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PostPosted: Wed Nov 22, 2017 6:32 am 
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Joined: Mon Mar 12, 2007 5:12 am
Posts: 60
Location: Rawdon, QC, CA
I've had a totally rebuilt Scott 299B from a reputable vintage tech (Craig from NOSvalves) for the past 8 years. Initially it was setup in a living room driving Klipsch Fortés and has recently been moved to a dedicated listening room with some treatment and dedicated line driving Klipsch LaScalas. I had never noticed, in the previous setup, that there is a very subtle hum coming from the amp's main transformer which bleeds to the speakers. Of course in my first setup there was a lot of competing ambient noise coming from the house... fridge, lights, kids. My studio is almost absolutely quiet and to be fair, I can hear any electrical appliance humming in it.

I contacted Craig, who stands by his work for life, and he claims that there should be NO noise whatsoever coming from the speakers. I chose to bring it to a local shop in Montréal, l'Audiophonie which came highly recommended on CAM. They tested it and recommended I change the output tubes which I did. They put the amp through it's paces and it came back totally healthy, measuring exactly as the schematic intended, the tech even commented on Craig's work which he said was flawless. I brought the amp home and needless to say, the hum persists.

All of which brings me to my question... is it possible to have NO noise whatsoever, as Craig claims, or am I just hearing the normal noise floor of this particular amplifier? I have to say, in all honesty, that as soon as music is played, and try as I might, I cannot hear any hum. I should also mention that as far as the music is concerned, it is glorious and never fails to bring me deep pleasure, there is some magical synergy with the Scott and Heritage Klipsch.

Daniel


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PostPosted: Wed Nov 22, 2017 6:46 am 
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Joined: Tue Dec 07, 2004 4:18 pm
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Location: GTA, ON, CA
Perhaps the amp is not at fault but you have a ground loop problem. Does the "hum" increase as you increase the gain? Does the amp still hum through the speakers with no source connected?


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PostPosted: Wed Nov 22, 2017 6:51 am 
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Location: Rawdon, QC, CA
I should've mentioned that... no the hum doesn't increase with the gain, and it persists without any connected sources.


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PostPosted: Wed Nov 22, 2017 8:00 am 
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Joined: Tue Dec 07, 2004 4:18 pm
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Location: GTA, ON, CA
Was the stock 2-prong plug replaced with a 3-prong plug? If so, try a cheater plug to help isolate the problem.


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PostPosted: Wed Nov 22, 2017 9:53 am 
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Joined: Sun Dec 28, 2008 7:49 am
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Location: Fairport Beach (in Pickering), ON, CA
Have you tried going back to the Klipsch Fortes?

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Tom

Collecting vintage tube Pilot (Pilotone) HiFi gear.


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PostPosted: Wed Nov 22, 2017 10:18 am 
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Joined: Mon Mar 12, 2007 5:12 am
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Location: Rawdon, QC, CA
It is the stock 2 prong plug.

I have tried again with the Fortés and any sound it makes is drowned out by the room's ambient noise floor(?), only becoming apparent when I put my ears within a foot of the speakers, certainly not from the listening chair which explains why I had never heard it before.

We plugged it into speakers at L'Audiophonie (don't remember the make and model) with the owner and tech and they claimed it made less noise than their floor model tube amp.


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PostPosted: Wed Nov 22, 2017 10:46 am 
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Your speaker are highly sensitive, therefore, what you could be hearing is the tube rush at idle which is quite normal. Once the music starts playing, I assume that this becomes a non-issue. Also, I take if from your earlier post that you cannot hear the hum/hiss from your listening position, correct?


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PostPosted: Wed Nov 22, 2017 11:59 am 
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Location: Rawdon, QC, CA
It's not an issue when the music is playing, though I do hear it from my listening position without music.


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PostPosted: Wed Nov 22, 2017 12:33 pm 
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Joined: Sun Mar 18, 2007 2:01 pm
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Location: Calgary, AB, CA
Precautious D wrote:
It's not an issue when the music is playing, though I do hear it from my listening position without music.


First thing first you have to make sure that it is a humming noise, not the buzzing noise. A humming noise is a sinewave which basically constant noise and it caused by either ground loop or problem with the power supply. However, if it's a buzzing noise which sounds like a white noise with lots of harmonics chances are it's caused by either bad tubes or connections.

To get rid of the humming noise you can either do one of the two things that caused it. Restored the power supplies very expensive proposition and or traced the culprit of the ground loop issue cheaper proposition. If all else fails you may have to buy a new power amp.


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