OT: Transformer hum

Arno van der Heijden · January 20, 2005, 03:32:58 PM

I recently bought a used Kitty Hawk Quattro 19" preamp. However, it hums very badly and I'm trying to get rid of this with the help of the info on Geofex.

Now I was wondering, I noticed the power transformer exhibiting an audible mechanical hum. Could this be coupled into the circuit one way or another, causing electrical hum?

Paul Marossy · January 20, 2005, 05:45:59 PM

Does this thing have an internal transformer? Sometimes those wall warts with no ground prong makes these effects/preamp/whatever units have an annoying hum. At least on my Zoom 9030 that was the case. :evil:

Arno van der Heijden · January 20, 2005, 05:55:52 PM

Yep, it has an internal transformer.
Btw, I just found out that part of the hum goes away when I put my hand on the housing. Is this is a mechanical or electrical thing? In other words, is this because it stops the housing from vibrating (induced by the transformer) or because of some kind of grounding thing?

Paul Marossy · January 20, 2005, 06:03:34 PM

Does it have a grounded power cord? In my experience, usually if the hum stops when you touch the enclosure, it's somehow related to grounding.

R.G. · January 20, 2005, 11:26:14 PM

Two points to Paul.

Paul Marossy · January 20, 2005, 11:30:23 PM

QuoteTwo points to Paul.

Yeah!! :wink:

Seriously though, I wonder just why do some of these companies design things with these Mickey Mouse power supplies?! :x

Arno van der Heijden · January 21, 2005, 06:27:30 AM

Yep, it has a grounded power cord.

I just did some more tests. The hum only becomes less if I put my entire hand firmly on top of the housing. Not if just touch it with a couple fingers. I suspect this dampens the mechanical vibration of the housing.

Also, the high gain channel suffers from oscillation. I can also stop this squeel by putting my hand on the housing. :?

H.Manback · January 21, 2005, 09:15:39 AM

Try putting a heavy book on it or at least something that will put pressure on it and not ground the thing.

Also you can try taking a piece of electrical wire and put one end on the enclosure and the other one on a earth point you are sure is connected. Are you sure that your wall outlet is actually connected to earth (just because the wall outlet has a earth pole doesn't mean it is actually connected of course)?

Paul Marossy · January 21, 2005, 10:10:36 AM

QuoteAlso you can try taking a piece of electrical wire and put one end on the enclosure and the other one on a earth point you are sure is connected.

That's what I ended up doing with my Zoom 9030 - grounding the enclosure. It made a world of difference.

QuoteAre you sure that your wall outlet is actually connected to earth (just because the wall outlet has a earth pole doesn't mean it is actually connected of course)?

Very good point.

Arno van der Heijden · January 23, 2005, 06:51:17 PM

Thanks for all the suggestions.

I tried and tried again and the problem turned out to be the wall outlet. The problem is only present when I use a wall outlet that is not connected to earth.
It is remarkable that this also stops the high gain channel from squeeling.

Torchy · January 23, 2005, 07:09:16 PM

crp

Paul Marossy · January 23, 2005, 07:32:55 PM

QuoteIt is remarkable that this also stops the high gain channel from squeeling.

Sometimes that cycling of a power supply can cause your circuit to oscillate. I had that problem with my Boss Metal Zone whenever I used my wah with it. It turned out that the wah was picking up induced hum from the power supply wall wart and that in turn caused my Metal Zone to start squealing like a pig trying to avoid slaughter! I moved the wall wart to the other side of the pedalboard from the wah and it stopped doing that! Weird, I know. :?

QuoteWhy would you have a mains outlet that ISNT earthed ?

Unfortunately, there are lots of places in the world with bad electrical wiring, especially in the older areas. Even in the U.S., there are still places like this. :shock:

Arno van der Heijden · January 24, 2005, 04:05:00 AM

Quote from: Torchy:shock: Why would you have a mains outlet that ISNT earthed ?

Because the house I live in is over 30 years old. At that time, this wasn't obliged in the Netherlands, so half of the outlets in the house are earthed, the other half aren't.

Torchy · January 24, 2005, 08:49:47 AM

crp

Paul Marossy · January 24, 2005, 10:22:39 AM

QuoteBecause the house I live in is over 30 years old. At that time, this wasn't obliged in the Netherlands, so half of the outlets in the house are earthed, the other half aren't.

You really ought to get all of those receptacle circuits grounded! :shock:

H.Manback · January 24, 2005, 08:32:21 PM

Ahh, safety schmafety, I'm from the Netherlands as well, and it is actually pretty rare to have a house that has only grounded wall outlets. Only kitchen/bathroom and washing machine stuff like that are connected to earth, and I don't read "Man (or woman) electrocuted by electrical appliance" every day.

Of course I see the necessity of safe wall outlets, but it's not as bad as it looks

puretube · January 25, 2005, 02:45:26 AM

Quote from: TorchyAh, sorry, I see - in the UK all properties (whatever the age) are subject to very strict IEEE wiring regs. Your unearthed outlets would be illegal here.

same here in Germany: the power company`d shut the power down until every outlet got 3 connexions...
(230...240V here, too).

(what you do after the outlet, is your thing...)

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OT: Transformer hum