Author Topic: Shielded against 60Hz speaker cable  (Read 1005 times)

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Offline Hextejas

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Shielded against 60Hz speaker cable
« on: March 15, 2019, 11:13:12 pm »
I am having a heck of a time trying to eliminate a 60Hz hum from one of my speakers. So, I was wondering if someone makes a 60Hz shielded cable that I could use.
Or could I possibly wire some kind of a filter at the end of the speaker cable that would filter out the 60Hz hum.

thanks
 

Online Cliff Matthews

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Re: Shielded against 60Hz speaker cable
« Reply #1 on: March 15, 2019, 11:43:26 pm »
Look for hum in the gain stages of audio amp and not the speaker cables. Amp outputs are low impedance 4-16 ohm, so it's an unlikely source. Perhaps you have an amp with separate bridges and caps for each channel? (one leaky filter cap maybe?)

It's also possible the biasing on that channel is very close to frying an output transistor, so with no signal input you should have almost no AC or DC offset voltage on that channels output terminals. You'll need to provide a bit more info..  :-//
 

Offline bson

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Re: Shielded against 60Hz speaker cable
« Reply #2 on: March 15, 2019, 11:44:14 pm »
I'd go look for a ground loop, bad filter cap in the amplifier/source, or other causes.
 

Online soldar

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Re: Shielded against 60Hz speaker cable
« Reply #3 on: March 15, 2019, 11:50:06 pm »
I am having a heck of a time trying to eliminate a 60Hz hum from one of my speakers.

Have you tried switching the speakers one for the other and see if the hum stays with the speaker or with the amp channel?
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Online DimitriP

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Re: Shielded against 60Hz speaker cable
« Reply #4 on: March 16, 2019, 12:25:14 am »
(tapping impatiently)
   If three 100  Ohm resistors are connected in parallel, and in series with a 200 Ohm resistor, how many resistors do you have? 
 

Offline Hextejas

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Re: Shielded against 60Hz speaker cable
« Reply #5 on: March 16, 2019, 02:34:49 am »
Yes I have switched them and the hum stays with the channel. Good idea though. Thanks.
 

Online Cliff Matthews

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Re: Shielded against 60Hz speaker cable
« Reply #6 on: March 16, 2019, 03:08:36 am »
More setup info req'd... are these powered or bi-amped speakers? Make model of amp etc.. move the problem channels cable away from in-floor / in-wall mains wiring (on the off-chance amp has some weird bootstrap cap feeding back something from the cable..)
 

Online soldar

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Re: Shielded against 60Hz speaker cable
« Reply #7 on: March 16, 2019, 10:59:37 am »
Yes I have switched them and the hum stays with the channel. Good idea though. Thanks.

So the problem is with that amplifier channel and not with the speaker or its cable (as was 99.9% likely). Why are you looking for shielded speaker cable? Why are you not troubleshooting that amplifier channel?

Are both channels powered from a common supply? Is the supply stable? Have you checked all the electrolytic caps on that channel?
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Offline Hextejas

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Re: Shielded against 60Hz speaker cable
« Reply #8 on: March 16, 2019, 12:30:46 pm »
I think that it has to do with the position of the speaker cable. Because when i elevate the offending cables the hum goes away. I have tried to move them as far away from power cords and that helps. There are 2 speaker cables to the right speaker due to the use of a sub woofer. And the sub woofer is about 20’  feet from the amp and the speaker cables have to avoid 3 power cords. If i hold the cables about 4 feet above the floor the hum disappears.
The idea of rebuilding the amp does not appeal since i have already done it 4 times due to another mistake.
There is a separate power supply feeding both amps,
 

Online Cliff Matthews

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Re: Shielded against 60Hz speaker cable
« Reply #9 on: March 16, 2019, 01:00:42 pm »
Looks like you're getting closer to solve this.. So we see the offending speaker cable runs from an amp with its own power supply is running parallel with the other speaker cables. It may be that amps power supply is floating and the other channels amp and the sub-w's amp are at the same ground potential. Time to breakout a DMM and measure grounding disparity.
 

Offline Hextejas

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Re: Shielded against 60Hz speaker cable
« Reply #10 on: March 16, 2019, 02:24:04 pm »
Looks like you're getting closer to solve this.. So we see the offending speaker cable runs from an amp with its own power supply is running parallel with the other speaker cables. It may be that amps power supply is floating and the other channels amp and the sub-w's amp are at the same ground potential. Time to breakout a DMM and measure grounding disparity.

Cliff, thank you. I would love to do this if I knew how. I am new to this electronic "stuff" and it's mostly a mystery. Can you explain in simple terms how to do this ? I will be forever in your debt.
 

Online Cliff Matthews

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Re: Shielded against 60Hz speaker cable
« Reply #11 on: March 16, 2019, 03:52:57 pm »
You must have a volt-meter, since you've already rebuilt the amp 4 times?
1) Power-on both amps (minimum volume and nothing connected to inputs) measure and report DC and AC differences between both amps output terminals.
2) Report any DC voltage present (however small) at the output terminals on each amp.
3) Power-off both amps, disconnect from mains and wait a few minutes for amp PSU caps to discharge. Report resistance between positive and negative output terminals to chassis ground on each amp.
4) Still disconnected from mains, report resistance from the chassis of each amp to its wall plug connector (to see if open).

There may be other checks others may want to add, but these are just a few.
 

Offline coromonadalix

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Re: Shielded against 60Hz speaker cable
« Reply #12 on: March 16, 2019, 06:13:47 pm »
you can short your amp input at 0 ohms  and see and follow your hum in the circuits ...    the short will garanty  nothing enter or no antenna effects / noise picking, or defective signal input cables.

