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Old 10th August 2011, 11:43 PM   #11
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Thank you Digits for the link, I've read the III parts, interesting and usefull
Maybe a part of the answer is adding some filtering caps, 100uF before the existing 100nF (before RC 1R/100nF). Same thing, 100nF before rectifiers.
Don't know if it will solve "plop" when powering off the amp.
It seems to be caps "discharging", not hum or hiss, the amp is dead silent.
I've to test DC offset too.
Swapping source for a CDP gave the same result as USB/DAC...

PS : same "plop" using standard ChipAmp dedicated PSU for LM1875.
This one is only a single bridge, without snubber.

Last edited by korben69; 10th August 2011 at 11:45 PM.
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Old 11th August 2011, 12:36 AM   #12
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Hi korben69

I have LM1875s which also "plop" less than a second after switch off. I think it is just something they do rather than something you have done wrong.

My LM3875s don't do it, but both LM1875 amps I have heard did this.

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Old 11th August 2011, 02:27 AM   #13
kroto is offline kroto  Indonesia
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mine too...
I think it is the LM1875 nature...
(not more than a second though)
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Old 11th August 2011, 06:40 AM   #14
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Try R1 as per datasheet against the plop. 100k-1meg are common values for it.
If you've always done it like that, then it's probably wrong. (Henry Ford)
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Old 11th August 2011, 12:47 PM   #15
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Many thanks to all of you for your support
I've noticed that R1 is optional in BrianGT design, BTW I let it unpopulated.
I'll give it a try this evening and let you know.
Nice tip pacificblue
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