Valve amp huming

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Rick_F
Schaut ab und zu mal vorbei
#1 erstellt: 18. Nov 2003, 13:10
First of all I would like to say hello to everyone as this is my first posting

I have recently obtained my first valve amplifier. Its a Grant G100 Pre-amp, paired with Grant G200 monoblocks. My problem is since I got them home from where I auditioned them. I have a pretty loud mains hum that I just can't seem to clear. They were fine at the audition house so I know it must be either the journey home or my set up that's creating it.
It only happens when the pre-amp and monoblocks are fully switched on (regardless wheather any components connected to pre-smp or not). If I turn the pre-amp off the hum goes, so doubt its the monoblocks. Its not the interconnects or power cables or even the mains filter (Isotek Mini Sub) as I've taken them out the equation.
I wonder if it could be either something in the pre-amp being dislodged (have removed and cleaned all tubes in there, tested earthing) or I need to remove the earth lead from the monoblocks and relying on the interconnects to earth them via the pre-amp. But I don't like that idea as sounds dangous to me if I forget and disconnect the interconnects.
Any advice or ideas wold be greatfully received so I can start to fully enjoy these monsters!
Manek
Inventar
#2 erstellt: 18. Nov 2003, 13:21
hum's are usually power related....or a dry solder.
check the wall socket thoroughly.....if the wire coming into the wall socket is a series connection from another socket in which another device with a motor or compressor is connected there could be a hum.

Have you tried connecting the pre-amp to an entirely different wall socket...maybe on a line where only your lights are connected ? do you have tube lights at home ? maybe a bad choke could be the culprit...

Take the preamp to your neighbours house and check it out if all else fails....

Let me know....
Manek
Inventar
#3 erstellt: 18. Nov 2003, 13:30
by the way...a slight hum of 1mV to 2mV is common on valve amps...and this much hum should not affect sound quality...
Rick_F
Schaut ab und zu mal vorbei
#4 erstellt: 18. Nov 2003, 13:31
Hi Manek,

Yes I've tried switching mains outlets without luck. I have Naim amps which never had a problem in the room and you probably know what they are like for finding and enhancing hum!
I do intend to take the pre-amp to a friends place and put it in his system towards the end of this week.

I'll let youknow if I do find a cure!

Rick.
Manek
Inventar
#5 erstellt: 18. Nov 2003, 13:36
Some tips from affordable audio web site on huming valves.

http://www.affordable-audio.co.uk/Amplifier%20Tips.html
kimber-frank
Stammgast
#6 erstellt: 18. Nov 2003, 19:05
Hey!
Many amps make a noise, for example marantz pm7000 or pm8000 have a slight huming. But if you listen to music, you won't hear it.

So how loud is it? Can you hear the huming while your music is playing?
Rick_F
Schaut ab und zu mal vorbei
#7 erstellt: 18. Nov 2003, 23:27
Yes I'm aware of back ground noise, but this hum is pretty loud! It requires quite a bit of volume to drown it out, and can still be heard easily when trying to listen to a more quiter, slower paced song.
sledgehammer
Stammgast
#8 erstellt: 19. Nov 2003, 20:35
if its really loud - a it looks like - take it back to your dealer.
Manek
Inventar
#9 erstellt: 20. Nov 2003, 07:32
yup...back to the dealer it is once you try it at your neighbours house and the humm still exists...
Rick_F
Schaut ab und zu mal vorbei
#10 erstellt: 25. Nov 2003, 01:30
Thanks for all the advice. I've managed to track the hum down to the Pre-amp. It looks like part of the power supply is playing up. I have a friend working on it as we speak
Manek
Inventar
#11 erstellt: 25. Nov 2003, 06:19
cool...let us know when its up and running again....
sledgehammer
Stammgast
#12 erstellt: 27. Nov 2003, 09:05
any results yet?
Manek
Inventar
#13 erstellt: 02. Dez 2003, 08:07
yeah....how is it now ?
LIPZ
Neuling
#14 erstellt: 08. Jan 2004, 15:00
Hi Rick

The hum you describe maybe down to a earth loop.As all 3 of the units will be individually earthed, try earthing just the pre-amp and remove the mains earthing from the power amp mains leads, thus using the interconnect as the earth for the p amps
sledgehammer
Stammgast
#15 erstellt: 09. Jan 2004, 07:25
that possible too! rick do you have any results?
Rick_F
Schaut ab und zu mal vorbei
#16 erstellt: 11. Jan 2004, 16:47
Hi, sorry for the very long delay in replying.

I did eventually manage to cure the humm by disconnecting the earth wire on each monoblock mains cable.
Have to say they sounded much better without the mains noise!

Thanks to everyone for taking their time to advice me on the problem
jon_koucky
Neuling
#17 erstellt: 04. Jun 2007, 16:31
Do you have a schematic for the Grant G200's? I have been looking for one for years!
bombaywalla
Stammgast
#18 erstellt: 07. Jun 2007, 14:21

Rick_F schrieb:
Hi, sorry for the very long delay in replying.

I did eventually manage to cure the humm by disconnecting the earth wire on each monoblock mains cable.

Bad boy! very bad boy for doing this!
you might have solved you hum issue but you have created an electrical hazard in your house!
God forbid that your grounding thru the interconnect cables malfunctions, you could electrocute yourself when you touch the amp chassis. You obviously know that the plate voltages of the output tubes are 400V or so!
ALso, if you have an electrical fire & the insurance company discovers that you were running your amps without a ground pin, you will get ZERO insurance money!
You are skating on thin ice!
DON'T DO IT! put that earth pin back & solve your issue at the root cause.

It seems to me that you have a ground loop (confirmed by you by removing the earth pin in your power amps) which means that you have different ground potentials that vary by a few mV in your different pieces of electronics. it is also very possible that you have DC in your AC supply. See if you can measure this using a voltmeter set to measure DC. Tube amps are more sensitive to DC in the AC due to the use of xformers.

One device that can help you is:
http://www.cablestogo.com/product.asp?cat%5Fid=3110&sku=41147

Another product:
http://www.graniteaudio.com/zero/index.html

Plinius Audio installs a ground lift switch in their amps that just breaks the ground connection to the electrical ckt WITHOUT breaking the ground to the chassis. If you do not want to use a ground loop eliminator, then install a ground lift switch.
sivat
Stammgast
#19 erstellt: 08. Jun 2007, 07:55
Line & Neutral might be connected "ulta" in your wall socket...plz have it checked with a well qualified and professional electritian.

Don't rely on those guys who check earthing with a electric bulb !!!

Regards
Siva.
Amp_Nut
Inventar
#20 erstellt: 08. Jun 2007, 08:03
Siva,

You are SO CORRECT.

Most of the earth Loop problems are due to in-consistent Line and Neutral problems.

Instead of a simple wire check & swap (the correct cure ), the ground is often 'lifted' as a quick and dirty cure

Anyways.... the Ground was 'lifted' in 2003 !

That is why I did not post on the tread now... which was resurected by someone looking for a Ckt diag ...
Suche:
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