Topic: Hum Help!

[SonicSound]

PLEASE HELP!

I thought my days of the good old 60Hz hum were over.  I have been in a new home for the last year and had not experienced any ground loop challenges. And then I decided to put the A/V equipment in the basement and feeding a first floor listing/audio room (controlled by a universal remote).  The only thing I changed was running out of the A/V receiver (Yamaha 2600) through the pre-out through my audio only stereo pre-amp (Spectral DMC-30SL) and using two outlets to power the system.  This was all done so that I (my wife) did not have to change speaker wires when switching between TV/Video and high end audio listening.  At first I thought it was because I was using two different outlets.  But after I rewired using the same outlet it was still there. 

I believe that I have isolated it to the Comcast cable box. This is a HD unit manufactured by Motorola.  Strangely enough, when it is all hooked (excluding the cable box being plugged in to a power outlet and the actual cable connected) the hum still exists.  I do not think it’s the cable feed, it’s something with the cable box.

Your help will be greatly appreciated.

[Church-Audio]

PLEASE HELP!

I thought my days of the good old 60Hz hum were over.  I have been in a new home for the last year and had not experienced any ground loop challenges. And then I decided to put the A/V equipment in the basement and feeding a first floor listing/audio room (controlled by a universal remote).  The only thing I changed was running out of the A/V receiver (Yamaha 2600) through the pre-out through my audio only stereo pre-amp (Spectral DMC-30SL) and using two outlets to power the system.  This was all done so that I (my wife) did not have to change speaker wires when switching between TV/Video and high end audio listening.  At first I thought it was because I was using two different outlets.  But after I rewired using the same outlet it was still there. 

I believe that I have isolated it to the Comcast cable box. This is a HD unit manufactured by Motorola.  Strangely enough, when it is all hooked (excluding the cable box being plugged in to a power outlet and the actual cable connected) the hum still exists.  I do not think it’s the cable feed, it’s something with the cable box.

Your help will be greatly appreciated.

I don't get the last part its confusing.. You say you think its the cable box. But when the cable box is not connected to the cable or to an ac outlet you still have hum?? I think its always a mistake to power a stereo from two different plugs in two different parts of a house. The main problem with that is you don't know what is also sharing that outlet with your stereo... You could also have an outlet that's not wired correctly Neutral to hot reverse. This is a common issue. I would go around the house and check your outlets with a simple outlet tester. I would try to plug everything back in to one power source (just to test it) if you get hum eliminate things one by one until the hum stops. Don't pull more then one thing out of the chain at a time. If its something like a satellite receiver you can by a hum eliminator *basically a transformer 1:1 ratio line in to line out. This transformer will isolate the output of your receiver from your stereo but before we go all nuts buying stuff try the outlet tester and try putting both devices on the same circuit. The problem with splitting circuits is that you don't know what phase of the house power each device is on this can create all kinds of issues. With home audio its always a challenge because everything is unbalanced for the most part unless its high end gear and you cant go lifting pin 1 ground because you are most likely running everything unbalanced.. Let me know how you make out.

[IowaClint]

Yo,  I have had the same problem.  It was the cable, try a different cable.  I was using a 75ohm cable but the shielding wasn't good enough and bumped it to I think 90ish.  It was something we had lying around in engineering stock.  Worked like a charm. 
~Clint

[SonicSound]

Sorry if I am not lucid … it is Friday and I am unwinding.

The unit (cable box) is hooked up (l/r audio and component video) to the A/V receiver, however the unit is not plugged in and the cable feed is not connected.  Under these conditions there still is a hum.  As I mentioned, I did try to power every thing form the same outlet and the hum was still there.  I will try tomorrow to see if the outlet is wired correctly, though wouldn’t this effect phasing not ground loop?

