuated emissions coming from radios and motors around the house.

It is always better to attenuate interference at source. Move the mobile radio, the wireless alarm system, the wireless doorbell, the wireless computer network, etc.

Fit all motors especially and switches in general with a snubbing network. These too are available ready assembled.

[linhoffan]

Thanks all of your comments, I prepared the parts for RC filter will install tonight, I will update the result.

[linhoffan]

I add the RC filter, but doesn't work, attached the schematic, any ideas?

R1:22K
R2:22K
R3:1K
R4:22K
R5:1K
C1:100uf/35v
C2:100uf/35v
C3:100uf/35v
C4:22uf/35v
C5:1uf