Noise in the loudspeakers when my LM1875 are turned on

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LM1875 has no mute circuit and requires one for both turn-on and especially turn-off. Else you will hear that pop.

I use the one below
 

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I've used this one in another application. It seems well made and will do the job although it needs a (small) separate supply I you want to avoid turn-off thump /noises too. It also provides DC offset protection.

UPC1237 Speaker Protection Board AC 12V-24V OMRON Relay for stereo 2 channels Amplifier
AliExpress

I modified mine so that it would (hopefully!) "crowbar" the amp should the relay contacts weld due to high current, protecting the speakers - however that scenario seems unlikely with an lm1875.

The supply transformer I used was this one

PE2820-I Power 3VA 230V/12V Expory resign encapsulated safety isolating transformer PCB Welding transformer power transformer
AliExpress
 
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