Thanks for the feed back +T

I don't get the last part its confusing.. You say you think its the cable box. But when the cable box is not connected to the cable or to an ac outlet you still have hum?? I think its always a mistake to power a stereo from two different plugs in two different parts of a house. The main problem with that is you don't know what is also sharing that outlet with your stereo... You could also have an outlet that's not wired correctly Neutral to hot reverse. This is a common issue. I would go around the house and check your outlets with a simple outlet tester. I would try to plug everything back in to one power source (just to test it) if you get hum eliminate things one by one until the hum stops. Don't pull more then one thing out of the chain at a time. If its something like a satellite receiver you can by a hum eliminator *basically a transformer 1:1 ratio line in to line out. This transformer will isolate the output of your receiver from your stereo but before we go all nuts buying stuff try the outlet tester and try putting both devices on the same circuit. The problem with splitting circuits is that you don't know what phase of the house power each device is on this can create all kinds of issues. With home audio its always a challenge because everything is unbalanced for the most part unless its high end gear and you cant go lifting pin 1 ground because you are most likely running everything unbalanced.. Let me know how you make out.

[SonicSound]

Very interesting, however as I pointed out the hum even exists when the cable is not hooked up to the unit.   I still might try this however.  +THanks

Yo,  I have had the same problem.  It was the cable, try a different cable.  I was using a 75ohm cable but the shielding wasn't good enough and bumped it to I think 90ish.  It was something we had lying around in engineering stock.  Worked like a charm. 
~Clint

[Church-Audio]

Very interesting, however as I pointed out the hum even exists when the cable is not hooked up to the unit.   I still might try this however.  +THanks

Yo,  I have had the same problem.  It was the cable, try a different cable.  I was using a 75ohm cable but the shielding wasn't good enough and bumped it to I think 90ish.  It was something we had lying around in engineering stock.  Worked like a charm. 
~Clint

Remember dont get ahead of your self buying new cable until you have found out what peace of gear is going making your noise happen. Try disconnecting inputs on your receiver one at a time until the hum is gone..
As for what you said about the Hot and Neutral it can cause these types of problems but the first problem it can cause is death... So I always like to check all the outlets in a house when I first buy it or move in because I know who it is that wires the outlets in most houses its not the electrician its the apprentice. I think everyone that owns a house or lives in one should own a basic outlet tester and know how to use it. For $7.96 this could save a life.. http://www.globaltestsupply.com/test_equipment/AEMC_OT-1_Outlet_Tester_.cfm

[SonicSound]

I dug out the old outlet tester and much to my sunrise it seems that the entire house is wired in reverse (hot/neutral reversed).  This makes me think that the main feed is not wired correctly.

I am not sure if I am up for switching all the wiring in the house.  Should I just hire an electrician to fix the feed?   

I did correct the outlets which are associated with the  a/v devices and the hum is still there

[Church-Audio]

I dug out the old outlet tester and much to my sunrise it seems that the entire house is wired in reverse (hot/neutral reversed).  This makes me think that the main feed is not wired correctly.

I am not sure if I am up for switching all the wiring in the house.  Should I just hire an electrician to fix the feed?   

I did correct the outlets which are associated with the  a/v devices and the hum is still there

Ummm I dont think your house is wired in reverse :_) That would be, I am not going to use the word impossible but very VERY unlikely the electrician would have to be a huge moron. And besides its impossible for main feed to be backwards why??? You have two hots and only One Neutral. and there is no way it could be that way. The second reason is it would trip the main breaker the minute it was turned on. So if every outlet is showing reversed. I would buy a new outlet tester and try again to make sure. One simple way to determine Neutral is a volt/ohm meter between ground and Neutral there should be 0volts... The Neutral in a standard outlet is always the larger of the two slots... The small slot is HOT. between the small slot and ground there should be 110volts. MAKE sure you set your meter to AC and at its highest voltage range.... If you get a voltage between the LARGE SLOT and GROUND your outlet is ass backwards. And you need to rewire that outlet. Hiring an electrician if your not comfortable with this would be a good thing.. But get a different outlet tester first. Unless your 100% sure yours works. Because there is no way your service entrance is backwards Its not possible. Good luck let me know what happens I doubt now that this is the cause of your hum but This condition if it really does exist is extremely dangerous and can KILL YOU OR SOMEONE if its not fixed.......

[SonicSound]

Church,
Thanks for the explanation.  I am going to HomeD in a few to pick-up a new tester. 

What is the hazard with having lighting wired in reverse and how do I test it? 

