Loud hum on Rotel Amp after about 30-60 minutes?

[AMackie]

Hi Everyone,

I registered on this forum in the hope someone can help me out...

I have just moved into a new home and my Rotel hifi system, which worked fine in my old home, has consistently started making a loud buzz after being on for about 30-60 minutes. I'm pretty sure it is due to static electricity as the sound of the hum changes when I touch the amp while it is making it. I asked a friend of mine who knows more of hifi's to have a look at it. He said he had the amp playing for a whole day (in his workplace) and it didn't make a buzz . He also opened it up and said everything inside looked fine... he didn't know what was wrong. I have tried plugging it into different sockets, I have replaced the speaker cables so that they are newer and shorter... nothing helps.

So somehow there is something about my current setup in my new home which is making the hifi buzz. I have no idea how to solve this...

Here's my setup: iPod into aux input of Rotel RC-9708X into Rotel RB-9708X.

Sorry for probably quite basic question... Any advice is appreciated!

Cheers

AMackie

 

[TrevC]

Hi Everyone,

I registered on this forum in the hope someone can help me out...

I have just moved into a new home and my Rotel hifi system, which worked fine in my old home, has consistently started making a loud buzz after being on for about 30-60 minutes. I'm pretty sure it is due to static electricity as the sound of the hum changes when I touch the amp while it is making it. I asked a friend of mine who knows more of hifi's to have a look at it. He said he had the amp playing for a whole day (in his workplace) and it didn't make a buzz . He also opened it up and said everything inside looked fine... he didn't know what was wrong. I have tried plugging it into different sockets, I have replaced the speaker cables so that they are newer and shorter... nothing helps.

So somehow there is something about my current setup in my new home which is making the hifi buzz. I have no idea how to solve this...

Here's my setup: iPod into aux input of Rotel RC-9708X into Rotel RB-9708X.

Sorry for probably quite basic question... Any advice is appreciated!

Cheers

AMackie

Disconnect everything from the input side, see if it still buzzes. Presumably the buzzing is from the speakers.

 

[gasolin]

Mabye it's time to upgrade i know the amp is about 20 years

 

[Thompsonuxb]

You may have an issue with your mains supply.

If the amp was fine at your mates but the buzz returns at home....

You may need mains conditioners. ......

 

[TrevC]

You may have an issue with your mains supply.

If the amp was fine at your mates but the buzz returns at home....

You may need mains conditioners. ......

Balls.

 

[Thompsonuxb]

You may have an issue with your mains supply.

If the amp was fine at your mates but the buzz returns at home....

You may need mains conditioners. ......

Balls.

Apologies to the OP, but it looks like I may have to go kick some #ss....

TrevC, it's been awhile.

Ok process of elimination - amp good at the previous premises, good at his mates buzz at home.

The amp is most likely, identifying an issue with his supply.

Maybe it's dirty mains, maybe the wiring in the property requires an assessment by a pro.

Etheir way a mains block - conditioner with surge protection is a temporary solution. Worth considering.

This I would suggest as the way forward. Or you can expand on your suggestion.

 

[mightyquin]

Mabye it's time to upgrade i know the amp is about 20 years

Why do you want the OP to spend more money when he's clearly identified that the amp isn't the problem? Presumably he'd have the same issue if he went out and spent £500 on a new amp. What would you suggest then?

 

[andyjm]

The OP isnt clear whether the buzz is coming from the speakers or the amp itself. Given that the amp works fine in another location, it seems that:

1. If the buzz is coming from the amp, it is probably the mains transformer saturating. DC offset on the mains has become more common with switch mode and non linear power supplies everywhere, so it is possible that mains DC offset is the cause. Why after 60 mins? - perhaps the transformer has to heat up before the laminations are free to vibrate.

2. If the buzz is from the speakers, then this would suggest a (signal) earthing problem. Possibly the input cables are faulty with poor earth connectivity, and moving the amp has exposed the problem. Were the same cables used over at the mates place when he tested it? Wouldn't explain the 60 minutes though.

3. Could be a combination of things. Poor shielding on input cables, new routing af cables close to mains lead due to new location, beginnings of failure on some aspect of the input circuitry that requires some time powered up to manfest itself. Individually insufficient to create the symptoms, but all together cause the problem.

Best advice would be to change one aspect at a time, and see if it makes a difference. I would guess substituting and re routing the input cables would be a good start (assuming noise is out of the speakers).

 

[Thompsonuxb]

The OP isnt clear whether the buzz is coming from the speakers or the amp itself.  Given that the amp works fine in another location, it seems that:

1. If the buzz is coming from the amp, it is probably the mains transformer saturating.  DC offset on the mains has become more common with switch mode and non linear power supplies everywhere, so it is possible that mains DC offset is the cause.  Why after 60 mins? - perhaps the transformer has to heat up before the laminations are free to vibrate.

2. If the buzz is from the speakers, then this would suggest a (signal) earthing problem.  Possibly the input cables are faulty with poor earth connectivity, and moving the amp has exposed the problem.  Were the same cables used over at the mates place when he tested it? Wouldn't explain the 60 minutes though.

3. Could be a combination of things.  Poor shielding on input cables, new routing af cables close to mains lead due to new location, beginnings of failure on some aspect of the input circuitry that requires some time powered up to manfest itself.  Individually insufficient to create the symptoms, but all together cause the problem.?

Best advice would be to change one aspect at a time, and see if it makes a difference. I would guess substituting and re routing the input cables would be a good start (assuming noise is out of the speakers).

 

Agreed....

But his wiring needs checking and his kit needs protecting. He'll probably find his bulbs have a short life too.

Get your mains evaluated by a qualified electriction asap.

 

[AMackie]

Hi Everyone,

Thanks for all the quick and helpful replies.

I indeed did not clarify whether the problem comes from the speakers or the amp... I thought it would most likely be the amp as the sound changes when I touch the amp while it is making the noise.

I also don't think it is an overheating problem. If I turn the amp off and on again when it happens it immediately stops the hum. I imagine that if something was overheating it wouldn't cool down so abruptly and I would still hear the noise when I turn it back on. On the other hand, when it makes the noise it starts soft and becomes loud within about 20 seconds, which I thought might be a sign of something getting progressively warmer.

The new flat is in an old 70s highrise building on the 15th floor... We've found some other things that have been a bit outdated so it would not surprise me if it were the same with the electricity suply. I will try and have the system evaluated by an electrician. In the mean time, what exactly would a mains conditioner do?

Thanks again for all the help.

Cheers

AMackie

 

[Thompsonuxb]

Your best bet is to pay a visit to your local Maplins and Google. Their explanation will be better.

Basically it should regulate the supply reaching your amp and protect it from any surges from the mains - that may damage your amp in time burning out it's PSU.