Dish receiver causes speaker hum with three prong plug? - Page 1
Forum section: electronics / projects

author: p5200
author_rank: Contributor
timestamp: March 28, 2021, 04:28:00 pm
content: My Parasound a23 2 channel stereo power amp comes with a three prong plug. when using that type plug, I get speaker hum with Dish receiver hooked up feeding audio to preamp but not when it's not hooked up it, also has a three prong plug. I've been using two prong with power amp to defeat the speaker hum. I don't like using the two prong and loosing the grounding prong. I've been told on another forum that it was a common problem with Dish receiver use through stereo. Also, they mentioned the use of a ground loop isolator would solve the hum problem so I could use the factory 3 pronged plug that came with the power amp. Anyone familiar with the ground loop isolator they speak of? Through unhooking things, I for sure isolated the problem to be because of the Dish receiver which, was stated to be a common problem. I'd sure appreciate all input and, maybe some links to the type ground loop isolator others were referring to. Thank You!

author: p5200
author_rank: Contributor
timestamp: March 28, 2021, 05:17:29 pm
content: Could this maybe, be what I need?https://www.amazon.com/coax-ground-loop-isolator/s?k=coax+ground+loop+isolator

author: ejeffrey
author_rank: Super Contributor
timestamp: March 28, 2021, 05:23:55 pm
content: Does the dish receiver support TOSLINK optical output? If so use that.

author: richnormand
author_rank: Unknown
timestamp: March 28, 2021, 05:34:23 pm
content: You say the Dish is a three prong plug too? If so the hot/neutral could be in the wrong orientation. An AC isolation transformer might be needed. Or is it powered from a wall-wart type supply?On some of my older audio equipment I would put an AC DMM between the chassis and a known ground point and orient all the plugs to make sure the internal line cap was on the neutral side.That usually cured the hum that happens when the audio cables ground/shield side would create a ground loop between two units.On the other hand if both have a three prong plug make sure both are on the same socket/circuit not to create a ground loop all the way to the junction box.If you have a DMM with AC scale measure the AC between the two units without any other connections between them.In one case my issue was with the cable box and it turned out to be the cable TV coax coming to the house that was not properly bonded to the house ground and was doing so via whatever equipment was connected to the cable box (HDMI to TV and audio to amps) via a three prong plug.

author: p5200
author_rank: Contributor
timestamp: March 28, 2021, 05:36:47 pm
content: Thanks I'll do some checking!

author: p5200
author_rank: Contributor
timestamp: March 28, 2021, 05:41:53 pm
content: Dish is also three prong

author: ejeffrey
author_rank: Super Contributor
timestamp: March 28, 2021, 06:40:03 pm
content: This is a pretty standard ground loop issue. It's likely not particularly "dish specific" except that dish receivers are grounded while lots of residential AV equipment uses 2 pin power connectors. You are correct that ideally you don't want to do that if the equipment wasn't designed that way. I wouldn't mess around with isolation transformers. That might solve the "problem" but won't be any safer than disconnecting the ground pin, since the amplifier already has isolation built in. Likewise, don't mess with the EMI capacitors in the amplifier.Unless a really bad electrician has worked on your house wiring the live and neutral will not be swapped. It can happen but is pretty rare in the US.Commercial equipment is almost always grounded, and this is one of the reasons why the usually have balanced inputs. Balanced inputs pretty much solve the ground loop issue, and I see your amplifier has balanced inputs, but presumably the dish receiver doesn't have balanced outputs.Basically this is a problem of using a not-great equipment pairing. You would be much better off either using a source with balanced outputs or an amplifier with a 2 pin plug or that supports digital input such as SPDIF/TOSLINK or HDMI.It may be possible to use the amplifiers balanced inputs. Its possible to get a cable that will connect the (-) input of the balanced signal to the RCA outer conductor to create a pseudo-balanced signal. This won't be as good as the real thing as the impedance will not be balanced as well as a true balanced output but it might be good enough. Here is an example (I have no idea if this is any good)https://www.amazon.com/Monoprice-XLR-Male-RCA-Cable/dp/B001VLW398The other option would be to create true balanced signals with audio transformer.

author: themadhippy
author_rank: Super Contributor
timestamp: March 28, 2021, 07:02:42 pm
content: QuoteThere just a 1 to 1 isolation transformer used on the audio,not mains lines,commonly found in the car audio world and AV industry,shouldn't cost you more than a couple ofquiddollars

author: BrokenYugo
author_rank: Super Contributor
timestamp: March 29, 2021, 06:18:19 pm
content: Quote from: ejeffrey on March 28, 2021, 06:40:03 pmDepends a lot on the house, I've found reversed polarity to be quite common in older houses and rentals. Same goes for floating grounds and bootleg grounds (hopefully neutral strapped to the ground terminal).

author: richnormand
author_rank: Unknown
timestamp: March 30, 2021, 05:35:30 pm
content: That is why these small $12 LED outlet line testers found in most hardware stores are so useful in these situations.When I bought a house I found one outlet with the neutral reversed.

author: BrokenYugo
author_rank: Super Contributor
timestamp: March 30, 2021, 08:27:47 pm
content: Be careful with the simple 3 led/neon testers, they won't find a bootleg ground or identify a reversed polarity if the ground is floating or worse yet strapped to live. BAD IDEA AHEAD, DO NOT TRY AT HOME: I keep mine plugged into a cheater plug so I can float the tester and touch the ground tab to provide my own ground reference,do this at your own risk.I'm of the opinion a cheap non contact detector stick does a better job if you know how to use it. Or a DMM, which will show the zero potential between ground and neutral on a bootleg ground.