my amp makes a loud hum

wonder_b · 26th May 2004, 11:25 AM

I have a eti480 amp it works fine on the computer but when I plug it into the head phone or rca plug in the tv ( new panasonic flat screen) it makes a very loud hum. can anyone tell me whats up

hjelm · 26th May 2004, 12:20 PM

Guessing here but your mains is earthed?
Then i think you have a ground loop between the tv and amplifier, via the earth in the wall.

DRC · 26th May 2004, 04:07 PM

A lot of TV's dont have an earth (double insulated) so my guess that what you can hear is the frame sync pulses leaking throught to the audio. This is typically at mains frequency (50 or 60Hz) but is NOT phase locked. I have come across this (in fact it happens without fail

) with CRT televisions and assumed it to be due to scan coils but you may be getting it with a LCD too

Can you hear this with a decent pair of 'phones plugged in instead ??

Also, do you have any kind of cable tv / broadband connected to the tv ??

wonder_b · 26th May 2004, 09:40 PM

no I cant hear hum with head phones or with pc speakers only the amp . I have tried eathing the amp case and the center tap but made no diff. hum is about 50hz same as power and runs at full wattage I need earmuffs to stay in the room

hjelm · 27th May 2004, 06:08 AM

If the TV doesn't have earth unconnect all other cales but the power to see if it helps. My guess is the antenna cable is connected to the same ground as the RCA or headphone.
Doesn't help you much but if it is the antenna then it is possible to build a hp filter to block the 50Hz.

wonder_b · 27th May 2004, 10:50 AM

I found the problem it had something to do with the rca block on the back of the amp and the input wires on one of the amps was on wroung way round its all good now it only has a small hum when it pluged into the tv now about 1w can only hear it when tv is on mute

26th May 2004, 11:25 AM	#1
wonder_b diyAudio Member Join Date: May 2004	my amp makes a loud hum I have a eti480 amp it works fine on the computer but when I plug it into the head phone or rca plug in the tv ( new panasonic flat screen) it makes a very loud hum. can anyone tell me whats up

26th May 2004, 12:20 PM	#2
hjelm diyAudio Member Join Date: Nov 2003 Location: Västerås	Guessing here but your mains is earthed? Then i think you have a ground loop between the tv and amplifier, via the earth in the wall. __________________ Hjelm

27th May 2004, 06:08 AM	#5
hjelm diyAudio Member Join Date: Nov 2003 Location: Västerås	If the TV doesn't have earth unconnect all other cales but the power to see if it helps. My guess is the antenna cable is connected to the same ground as the RCA or headphone. Doesn't help you much but if it is the antenna then it is possible to build a hp filter to block the 50Hz. __________________ Hjelm

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26th May 2004, 04:07 PM	#3
DRC diyAudio Member Join Date: Jan 2003 Location: UK (south west)	A lot of TV's dont have an earth (double insulated) so my guess that what you can hear is the frame sync pulses leaking throught to the audio. This is typically at mains frequency (50 or 60Hz) but is NOT phase locked. I have come across this (in fact it happens without fail ) with CRT televisions and assumed it to be due to scan coils but you may be getting it with a LCD too Can you hear this with a decent pair of 'phones plugged in instead ?? Also, do you have any kind of cable tv / broadband connected to the tv ??

26th May 2004, 09:40 PM	#4
wonder_b diyAudio Member Join Date: May 2004	no I cant hear hum with head phones or with pc speakers only the amp . I have tried eathing the amp case and the center tap but made no diff. hum is about 50hz same as power and runs at full wattage I need earmuffs to stay in the room

27th May 2004, 10:50 AM	#6
wonder_b diyAudio Member Join Date: May 2004	I found the problem it had something to do with the rca block on the back of the amp and the input wires on one of the amps was on wroung way round its all good now it only has a small hum when it pluged into the tv now about 1w can only hear it when tv is on mute

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