Ground loop hum

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There are several threads discussing hum problems. But, I am still confounded (pl bear with me).

The Zen4 is finally up and running:

When switched on, but no input signal connection - silent.

When connected to portable CD player (running from a wal-wart transformer) headphone out - silent, great sound!

When connected to pre-amp - hum (both channels), it is not just 60Hz, modulates at a higher freq (sorry, no scope available).

The preamp, and CD player both have 2-pin plugs - cheater plug is useless. So, the problem has to be with new Zen.

The other power amp (Adcom) also has 2-pin plug and when connected to pre-amp is silent.

I tried connecting all components on a common extension chord - still humming.

I have both monos in one chassis. I have followed the wiring scheme as shown in the Zen4 article: the power supply grounds are connected to AC pins of common bridge (used for grounding). The + & - of common bridge are connected together and then to the ground pin on power connector (14ga solid copper). The ground pin of power connector is connected to (both) heatsinks (14ga solid copper). The PCBs are connected to heatsinks via 22 ohm 3 W resistors.
 
It's definitely a ground loop, and not a problem with the ground wiring within the amp itself, since the hum only appears when connected to the preamp.

Have you tried running the amp without the ground connected to the outlet?

If the hum goes away, then it is a problem with your house wiring. The ground is bonded to the neutral bus in your breaker panel, so if the ground wiring has a problem, and a potential develops between ground and neutral at your outlet, it can cause the hum. This would explain why you still had the hum when you used a common extention cord for all components.
 
Sparhawk said:

Have you tried running the amp without the ground connected to the outlet?

That is the next thing I was going to try today evening (got to buy a cheater plug).

Sparhawk said:

If the hum goes away, then it is a problem with your house wiring.

That would be bad - live in an appt. Time for moving to another appt? Is there any way I can prove it to appt people that ground is bad (other than making them listen to the hum - that would not be very convincing I guess).
 
jag said:

That would be bad - live in an appt. Time for moving to another appt? Is there any way I can prove it to appt people that ground is bad (other than making them listen to the hum - that would not be very convincing I guess).

You could try measuring AC voltage between the ground and neutral pins of the outlet. If it isn't close to 0V, the wiring is bad. :eek:
 
Safety First

All the usual disclaimers about how your first electrical shock can easily be your last apply, especially when contemplating defeating a safety ground connection.

Make sure that your outlet is wired properly (in the US black is usually used for hot, white for neutral, green for ground). They are sometimes reversed. I'm not sure which of the "skinny" or "fat" slots of a US outlet is supposed to be neutral. I use a circuit tester that lights up one way if it meets code, and another way if it is reversed.

If your preamp and amp are plugged into different circuits (two different outlets) you can also try to measure potential between the cases of the two devices.

Erik
 
Re: Safety First

eLarson said:
All the usual disclaimers about how your first electrical shock can easily be your last apply, especially when contemplating defeating a safety ground connection.
Erik

Definitely not going to run the amp without ground on a permanent basis with the baby running around.

eLarson said:

Make sure that your outlet is wired properly (in the US black is usually used for hot, white for neutral, green for ground). They are sometimes reversed. I'm not sure which of the "skinny" or "fat" slots of a US outlet is supposed to be neutral. I use a circuit tester that lights up one way if it meets code, and another way if it is reversed.
Erik

the small slot is black - hot, the large is white - neutral.

eLarson said:

If your preamp and amp are plugged into different circuits (two different outlets) you can also try to measure potential between the cases of the two devices.

Erik

already tried running all components from the same extension cord, still humming.
 
jag said:
Will something like this tell me about that? Thanks for all the help

That's definitely a good tool to have. But it will only tell you about major faults or miswiring. If the ground connection is correct, but not very good (ie. high resistance due to poor connections, etc) this tester may not indicate a fault. A multimeter would give you more information.
 
wuffwaff said:
do you have a tuner connected to your preamp? If this is the case try disconnecting the antenna.

william

That's a good point... I had a strange ground loop problem once that was resolved by disconnecting the cable TV from my tuner. The cable is supposed to be connected to ground somewhere, usually at the main breaker panel. But if it isn't, or if the connection isn't great, or the resistance of the cable is high, it makes for a very nice ground loop. :(
 
jag said:


No, no tuner, one input only - CD player (well actually a DVD player - Sony NS500V)

I take that back, actually I might have TV outputs connected to the pre-amp. And, TV is connected to cable. And, I know that the cable wire is really crappy. Will try disconnecting the TV connection and see where it takes me.

