Hum

Frizzy brizzy

Wammer
Wammer
Feb 3, 2013
656
5
0
New forest
AKA
Laurie
HiFi Trade?
  1. No
Hi folks,

just took delivery of art audio Carissa , sounds fab, big bold present and subtle, and that radio 4.

bit of a bug though, there is a low level hum on all channels at a constant volume and tone. Having emailed falcoron he explained it to be pre amp picky,and this is source of earth hum issues. It's not a big enough noise to preclude listening, but I do of course want rid of it.

Without having to change pre amp as now very skint, the Berning is a Joy, a mc stage of great beauty, any ideas to cure the problem. All signal wiring is kondo , power cords are tellurium q black. On separate spur run from its own box with jps inwall shielded cable. Never had hum issue before, so only variable is the Carrisa , help required, would hooking up a earth spike I have on garden. Not sure if the ground impedance is less via spike, must check when light.

thanks to all tech minded for ideas.

laurie

 

Valvebloke

Member
Wammer
Dec 3, 2009
4,432
274
128
Didcot, Oxon
AKA
Graeme
HiFi Trade?
  1. No
First thing is to confirm where the hum is coming from. It might be the pre. But it might not. So unplug, at the pre end, the interconnects that take the signal from the pre to the power. Short the signal terminal to the ground one on each interconnect (if they're RCAs this is done most easily by wrapping the whole lot in a bit of tinfoil and squeezing it down tight so it connects both terminals together. Turn on the amp. Does it still hum ? If yes then the hum's coming from inside the amp. If not then it's coming from further back - pre or ground loop somewhere.

VB

 

falcoron

Wammer
Wammer Plus
Jan 17, 2006
4,409
150
143
Belfast, , United Ki
AKA
RON
When i had the carissa with an AN M2 it hummed quite a bit, less so with the ART VPS pre amp and virtually silent with the Graaf pre. I had several pre amps at home when doing my shootout and some of those intrduced a lot of hum as well, so maybe the pre i dont know. the amp was serviced with nothing showing up on the test bench of the service engneer.

Also my systems speakers are around 105db so very suseptable to background noise. Only the AN M2 pre was too much to bare others had a slight noise but never annoyed. The amp does have massive transformers though but i dont know if that makes a difference. Hum as far as i know can be caused by a lot of different things, my speakers would hum like mad some nights and with taxi or radio voices in the mix as well, some nights were really bad. i was told to get some RFI filter devices so bought some for computer cables the just clipped onto my interconnects and speaker wires that totally illiminated the interferance for me, i have these permently on the wires now.

Tom Willis is the man to speak to. He will know what to try.

Laurie i pm'd his telephone number to you mate.

 

hermit

Wammer
Wammer
May 9, 2013
423
13
48
Glasgow
AKA
Paul
Maybe the preamp has too much gain for the power amp. A pair of Rothwell attenuators inserted into the power amp may well reduce the noise floor

 

falcoron

Wammer
Wammer Plus
Jan 17, 2006
4,409
150
143
Belfast, , United Ki
AKA
RON
Maybe the preamp has too much gain for the power amp. A pair of Rothwell attenuators inserted into the power amp may well reduce the noise floor
That was certainly the case with the AN pre as the gain was way to high, but the ART pre is made to match so gain would have been perfect and it had a hi low gain feature, it hummed but was very very slight and you had to get your ear up close to the drivers to hear it. the Graaf was silent as the Grave. Was the best sounding to I had a hovland as well and it hummed a bit but again very slight. Changing interconnects to sheilded helped a little but the RFI bits i added helped with interference i would get from time to time.

I found attenuators killed the gravitas of everything i tried them with.

 
G

Guest

Guest
Tom Willis is the man to speak to. He will know what to try.

Laurie i pm'd his telephone number to you mate.
+1

Tom is a really helpful guy and will be able to sort your problem.

 

Frizzy brizzy

Wammer
Wammer
Feb 3, 2013
656
5
0
New forest
AKA
Laurie
HiFi Trade?
  1. No
Thanks dudes as said not too loud , music is fine, audible but not pervasive.

No hum from berning pre, as tried. With Berning power dead quiet, and has built in attenuation. Though I should try cd direct to compare.

I am leaning towards position/ shielding those huge transformers, sometimes distance helps, maybe longer RCA , or move mains outlets , cords.

 

clap

Wammer
Wammer
Sep 26, 2009
1,544
34
78
Wales
AKA
tristan
First thing is to confirm where the hum is coming from. It might be the pre. But it might not. So unplug, at the pre end, the interconnects that take the signal from the pre to the power. Short the signal terminal to the ground one on each interconnect (if they're RCAs this is done most easily by wrapping the whole lot in a bit of tinfoil and squeezing it down tight so it connects both terminals together. Turn on the amp. Does it still hum ? If yes then the hum's coming from inside the amp. If not then it's coming from further back - pre or ground loop somewhere.VB
Can I just clarify this? Unconeect the pre to power interconnects at the pre end, leave attached to the power amp. Can you then just touch the 2 ends together whilst still plugged into the power amp? do you need the tin foil? Does the tin foil short the grounds attached to the shell? Is that it? Could you just touch pins and shells together?

