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Old 26th February 2009, 06:35 PM   #1
jzono1 is offline jzono1  Norway
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Default Buzz. Grounding-related?

My "Darling" 6j4 / 1626 amp has some sort of buzz. I think it's a grounding problem.

For driving normal high-sensitivity speakers it's not a big problem, barely audible in my 96dB/W Voigt horns, but for driving headphones it's a showstopper.

The buzz varies in intensity with the volume knob. At max volume the buzz is low, at min volume it's very high. The volume knob is wired as a voltage divider.

The amp is grounded via a bus bar.

The hum is there even before I turn on both heaters and B+.

What could be wrong?
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Old 26th February 2009, 07:45 PM   #2
m6tt is offline m6tt  United States
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If it hums before the tubes fire up it's probably magnetic coupling between power transformer and output transformer. Try moving them around, or rotating one or the other by 90 degrees.
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Old 26th February 2009, 08:43 PM   #3
jzono1 is offline jzono1  Norway
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But how could it be magnetic coupling if it happens before the mains transformer gets any power?
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Old 27th February 2009, 01:01 AM   #4
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Default Re: Buzz. Grounding-related?

Quote:
Originally posted by jzono1
My "Darling" 6j4 / 1626 amp has some sort of buzz. I think it's a grounding problem.

The hum is there even before I turn on both heaters and B+.

What could be wrong?
Sorry this may come off sounding preachy but I only have a few minutes and want to give the most help I can.
There might not be anything wrong . . .

Hum and Buz are not the same thing . Which one is it? or is it both? Is it the same when powered and when not?

What other powered devices are close by ?

How is everything else powered ? (ie. all from the same socket?)

If there's hum with no power then something else is inducing or transmitting it. Look at the available powered (whether visible or not) sources. Remember that strong magnetic fields don't care about shelves unless they're magnetic /ferrous and will go right through to induce hum on the transformers of your amp if they can.
Play around, move things around. Unplug the amp - does it still hum? Take it into the kitchen etc etc.

Sorry , gotta go. Hope this is helpful .
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Old 27th February 2009, 07:33 AM   #5
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Try to connect 2 resistors 200 ohm serial. Middle point connect to
ground.../or to middle point of 2 serial con.resistors 200 kohm ang 20 kohm between PS and ground,....200 kohm to PS, 20 kohm to ground/.
Left and right point of this group connect to 6,3 v. /See that 6,3 v
not be connected to ground!!!/.
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Old 3rd March 2009, 09:49 PM   #6
jzono1 is offline jzono1  Norway
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Ok. It's definitively grounding-related.

Ran the amp from an ungrounded outlet, with a grounding wire out through the window onto the heap of snow outside. The buzz is gone, it's dead silent.

Suggestions on how to find out why it doesn't like the grounding in my house?
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Old 3rd March 2009, 10:36 PM   #7
Trout is offline Trout  United States
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Quote:
Originally posted by jzono1
Ok. It's definitively grounding-related.

Ran the amp from an ungrounded outlet, with a grounding wire out through the window onto the heap of snow outside. The buzz is gone, it's dead silent.

Suggestions on how to find out why it doesn't like the grounding in my house?
Our AC in my area is very dirty.

You might need a power conditioner, I have several outlets in my guitar room that are very noisy. I put in a Furman conditioner and fixed it right up.

Perhaps you should also get a good outlet checker, I have seen a heck of a lot of mis-wired outlets out on building inspections even in new construction.
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Old 3rd March 2009, 11:35 PM   #8
jzono1 is offline jzono1  Norway
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It's hard to miswire outlets in Norway. Here we got balanced mains, -115v & 115v + ground.

Could the ground itself be dirty?
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Old 4th March 2009, 12:44 AM   #9
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You have balanced power lines? Norway is cool!

Quote:
Originally posted by jzono1

Suggestions on how to find out why it doesn't like the grounding in my house?
You haven't said what other devices you're using connected to the Darling and whether they were all plugged into the same power outlet (via a power bar).
When you tried the ungrounded socket did you also check for hum before grounding to the snow? Maybe just lifting the ground is what stopped it.
When you grounded to the snow did you have your music source/player connected?
Are the interconnects good?
If it were me I'd even measure the resistance from the wall socket's ground pin connection to the snow ground I.O.W. - Are you sure that the socket/house wiring ground connections are good?

Tried measuring voltages between chassis ? AC current between source output and amp input rca grounds ?(with interconnect disconnected)

From several thousand miles away and with no details of what you've tried so far the best support I can think of is to suspect and try everything in the chain . . . systematically.
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Old 4th March 2009, 03:17 AM   #10
jzono1 is offline jzono1  Norway
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Oh, right - for these tests I used a battery powered iphone as the source.

Just connecting to ungrounded socket gave the same buzz, once i grounded it to the snow it went silent.
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