Noisy earth

revell · 12th March 2005, 01:13 PM

When I turn on my light while my music is playing, I hear a plopping noise coming from my speakers. At first I thought it was aproblem with ground in my house, so I disconnected the earth from the power distribution block. But this did NOT solve the problem, it just keeps plopping.

Any other gainclone owner who has this problem too?

breez · 12th March 2005, 01:29 PM

Yes, same 'problem'. Happens also with a commercial amplifier (Hitachi integrated, circa 80s).

revell · 12th March 2005, 01:35 PM

Quote:

Yes, same 'problem'.

But no solution?

It is getting weirder: I've run both monoblocks and the pre of an UPS which was not connected to any AC outlet (purely on batterie power), I turn on the light: PLOP
Is this still normal?

pinkmouse · 12th March 2005, 01:49 PM

Radiated RF noise. Check all your cables are screened properly. Other than that, try a 0.1uf cap across the input pins on the chip.

revell · 13th March 2005, 08:00 AM

Does the cap have to be on the chip or can I put it also on RCA connector (connecting the positive to the negative side)?

Franz G · 13th March 2005, 08:08 AM

The cap must sit directly at the positive and the negative input pin.

Nationals recommendation is 220pF for the LM3875.

Look here, page 4 and top of page 6:

http://cache.national.com/ds/LM/LM3875.pdf

Regards
Franz

Nuuk · 13th March 2005, 08:21 AM

Or what about doing something about the light switch that is causing the RF?

revell · 13th March 2005, 08:55 AM

Thank you for all the suggestions, I'll try putting the 220pf cap between pin 7 and 8.
This won't be easy, I guess because all the components are already soldered to the pcb.

Nuuk: I guess I could listen to the music in the dark

Nuuk · 13th March 2005, 09:00 AM

Quote:

Nuuk: I guess I could listen to the music in the dark

I'm a big fan of lateral thinking!

But if you get afraid of the dark, I think you can put a capactior across the switch contacts to get rid of the RF thatit generates. Perhaps somebody more knowledgable can comment on the exact cap required.

revell · 13th March 2005, 09:04 AM

This is probably a stupid question but I'm going to ask it anyway: is there an other way of saying 220pf. e.g. 2,2uf or 0,22mf
I can't find 220pf on the RS site

12th March 2005, 01:13 PM	#1
revell diyAudio Member Join Date: Jun 2004 Location: Kemzeke	Noisy earth When I turn on my light while my music is playing, I hear a plopping noise coming from my speakers. At first I thought it was aproblem with ground in my house, so I disconnected the earth from the power distribution block. But this did NOT solve the problem, it just keeps plopping. Any other gainclone owner who has this problem too?

12th March 2005, 01:49 PM	#4
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Radiated RF noise. Check all your cables are screened properly. Other than that, try a 0.1uf cap across the input pins on the chip. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

13th March 2005, 08:21 AM	#7
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Or what about doing something about the light switch that is causing the RF? __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

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12th March 2005, 01:29 PM	#2
breez diyAudio Member Join Date: Jul 2004 Location: Finland	Yes, same 'problem'. Happens also with a commercial amplifier (Hitachi integrated, circa 80s).

13th March 2005, 08:00 AM	#5
revell diyAudio Member Join Date: Jun 2004 Location: Kemzeke	Does the cap have to be on the chip or can I put it also on RCA connector (connecting the positive to the negative side)?

13th March 2005, 08:08 AM	#6
Franz G diyAudio Member Join Date: Jun 2004 Location: Bern / Switzerland	The cap must sit directly at the positive and the negative input pin. Nationals recommendation is 220pF for the LM3875. Look here, page 4 and top of page 6: http://cache.national.com/ds/LM/LM3875.pdf Regards Franz

13th March 2005, 08:55 AM	#8
revell diyAudio Member Join Date: Jun 2004 Location: Kemzeke	Thank you for all the suggestions, I'll try putting the 220pf cap between pin 7 and 8. This won't be easy, I guess because all the components are already soldered to the pcb. Nuuk: I guess I could listen to the music in the dark

13th March 2005, 09:04 AM	#10
revell diyAudio Member Join Date: Jun 2004 Location: Kemzeke	This is probably a stupid question but I'm going to ask it anyway: is there an other way of saying 220pf. e.g. 2,2uf or 0,22mf I can't find 220pf on the RS site

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