What causes hum ?

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xcpointx
Junior tube assistant
Posts: 9
(2/13/04 7:21 am)
  What causes hum ?
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 I'm getting noticeable (read obtrusive) 100Hz hum (Im on 240Vac) when my tube rack preamp (Carvin Quad X) is played at stage volume.

Is there anything I can look into to clear this up?

The hum is there, guitar plugged in or nut, and I've tried changing all 9 tubes in various positions.



Edited by: xcpointx at: 2/16/04 2:20 am
 
ganzonimx
Hey get your own solder
Posts: 378
(2/13/04 7:59 pm)
 Re: What causes hum in a pre-amp
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 generally hum at the double frequency of the AC cycle comes from the power supply, worn out filter caps, bad grounding, ground loops. Have a look at the Tube Amp Debug Pages at geofex.com

How old is your amp and since when does it hum?

Cris
 
xcpointx
Junior tube assistant
Posts: 10
(2/14/04 5:02 pm)
 amp age
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 I just got the amp a few days ago.. its only a preamp with 12ax7 tubes and from 92/93.

It has run on 110V its whole life until now when Ive switched the power supply over to use 240V.

Where would I find the filter caps and how would I know if they are worn out?

your help would be appreciated!

Edited by: xcpointx at: 2/16/04 2:17 am
 
ganzonimx
Hey get your own solder
Posts: 383
(2/16/04 10:52 am)
 Re: amp age
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 Sorry I don't understand you, do you ask how to identify the caps inside the amp ore do you sake where to buy them?

By the way, is this amp a PCB amp ore point to point, do you have a schematic?
 
xcpointx
Junior tube assistant
Posts: 11
(2/17/04 2:12 am)
 Re: amp age
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 no, its PCB...

I wanted to know how to identify the filter caps. Someone has told me I must add an extra 330Mf cap into the circuit...?

Schematics for it are in PDF format here:

www.crossingpoint.za.net/quadx

Edited by: xcpointx at: 2/17/04 2:17 am
 
ganzonimx
Hey get your own solder
Posts: 389
(2/17/04 8:57 am)
 Re: amp age
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 Well I think this is a very complex hybrid amp, probably you could mess easy something up if you don't no exactly what you are doing. It might be better to bring in this amp to a Carvin service center to check it...

Cris
 
6G6
Junior tube assistant
Posts: 82
(2/17/04 9:26 am)
 Re: amp age
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 I just looked at all the schematics for that and I'd have to agree with what Cris said.
 
xcpointx
Junior tube assistant
Posts: 12
(2/17/04 10:29 am)
 Re: amp age
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 darn, Ive just imported it here to South Africa from the US... there is no way i will send it back there for service! Besides, they have actually discontinued their support for it cos it is an old product.

thanks for all your help so far.

If you have any ideas, please shout.


 
ganzonimx
Hey get your own solder
Posts: 390
(2/17/04 12:02 pm)
 Re: amp age
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 I'm not a navigator in electronics and neither a engineer, but I realized in life, if you go systematical into a new field, with plenty of patience and without the expectation that you will get results in short time, the human mind can rediscover everything a other human brain has yet discovered ore created once. As there is a waty in, there is always a way out of the jungle.

I would advice you first to read tree times the library of information, the link is on top of the page, then go trough the part catalog of Doug's shop and have a god look to all parts he sells. After that you should be able to identify all parts inside the amp.

Then try to identify and find all part from the layout inside the amp. Thats a long way to go, but it will help you to understand what's going on inside and eventually you stumble over something that explains the hum.

Stay tuned here in the forum and follow all threads, by the time that will pass you'll pick up a lot of things that opens your mind to amplifiers and their problems.

Cris
 
Leevi
Junior tube assistant
Posts: 105
(2/17/04 12:58 pm)
 Re: amp age
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 I would open it, switch it on and then press the printed board/and components in different positions with an isolated stick. If the hum changes you probably have a bad contact somewhere. Try to find the block that causes the hum. A PCB amp (especially with tubes) doesn't last as long as a point-to-point amp.
/Leevi
 
 
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