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 Post subject: Experience with hum
PostPosted: 16 Nov 2010, 09:45 
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Joined: 23 Jul 2010, 18:23
Posts: 23
My K12 g has hummed since I built it and I think that it is fixed now.

The hum increased only slightly when the volume increased. Mark Houston pointed out that I had used a thin piece of aluminum to mount the transformers and I think that has contributed to resonating hum/buzz. I resoldered several questionable connections; retwisted the trans wires; used a ground loop isolator - no improvement.

I measured as described in this post on Decware:
Quote:
Hum is a 60 cycle (50 cycles in other countries) tone that lives in the noise floor of all audio gear or when problematic, becomes the noise floor. Hum can be measured at the output of any amplifier with a decent AC volt/ohm meter. The procedure is simple; Just hook your speakers up to the amp, remove the input cables from the amp, turn the gain knob (if it has one) all the way down. With your meter connected across one channels output jacks (with the speaker hooked up at the same time) your meter should slowly drop to below 2 milivolts AC. (All of our amplifiers fall below this value.)

The amp measured OK.

So, I cleaned the pins on the tubes with contact cleaner and a scotch brite pad. The right channel seems dead quiet; the left has some hum and I will clean those pins again. I also added a sorbothane noise pad under the amp.

Hope this helps someone else.

-- Chuck


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 Post subject: Re: Experience with hum
PostPosted: 18 Nov 2010, 12:52 
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Joined: 23 Jul 2010, 18:23
Posts: 23
Well -

I guess I did not get rid of all of the hum. The hum is only in the left channel now. I am not sure if it came back or if I just did not listen closely enough before. I swapped the left and right sets of tubes and still had left channel hum.

-- Chuck


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 Post subject: Re: Experience with hum
PostPosted: 19 Nov 2010, 13:34 
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Joined: 28 May 2008, 21:53
Posts: 4579
Location: Winnipeg, CANADA
Hi Chuck,

Can you post a link to the Decware thread, it sounds like a good read.

If you are getting more hum in one channel than the other, it is likely got to do with the physical layout. I'll bet that the input or output of left channel is closer to the AC mains power or the AC secondary from the power transformer than the right channel.

On my K-12M tube amp kit I had more hum in the left channel for this reason.

Post of a photo and lets see if there is something simple than can be changed.
Cheers

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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 Post subject: Re: Experience with hum
PostPosted: 19 Nov 2010, 18:58 
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Joined: 23 Jul 2010, 18:23
Posts: 23
Gio -

I assume that the problem is with the layout as you describe. The side that is louder is nearer the power transformer. Pictures are posted on page 8 in the thread "Newbie checking in, K-12G pics." I was lazy and didn't post pics here.

-- Chuck


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 Post subject: Re: Experience with hum
PostPosted: 23 Nov 2010, 13:41 
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Joined: 28 May 2008, 21:53
Posts: 4579
Location: Winnipeg, CANADA
The problem may be the power switch which is close to the signal input. When you cleaned up the wiring, did you use a twisted cable for the switch wiring?

You can experiment by disconnecting the switch from the chassis and physically moving it away from the input to see if that make a difference. If that is the source of the problem you could move the switch towards the rear of the chassis. Proceed with caution when doing this. :!:
Cheers

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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