High pitch noise issue - HELP!!

Greetings all,

Having a problem with my setup - when pre and power amps are on, i hear a very soft but high pitched sound from both channels.

Would very much appreciate some advice on this issue.

My (initial) setup:
Rotel 1080 power amp, Rotel RSP960AX Pre Amp.Mirage F2 speakers, Tara Lab interconnects, QED Qudos cable. Rotel equipment was purchased 2nd hand, from a reputable dealer.
With this setup I would hear a high pitched sound from both channels if i placed my ear right up to the speaker. The sound was practically inaudible, and so it didn't worry about it.

I recently upgraded the pre-amp to a Rotel RTC-965, also purchased second hand (but not from a dealer). Pre amp was in as-new condition, never used apparently. Now, with just the pre-amp and power amp on, i can hear the sound within a few metres of the speakers, providing the room is quiet. It appears to be higher in pitch.

At first i assumed it was a grounding/power related issue, so i 'invested' in one of those circuited, isolated power boards. However this has made no difference.

To confuse(?) the issue, i have found one instance where the sound is almost eliminated. If i select a source with is connected via optical cable (SPDIF connection to my MD deck) then the sound is barely audible. Otherwise, it is always there regardless of wether sources are switched on/playing or not.

Any ideas?!?!?!? I'm after any suggestions on how i may troubleshoot/isolate/eliminate this issue.

Matt

 

Ok a first a few question .....
would you describe it as a hum or whistle .

How long have you heard it ?
what sort of area do you live in [rural or town ]?
If the pre amp is off do you still hear the sound?
Is the amp near the TV ?
Do any power cables run close to the preamp?
Is the preamp near the TV ?
Do you hear a difference to the sound at different times of the day?
Can you hear it whilst music is played at normal listening levels?
How old is the power amp ?


Look forward to your answers !

 

Wow: ok.

- How long have you heard it ?
Initially i didn't notice the sound, but this doesn't mean it wasn't always there! Certainly, prior to changing the preamp, it was hardly an issue. I'm wondering though, if the problem is new, or has been excarbated by the new preamp.

- what sort of area do you live in [rural or town ]?
City.

- If the pre amp is off do you still hear the sound?
No.

- Is the amp near the TV ?
Yes, i suppose it is. The TV has a cabinet beneath it with all the gear. The amp sits at the base of my stack. The preamp sits directly ontop of this, there are 2 sources on the shelf above that, then another source on the shelf above that, then the TV.

- Do any power cables run close to the preamp?
Not really, the cables from the sources above clear it due to the shelving.

- Is the preamp near the TV ?
See above. I think I see what your getting at hear. Perhaps the preamp should be moved off the amp? Certainly the setup isn't ideal, but space is at a premium until i spring for new (more suitable) AV shelving.

- Do you hear a difference to the sound at different times of the day?
Not really - certainly, it's more audible in the evening, but i believe this is due to lower ambient noise. ie. you can hear it better when it's quiet (obviously!)

- Can you hear it whilst music is played at normal listening levels?
Yes, during really quiet passages.

- How old is the power amp ?
Not sure.... Rotel 1080 power amp, at a guess i'd say ~4 years.

 

Id still say you've a earthing problem somewhere in system.

 

I have a hum between my pre and power amp which is quite noticeable on switch on, or if there's no music playing..
Not only that it's at the right frequency to be earth based (i.e. lowish rumble)..
It's definitely the pre-amp as it doesn't appear when I connect the cdp direct, but as it doesn't intrude on music, and it sounds so good I haven't done anything about it...

However, what I will do one day when I can be bothered, and may work in your case, is to see what happens when I touch a grounded wire to the various cases.. Might sort it!

 

I also agree with the above but suggest you move the stuffaway from the HT of the telly.

Do that as a start...just unpluging everthing and moving things arround can play a part !

When you have everything away from the tv[ inverse square law applies here]

You can then test for Hum and earth loops ....

Oh was it a hum or whistle ?

 

All defo earthing probs in my book, switching sources on completes the ground loop. To the original poster, Id take a close look at your pre, take the case off and have a look inside, you may well have a loose ground on a phono socket or something similar.

 

Defo good advice from zanash there. Im lucky that all my gear is tucked away at the back of the lounge. Ive also found that since changing to t-mobile I pick-up those dreaded noises if its too close.

 

If its a high pitched whistle, its not earthing, I have had earth probs. myself in the past and hate em with a vengence.

I have occassionally heard hi pitched whistles from cd players, not sure what this is, rf noise from the laser or perhaps ultrasonic noise from the dac, no idea really.

Or could be your amps oscillating which is VERY bad news for tweeters, eventually it will burn them out, but if its very faint, probably doens't matter.

 

Unplug everything in the room. Plug in the amp and preamp, any noise?

Plug in the CD player, and recheck.

I found that the noise in my system was caused by airbourne interference from my TV and Sky +. The only effective fix was to turn off everything but the system when listening.

Good luck
J

 

yep ...good advice

start from basics and work up......eliminate all the obvious causes.

That was my line of though asking about the sound ..if its not a 50hz hum I'd start to look for noisey caps or something else that not right with the pre

 

It could also be the driver electronics/transformers(??) for the fluoro display - my Sony MD deck does this when powered up. Well annoying...

 

Yep mine make a scratchy sort of sound, but he has this all the time.

 

I have a ground loop problem between my PC and Hifi. When all the grounds are connected to each other, the hum is there. Whenever all the grouds are manually dissconected itis still there. When I fit a ground loop isolator, it quietens ALOT.

How can there be a ground loop if i have dissonected the PC from the ground? I have manually cut the eatrthwire....

If anyone can suggest...please Don't Bother with the OMG that is so dangerous.....i don't care if it gets my hifi working wthout the buzz.

 

If you could answer the questions previously ask in this thread......

How long have you heard it ?
what sort of area do you live in [rural or town ]?
If the pre amp is off do you still hear the sound?
Is the amp near the TV ?
Do any power cables run close to the preamp?
Is the preamp near the TV ?
Do you hear a difference to the sound at different times of the day?
Can you hear it whilst music is played at normal listening levels?
How old is the power amp ?

But relavent to your kit...

Is the PC in the same room as the HIFI
are they connected to the same mains spur
which item do you feel is the problem
just because something is not connected to ground it can still have its own floating ground.

Have you tried grounding the pc case to the ground pin of the amp ?

 

I started hearing it when I removed my proccesor from the chain and plugged my pc straight into a stereo preamp then the power amps.

Town

no

5m

no

5m

I dont hear it at night when I am asleep

VERY loudly

5-6 years

comp is 3m from hifi

yes

I wish i knew

I will try that now.

 

Try running everything from the same mains plug ....yes yes I know.

As previously stated .......disconect everything signal wise

reconect amp and speakers only listen ......
then ad in each peice individually and see if you get hum
If your still looking you then need to add in the cd player and go through adding everthing else individually and then removing.

At some stage you will regenerate the hum ....

contact us when you have isolated the errant kit.

 

It's well worth trying a ('proper') mains filter. Depending on you mains wiring, for equipment with a floating chassis (most stuff) it's possible that the only time your (electical audio) signal sis actually referred to ground is in your mains distribution uint or even back at the nearest substation, allowing the network of earth connections to act as an aerial . A 'full' mains filter will provide a local reference to earth which can snub various rfi effects.

In terms of the effects you are describing, the key improvement in my system was to remove a faint background (audio) signal that could be heard through the centere speaker of my (linked) home cinema system when the surround amp was turned off (As well as a considerable improvement in the obverall sound quality of the system)

Worth a read here - ignore the cable review, just read the 1st bit on noise current loops