Tech: Stereo hum

Subject: RE: Tech: Stereo hum
From: open mike
Date: 24 Feb 06 - 12:32 PM

yep--sounded like a grounding problem to me..
i recenl.ty had a satellite dish installed and
the installer would not put it in unless i had
an adequate ground rod..so we proceeded to get
a copper rod from the hardware store and pound
it 8 feet into the ground..the wire is not strong
enough to withstand pounding directly so i had
to start the proceedure by taking another heavier
rod and making a hole, then shield the rod with
a larger diameter pipe until it was nearly level
with the ground. Glad you found the solution for
your hum.... now go learn the words!

Subject: RE: Tech: Stereo hum
From: kendall
Date: 24 Feb 06 - 09:46 AM

It's strange to me that it only hummed when the phono was on.

Anyway, thanks to all of you for helping on this.

Subject: RE: Tech: Stereo hum
From:
Date: 24 Feb 06 - 08:28 AM

Kendall, that proves the point. You had two "unconnected" grounds. Assuming the turntable was properly polarized, it means that either the outlet where the turntable was connected to, or the amp was connected to, was at a different potential.

What this creates is something called a ground loop. The reason why some of those people mentioned a third wire, is to eliminate that situation. If your turntable had the ground attached directly to the amp, it would have done the same thing.

Subject: RE: Tech: Stereo hum
From: kendall
Date: 24 Feb 06 - 08:19 AM

Well folks, you are not going to believe this. Having tried everything I could think of, and checking out some of the suggestions from you all, I disconnected the ground wire from the amp and the hum went away. Now, the whole system has no ground, and no hum.

Fascinating.

Subject: RE: Tech: Stereo hum
From: Paul Burke
Date: 24 Feb 06 - 03:24 AM

That's our advantage here in the UK. Unless you are relly out in the sticks, the earth is taken to ground at the substation, and the earth and neutral are connected where the feed enters the house.

I don't see how you can smooth 60Hz AC at 100A with a capacitor.

Subject: RE: Tech: Stereo hum
From: The Fooles Troupe
Date: 24 Feb 06 - 02:17 AM

When I bought my house I had the electrician add some power points. he was concerned cause the earth seemed problematical - it was connected to the water pipe feed from the street. What we didn't realise was that some clever turkey had replace d the feed-line with plastic water pipe - an inch of water pipe is not considered a good ground, so he added a new earth stake along with the ELCB.

I refrained from mentioning the smoothing capacitors, as that game is not for inexperienced amateurs.

Subject: RE: Tech: Stereo hum
From: Bert
Date: 23 Feb 06 - 07:19 PM

but now that they are all polarized you can't do that...

...replace the plug or file that prong down.

Does your stereo have a ground pin on the plug?

If so check that you house is grounded correctly. Lots of times ground wires get corroded and nobody cares until the stereo starts acting up. Go to your breaker box and follow the ground lead from there to the actual ground which may be a water pipe or a rod buried in the ground. Check all connections and replace any that are corrioded.

Make sure that all equipment that is connected to the stereo is correctly grounded and goes to the one ground.

Or you might need to relace the smoothing capacitors in your power supply.

Subject: RE: Tech: Stereo hum
From: Stilly River Sage
Date: 23 Feb 06 - 07:06 PM

It looks like its battery operated.

Subject: RE: Tech: Stereo hum
From: bobad
Date: 23 Feb 06 - 12:25 PM

You may want to try one of these http://www.radioshack.com/sm-see-all-needs-and-wants--pi-2062214.html.

If it doesn't work you can always bring it back.

Subject: RE: Tech: Stereo hum
From: Paul Burke
Date: 23 Feb 06 - 10:55 AM

Another thought- it could be the positioning of the turntable wrt the other components- the transformers can give out a hefty external 50Hz magnetic field. Trey a bit of sheng phooey on it.

Subject: RE: Tech: Stereo hum
From: JohnB
Date: 23 Feb 06 - 10:43 AM

Both of my setups have what someone described earlier. You have a ground wire coming from the turntable, which you connect to the a screw marked "ground" on the back of the amplifier (where all the other wires go in and out.
JohnB

Subject: RE: Tech: Stereo hum
From: Stilly River Sage
Date: 23 Feb 06 - 10:21 AM

I have exactly the same problem. I set up my sound system with lots of devices going into the amplifier. I finally figured out that the hum has to do with the turntable.

SRS

Subject: RE: Tech: Stereo hum
From: Paul Burke
Date: 23 Feb 06 - 10:15 AM

Are the leads the concentric type with a single pin in the middle, or do they have separate little pins?

Subject: RE: Tech: Stereo hum
From: gnomad
Date: 23 Feb 06 - 10:12 AM

When you say the TT is not on I'm assuming you mean that it is connected to power, but not in use? If so, is there a third lead from the turntable, in addition to the left & right channels?

My own TT has such a lead which connects to a dedicated earth terminal on the amp. On one of my amps disconnection makes no difference, but on the other one disconnecting produces a hum, while a loose connection gives hum + crackle.

Of course if there's no 3rd lead, or no earth terminal, this is no help, in which case sorry, no idea!

Subject: RE: Tech: Stereo hum
From: kendall
Date: 23 Feb 06 - 09:39 AM

A screen connection? and that is?

I once cured this in an old system by reversing the power plug, but now that they are all polarized you can't do that. Besides, it hums as soon as I turn it on.

Subject: RE: Tech: Stereo hum
From: Paul Burke
Date: 23 Feb 06 - 08:01 AM

Could be an earth loop somewhere- I once cured a friend's system using a nail- clipper- I just cut through one of the screen connections, and the hum disappeared magically. He viewed me as a combination of Einstein and Brunel for quite some time after.

Subject: RE: Tech: Stereo hum
From: The Fooles Troupe
Date: 23 Feb 06 - 07:55 AM

Beat me to it - is it a valve or a transistor, or even a more modern 'Integrated circuit based' type?

The gain is highest for the phono input, so any stray electric fields are likely to be magnified the most there.

Any faulty signal earth could be responsible.

Subject: Tech: Stereo hum
From: kendall
Date: 23 Feb 06 - 07:49 AM

I have a reasonably good sound system the works well on all but one mode. When I turn the phono on, I get a low hum. Even if the turn table is not on, it still hums. Any ideas? (Don't nobody suggest it hums because it doesn't know the lyrics)