some AC outlet causing hum on my amplifier!

[gychang]

I have several AC outlets in my music room. I also have 2 amps-speaker combos in the same room (only play one set at a time) and found out now that only one AC outlet is hum free. The others result in AC hum irregardless of combination of amp-speakers (not coming from amps). I am guessing it may be the home wiring (only 11 year old home).

1. Is there a device I can plug in the AC outlet that will eliminate speaker hum (low volume can't hear, mid volume setting start to hear, and maximum setting quite loud). I use t-amp clone and various diy fullrange speakers.

2. Is there a home structure problem?

Is this something I can trouble shoot with my DIMM meter?

thanks in advance

[LCHIEN]

there can be many sources of AC hum in a an audio system.

The very first thing I would do is suspect the grounding system is either not connected or connected backwards. To check this there are 2 ways you can do this.
1. Go to the hardware store and buy a AC receptacle checker... like these
http://www.lowes.com/pd_292767-12704...ter&facetInfo=
http://www.amazon.com/50542-Receptac.../dp/B002LZTKIA
they're under $10 and tell you at a glance if the Ground is missing or you have your hot and neutral wires crossed on that circuit, either problem is a good candidate for hum and is also dangerous. Costs less than $10 and when you get one you should check every outlet in your house!!! You should have one of these!!!
2. Use your DMM, set it to 200ACV or Auto ACV range and make a table of three voltages: H-N, G-N, and H-G
To do this you need to know which blade slot is hot and which is neutral. I can't remember and always have to look it up (see below). And, be careful with live probes. (That's 2 reasons why method 1 is better for most people!).
should have: H-N approx 120V, H-G approx 120V, and G-N less than about 5V.
here from the living with my home website:



Anyway try this first and let me know the result for the good outlet and all of the bad ones. Since your problem is outlet dependent, I'm suspicious on this first. One branch may be wired wrong and your one good outlet is on another branch.

Also, with your DMM on ohms, check and make sure the ground on the good outlet is connected to the grounds on the other outlets.

[All Thumbs]

Do you have any dimmers (for lights) in the room? I've had dimmers do some pretty interesting things, even when they aren't controlling the outlet they are connected to.

[gychang]

there can be many sources of AC hum in a an audio system.

The very first thing I would do is suspect the grounding system is either not connected or connected backwards. To check this there are 2 ways you can do this.
1. Go to the hardware store and buy a AC receptacle checker... like these
http://www.lowes.com/pd_292767-12704...ter&facetInfo=
http://www.amazon.com/50542-Receptac.../dp/B002LZTKIA
they're under $10 and tell you at a glance if the Ground is missing or you have your hot and neutral wires crossed on that circuit, either problem is a good candidate for hum and is also dangerous. Costs less than $10 and when you get one you should check every outlet in your house!!! You should have one of these!!!
2. Use your DMM, set it to 200ACV or Auto ACV range and make a table of three voltages: H-N, G-N, and H-G
To do this you need to know which blade slot is hot and which is neutral. I can't remember and always have to look it up (see below). And, be careful with live probes. (That's 2 reasons why method 1 is better for most people!).
should have: H-N approx 120V, H-G approx 120V, and G-N less than about 5V.
here from the living with my home website:



Anyway try this first and let me know the result for the good outlet and all of the bad ones. Since your problem is outlet dependent, I'm suspicious on this first. One branch may be wired wrong and your one good outlet is on another branch.

Also, with your DMM on ohms, check and make sure the ground on the good outlet is connected to the grounds on the other outlets.

this is great, thanks

[gychang]

Do you have any dimmers (for lights) in the room? I've had dimmers do some pretty interesting things, even when they aren't controlling the outlet they are connected to.

yes I have one dimmer that is taped so I use it as on-off, thanks for the possible culprit.

[Daryl]

There are chokes and filters that are installed on the cord of the amps that will cut the hum back, go to Radio Shack and tell them your problem, they should be able to help you. What you are hearing is the 60 cycle hum from dimmers, flourescent lights, refrigerators, furnace transformers, etc. You might want to look into a dedicated line from your breaker box to your music room.

[Dal300]

Not sure if this is the problem or not, but when I use a couple of different cords that I have laying around, I get that hum. Sometimes it goes away when I turn the cords around, sometimes I need to use another cord.

My amp doesn't really seem to be the problem, I can use either my Fender Twin or my little Rogue 10. One is tube type, one is electronic. The problem seems to be in the guitars themselves. I have a 1960's Fender Mustang rebuilt in the 70's and a 1980's Oscar Schmidt, (Washburn) acoustic/electric. Both will have the problem, but turning the cord around or changing the cord seems to be a big help.

It also doesn't seem to matter what circuit I'm plugged in to. There seems to be no difference between any of the receptacles in the house or the ones down at the shop, which is even on a different transformer and pole.

[dbhost]

Assuming enough similarities between guitar, and bass guitar, I can speak from a somewhat limited experience...

I have played through an Ampeg SVT tube head to a solid state power amp, and several solid state all in one amps (Crate MBX10, and Crate BX100) with similar results.

No matter the amp, and in most locales I have played, I found that certain guitar cables always seem to cause a hum. Specifically the ones that have a simple rubber / silicone jacket, thin shielding, and what look to be chrome connectors. I have found that the thickly shielded tweed jacketed, gold tipped cables worked best for me. Both for transferred tone, and eliminating hum. The cables I use I can't seem to find on the site any more, but they were sold by Musicians Friend under their house name. They currently have a model with a 90 degree end that is otherwise identical. The Fender vintage voltage instrument cables work very well too...

FWIW, my instruments are an early Ibanez SR-500 (early 1990s I believe, I bought it WELL used in 2002), and a 2002 Ibanez SR480. The 480 is dead stock except it has been fitted with round wound GHS strings, the 500 has EBC pickups, aftermarket tuning machines, and is fitted with GHS bass boomers. (It's got a nasty, deep, very punk / metal growl to it...)

Now this isn't always the case, but this is a good area to eliminate hum. Failing this, and actually WITH this, if it's YOUR place, check your receptacle wiring, particularly the grounding... A bad ground can cause nasty hum...