Even saw long time ago, bad grounding for the frame screws to a ground tab/log  on pcb's, even checked main ac sockets for proper wiring ...


What is the amp model ??
« Last Edit: March 16, 2019, 06:18:30 pm by coromonadalix »
 

Online DimitriP

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Re: Shielded against 60Hz speaker cable
« Reply #13 on: March 16, 2019, 06:41:15 pm »
Quote
I think that it has to do with the position of the speaker cable.

Did you end up removing temporarily or routing the speaker wires away from the UPS?
   If three 100  Ohm resistors are connected in parallel, and in series with a 200 Ohm resistor, how many resistors do you have? 
 

Offline Hextejas

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Re: Shielded against 60Hz speaker cable
« Reply #14 on: March 17, 2019, 03:26:04 pm »
Quote
I think that it has to do with the position of the speaker cable.

Did you end up removing temporarily or routing the speaker wires away from the UPS?

I did this partially which I think helped the left speaker.  The amps and power supply are on a mains circuit by themselves. The left speaker is free of hum. But there is a UPS in the path of the right speaker so I will try removing it entirely.

Separate question. The UPS has a heavy battery in it. Can the battery contribute to the hum problem ?

The sub woofer I think, is part of the problem. It is located near the right speaker with its own power cord plugged into a separate wall receptacle. For a short length, the right speaker cable parallels the sub woofer power cord.
I am gonna take the sub woofer out of the chain and see what happens. I will post my findings later.

I really appreciate all this excellent help.
 

Offline Hextejas

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Re: Shielded against 60Hz speaker cable
« Reply #15 on: March 17, 2019, 08:34:21 pm »
You must have a volt-meter, since you've already rebuilt the amp 4 times?
1) Power-on both amps (minimum volume and nothing connected to inputs) measure and report DC and AC differences between both amps output terminals.
Please be aware that this is new to me so I might be doing things the wrong way. For task 1 I measured the voltages with the probes on the +(Red)  and -(Black) of the amp outputs which are what are connected to the speakers.
So:
Left DC =0
Left AC=0
Right DC=.003
Right AC=0

2) Report any DC voltage present (however small) at the output terminals on each amp.
I am assuming that you want the voltages measured with a reference to chassis ground.
So:
All are 000 with the exception of the Right DC=.005

3) Power-off both amps, disconnect from mains and wait a few minutes for amp PSU caps to discharge. Report resistance between positive and negative output terminals to chassis ground on each amp.
All readings are ohms
Left --- = 0k
Left +++ = 41.3k
Right --- = 0k
Right +++ = 41.7k

4) Still disconnected from mains, report resistance from the chassis of each amp to its wall plug connector (to see if open).
No connections are open and they report a small ohm reading.

These readings might give you a clue but they are meaningless to me. However I wonder where the small DC voltage on the right channel is coming from.

I removed the sub woofer from the chain and it made no difference. I routed the cable many different ways and was able to get the hum to a minimum level though I hear a strange tic, tic, tic sound like the sound at the end of a record being played. There is also a faint signal from a radio station. Weird !
The problem I have with the present routing of the cable has to do with an unhappy spouse. Admittedly the routing is ugly.
 

Online Cliff Matthews

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Re: Shielded against 60Hz speaker cable
« Reply #16 on: March 17, 2019, 10:40:51 pm »
All looks OK, but the presence of a UPS I did not know about.. some UPS's run a stepped square-wave through the output transformer even when idling, so this could be the source. Why it's even never near an audio system I cannot guess.
« Last Edit: March 17, 2019, 11:29:54 pm by Cliff Matthews »
 

Offline Hextejas

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Re: Shielded against 60Hz speaker cable
« Reply #17 on: March 20, 2019, 03:34:06 am »
Well, I saw that one of the input RCA plugs was slightly loose so I decided to fix it. Then I discovered that the grounding wire was not making contact with the chassis,  a poor wiring job. When I corrected that, the 60Hz hum pretty much disappeared..
So, I owe a hearty thanks to all that helped me and sorry for the shoddy job.
 

Offline NiHaoMike

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Re: Shielded against 60Hz speaker cable
« Reply #18 on: March 20, 2019, 04:32:42 am »
Separate question. The UPS has a heavy battery in it. Can the battery contribute to the hum problem ?
Not the battery itself but I used to have a Belkin UPS that used a pulse charging circuit that really likes to induce noise into nearby analog audio amplifiers. It worked by shorting the low voltage side of the transformer for a brief moment and then letting the leakage inductance work as a boost converter. It doesn't help that it was a $10 or so special with a plastic case...
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Online DimitriP

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Re: Shielded against 60Hz speaker cable
« Reply #19 on: March 20, 2019, 07:16:51 pm »
Quote
Then I discovered that the grounding wire was not making contact with the chassis,

It could've been a lot worse: Somone could have posted a part number for shielded speaker cables.
Be glad no one did :)
   If three 100  Ohm resistors are connected in parallel, and in series with a 200 Ohm resistor, how many resistors do you have? 
 

Offline Hextejas

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Re: Shielded against 60Hz speaker cable
« Reply #20 on: March 21, 2019, 11:06:04 am »
Quote
Then I discovered that the grounding wire was not making contact with the chassis,

It could've been a lot worse: Somone could have posted a part number for shielded speaker cables.
Be glad no one did :)
e
Hahahaha  well I deserve to have my wrist slapped.
 


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