I don't want to fuse my power amp!

 

Frizzy brizzy

Wammer
Wammer
Feb 3, 2013
656
5
0
New forest
AKA
Laurie
HiFi Trade?
  1. No
Will wait till I have spoken to Tom willis before I try anything, Ron kindly gave me his number. I doubt very much it's the Carissa , prob a loop or shielding issue, or amp compatibility, I'm just not tecky enough to work it out.

cheers all.

- - - Updated - - -

Ps Ron , good photo.

 

Valvebloke

Member
Wammer
Dec 3, 2009
4,432
274
128
Didcot, Oxon
AKA
Graeme
HiFi Trade?
  1. No
Can I just clarify this? Unconeect the pre to power interconnects at the pre end, leave attached to the power amp.
Yes.

Can you then just touch the 2 ends together whilst still plugged into the power amp?
Not sure I understand the question. The now disconnected end of each cable will have two terminals - a 'signal' one and a 'ground' one. In the case of RCA/phono connectors the central pin is the the signal terminal and the outer cylindrical one, almost always connected to the shell, is the ground terminal. What you want to do is to electrically connect the signal terminal of each cable to its ground terminal in the shortest, most direct way possible.

do you need the tin foil?
You need some sort of electrical conductor. Tinfoil is a good conductor and is easy to scrunch over the end of an RCA/phono plug to make good contact between the central pin and the grounded shell. But you could use a piece of wire if you had one. You'd have to find a way of twisting it round the central pin and the grounded shell and making it stay there. But if you could arrange that it would work just as well as tinfoil.

Does the tin foil short the grounds attached to the shell? Is that it?
It shorts the grounded shell to the central pin.

Could you just touch pins and shells together?
An RCA/phono plug is pretty rigid. So in practice you won't be able to bend the central pin sufficiently to touch its own shell, and if you did the plug would probably be damaged beyond repair in the process. You could touch the pin of one plug to the shell of the other one, and vice versa. But this would not be such a good test. Now you would have generated a ground loop, of a sort, between the two channels and this might cause hum of its own which would confuse the situation. I guess if you did this and got no hum you could be pretty sure there was no problem with the amp. But if you did hear hum you wouldn't know if it was the amp or the funny ground loop that was causing it.

I don't want to fuse my power amp!
These are signal leads that we are talking about. There are no fuses involved. Of course you should do all this fiddling with the amp powered off. When you are happy that you have shorted the signal terminal to the ground terminal then, and only then, should you turn the amp power on. Then listen for hum. The turn the amp off and restore the wiring to how it was originally.

EDIT: Remember though, I am just a bloke on the internet. If you aren't clear about the procedure then feel free to ask some more. But don't mess with expensive fragile things if you're not happy that you understand what you're doing.

EDIT II: A quick Google shows that the Classe 10 has balanced inputs as well as regular unbalanced ones. The above instructions are for regular unbalanced inputs. If you want to short balanced inputs then you need to connect signal positive to signal negative.

VB

 

clap

Wammer
Wammer
Sep 26, 2009
1,544
34
78
Wales
AKA
tristan
Yes.Not sure I understand the question. The now disconnected end of each cable will have two terminals - a 'signal' one and a 'ground' one. In the case of RCA/phono connectors the central pin is the the signal terminal and the outer cylindrical one, almost always connected to the shell, is the ground terminal. What you want to do is to electrically connect the signal terminal of each cable to its ground terminal in the shortest, most direct way possible.

You need some sort of electrical conductor. Tinfoil is a good conductor and is easy to scrunch over the end of an RCA/phono plug to make good contact between the central pin and the grounded shell. But you could use a piece of wire if you had one. You'd have to find a way of twisting it round the central pin and the grounded shell and making it stay there. But if you could arrange that it would work just as well as tinfoil.

It shorts the grounded shell to the central pin.

An RCA/phono plug is pretty rigid. So in practice you won't be able to bend the central pin sufficiently to touch its own shell, and if you did the plug would probably be damaged beyond repair in the process. You could touch the pin of one plug to the shell of the other one, and vice versa. But this would not be such a good test. Now you would have generated a ground loop, of a sort, between the two channels and this might cause hum of its own which would confuse the situation. I guess if you did this and got no hum you could be pretty sure there was no problem with the amp. But if you did hear hum you wouldn't know if it was the amp or the funny ground loop that was causing it.

These are signal leads that we are talking about. There are no fuses involved. Of course you should do all this fiddling with the amp powered off. When you are happy that you have shorted the signal terminal to the ground terminal then, and only then, should you turn the amp power on. Then listen for hum. The turn the amp off and restore the wiring to how it was originally.

EDIT: Remember though, I am just a bloke on the internet. If you aren't clear about the procedure then feel free to ask some more. But don't mess with expensive fragile things if you're not happy that you understand what you're doing.

VB
Your more than just a bloke on the internet to me ;-) .

 

Forum statistics

Threads
113,444
Messages
2,451,263
Members
70,783
Latest member
reg66

Today's Birthdays

Latest Articles

Wammers Online