Rotel RB980BX power amp hum and "pop"

metako · 4th June 2008, 06:53 AM

I just plugged in for the first time a Rotel RB980BX power amp that I bought off ebay and there is a hum in both speakers (this is with preamp connected to power amp but the preamp not turned on). Its louder in the left speaker and when I pull out the interconnects from the preamp (which has its power off) the hum gets louder. The Rotel only has a 2 pin AC plug. Does this sound like failed power supply caps? Is there an easy way to test the caps without complex equipment? (I only have a mulimeter). Why do the interconnects affect the level of the hum?

Also, there is a loud "pop" when I switch the power amp off! The amp has a delayed power on so I didnt think it would pop on switch off. Would cleaning fix this or has a part failed?

Seller said the amp was in excellent working order so has misrepresented it. Like to know what I'm up for before I contact him. I swear this is the last time I buy something off ebay without hearing it! Thanks.

Mooly · 4th June 2008, 07:03 AM

Hi, It's going to be more involved than that, for sure. You need a meter to do measurements and possibly a circuit-- depends on how experienced you are.

metako · 4th June 2008, 07:15 AM

Havent been able to find a circuit for it except the clone given in the thread below and I dont know how close to the Rotel it is.

Raise psu voltage

Also I dont know alot about amps so I guess I'm in trouble!

Mooly · 4th June 2008, 07:19 AM

Have you a meter

metako · 4th June 2008, 07:20 AM

A multimeter yes.

Tube_Dude · 4th June 2008, 07:22 AM

Hi

Have you inspect the obvious?... the fuses!

metako · 4th June 2008, 07:25 AM

Can the fuses cause hum???

Mooly · 4th June 2008, 07:25 AM

Check with meter on DC volts and with no speakers connected whether there is any voltage present at the speaker terminals.

Tube_Dude · 4th June 2008, 07:27 AM

Quote:

Originally posted by metako
Can the fuses cause hum???

IF the amp is working with only a voltage rail, yes!

metako · 4th June 2008, 07:39 AM

measuring across pos and neg of each speaker terminal there is 0.026V on right and 0.048V on left.

Tube_dude can I measure the fuses or just replace?

4th June 2008, 06:53 AM	#1
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	Rotel RB980BX power amp hum and "pop" I just plugged in for the first time a Rotel RB980BX power amp that I bought off ebay and there is a hum in both speakers (this is with preamp connected to power amp but the preamp not turned on). Its louder in the left speaker and when I pull out the interconnects from the preamp (which has its power off) the hum gets louder. The Rotel only has a 2 pin AC plug. Does this sound like failed power supply caps? Is there an easy way to test the caps without complex equipment? (I only have a mulimeter). Why do the interconnects affect the level of the hum? Also, there is a loud "pop" when I switch the power amp off! The amp has a delayed power on so I didnt think it would pop on switch off. Would cleaning fix this or has a part failed? Seller said the amp was in excellent working order so has misrepresented it. Like to know what I'm up for before I contact him. I swear this is the last time I buy something off ebay without hearing it! Thanks.

4th June 2008, 07:22 AM	#6
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	Hi Have you inspect the obvious?... the fuses! __________________ Jorge

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4th June 2008, 07:03 AM	#2
Mooly diyAudio Member Join Date: Sep 2007	Hi, It's going to be more involved than that, for sure. You need a meter to do measurements and possibly a circuit-- depends on how experienced you are.

4th June 2008, 07:15 AM	#3
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	Havent been able to find a circuit for it except the clone given in the thread below and I dont know how close to the Rotel it is. Raise psu voltage Also I dont know alot about amps so I guess I'm in trouble!

4th June 2008, 07:19 AM	#4
Mooly diyAudio Member Join Date: Sep 2007	Have you a meter

4th June 2008, 07:20 AM	#5
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	A multimeter yes.

4th June 2008, 07:25 AM	#7
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	Can the fuses cause hum???

4th June 2008, 07:39 AM	#10
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	measuring across pos and neg of each speaker terminal there is 0.026V on right and 0.048V on left. Tube_dude can I measure the fuses or just replace?

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