Thanks for all the input!
 
jag said:


I take that back, actually I might have TV outputs connected to the pre-amp. And, TV is connected to cable. And, I know that the cable wire is really crappy. Will try disconnecting the TV connection and see where it takes me.

Thanks for all the input!

That's what happened to me, actually... I had the cable connected to both the FM tuner on my receiver, and to the TV. The TV audio was connected to the receiver. I tried removing the cable from the receiver, and the ground loop was still present. Eventually I realized that it was via the TV audio. Ground loops can be incredibly devious. :scratch2:
 
so all you have to do now is to buy an ground loop filter wich connects between cable wall socket and cable to tv/tuner. (don´t know the english name but it decouples the earth with small capacitors). You can also build one yourself (there´s a thread on it somewere........)

william
 
Sparhawk said:


That's what happened to me, actually... I had the cable connected to both the FM tuner on my receiver, and to the TV. The TV audio was connected to the receiver. I tried removing the cable from the receiver, and the ground loop was still present. Eventually I realized that it was via the TV audio. Ground loops can be incredibly devious. :scratch2:

They sure are!

(BTW: the link from Radio Shack looks like the tester I bought at the hardware store. :) )

When I had my TV connected to the stereo I put a couple of back to back 300 to 75 ohm transformers into the cable TV line to ensure that the DC path is broken. I had to add a signal booster to the works, too.

(Sadly I did that on the cheap and it failed, leaving me with a snowy picture. I ended up just unplugging it all. I guess I'm not really cut out for home theater and the like. *heh*)
There was a fancy version of the same idea distributed by Madrigal called, if memory serves, "MAGIC".

Erik
 
No Hum!

Sparhawk said:

Ground loops can be incredibly devious. :scratch2:

You bet!

Well, the neutral to earth measured 0V. Also, TV outputs were not connected to pre-amp - but - cable connected to VCR, VCR connected to TV, DVD out connected to TV, and DVD out connected to pre-amp. There you go!

Thanks a lot to everyone for helping me out on this. Pictures of the new-born Zen4 tomorrow.
 
Homebrew CATV ground path isolator

Since I rated somewhere between a carrot
and a rock on the alertness scale yesterday
I didn't really explain what I had done very well.
It might be obvious, but in case its not, here's
how to build a quick ground-path isolator for
your cable TV line.

One xformer had flying leads on the 300-ohm
side, the other screw terminals. Also, one of
them had a female 75-ohm connector, while
the other had a male connector.

I connected the transformers together at the
300-ohm sides, connected the male 75-ohm
connector to the wall and the cable into the
female 75-ohm connector.

And finally my hum was gone. (Apparently
that was the last ground loop in that
particular setup.)

There will be loss due to each transformer,
of course, which will result in a noiser
picture. If you add an amplifier to boost
the signal, add it before the transformers to
maintain the best possible overall noise
figure.

Regards,
Erik
 
Re: Homebrew CATV ground path isolator

eLarson said:

I didn't really explain what I had done very well.
It might be obvious,

Oh, it was pretty clear - thank you. This Goldbergian contraption does take care of the hum.

eLarson said:

There will be loss due to each transformer,
of course, which will result in a noiser
picture. If you add an amplifier to boost
the signal, add it before the transformers to
maintain the best possible overall noise
figure.

The picture quality with cable TV is already crappy, and I don't think you can degrade it further. Some channels do seem to have a little bit more noise, but others are infact a lot more clear now. And, I did not use any signal amplifier either :D
 

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