I checked some outlets in the kitchen (a few outlet/switch receptacles) and tester indicated reversed wiring. 

[Church-Audio]

Church,
Thanks for the explanation.  I am going to HomeD in a few to pick-up a new tester. 

What is the hazard with having lighting wired in reverse and how do I test it? 

I checked some outlets in the kitchen (a few outlet/switch receptacles) and tester indicated reversed wiring. 

Here is the issue.. I will use a guitar amp as an example..

Some guitar amps mostly tube ones the Neutral is connected to ground.. So if your guitar is grounded to your amp. Then your guitar strings are grounded to you.. When you reverse the AC outlet now all of a sudden if your playing guitar your stings are HOT. If you touch ground anything grounded YOUR DEAD. Now we dont use 2 prong plugs for a lot of things anymore but there are still used for some things. So the proper termination of an AC outlet is critical to its safe operation. Also appliance companies tend to use more insulation on the HOT side of a two prong appliance then they do on the Neutral. You brought up lighting.... Lets say you were on an aluminum latter on a concrete floor and you unscrewed the light bulb and touched the threaded part. If the socket was wired correctly, your in no danger what so ever. If its reversed the threads are HOT your at ground potential because of the concrete floor and your sitting on a huge conductor the aluminum latter = your dead. Now you might not die you might just get the living shit shocked out of you. But I would rather just make sure everything is wired correctly. If you find everything is backwards you need to stop.. Pickup the phone and call an electrician in to check your house out.

[pfife]

if you still have the problem narrowed down to the cable box you could try exchanging it for a different one.  I swapped a dvr box with Comcast because it was actin a fool, no questions asked.

[SonicSound]

Church,
I purchased a new outlet tester and it indicated that outlets are wired correctly.
Not sure which one to believe 
Hope it’s the new tester. Will have to call an electrician to verify proper wiring and have him look into the ground loop issue.

[SonicSound]

I have eliminated the hum!

But not sure if this is a good setup

Overall Setup:
I am using two power outlets.  One is located on the first floor of my house (in the family/listing room) and the other is directly below in the basement.

First Floor Connections:
Pre-amp, power amps, DAC, and CD transport all connected to a power strip that is connected to the outlet using a cheater plug (with the ground lifted).

Basement Connections:
A/V receiver, cable box, TV (TV is located on first floor), and dvd player all connected to a power conditioner and connected to power outlet (without a cheater).

What am I risking by using the cheater plug?

[Church-Audio]

I have eliminated the hum!

But not sure if this is a good setup

Overall Setup:
I am using two power outlets.  One is located on the first floor of my house (in the family/listing room) and the other is directly below in the basement.

First Floor Connections:
Pre-amp, power amps, DAC, and CD transport all connected to a power strip that is connected to the outlet using a cheater plug (with the ground lifted).

Basement Connections:
A/V receiver, cable box, TV (TV is located on first floor), and dvd player all connected to a power conditioner and connected to power outlet (without a cheater).

What am I risking by using the cheater plug?

Well you have eliminated the ground loop by removing your safety ground.. This is not the way to solve this issue. I would not recommend it. It sounds like something is grounded somewhere else. I think you should do the process of elimination we talked about by putting your ground back and unplugging inputs on your receiver until the hum goes away. Its never a good idea to bypass a electrical ground on a device.

[SonicSound]

It’s not the cable box.  I went to Comcast and exchanged mine for a different one (this one has HDMI sweet).  I am pretty sure (if not positive) it’s the cable.  I carefully rechecked connections.  With every thing connected excluding the cable to the cable box, the hum is eliminated.  I tried a fix which uses two 75ohm to 300hom antenna transformers, following the instructions given at this website: http://www.dplay.com/tutorial/cablehum.html
I ran down to my local Radio Shack, to pick up the parts as specified with confidence.  Got home and installed the “trick” and there it was although much less pronounced.  Is this because there is not enough shielding?

I am getting very agitated after a full day of hunting for hum!  I really want to just use the cheater and be done with it.

I have to believe this can be solved.  Can I ground the cable so that it is on the same grid as the house or better yet the outlet circuit?  I am obviously not an electrical engineer or electrician, please keep the options coming.