[jmdesignz2]

Strange thing- (background info - I have 2 dedicated 20amp circuits)

I had an isolation transformer hooked to my amps using balanced cables - no hum
switched to unbalanced cables since new DAC was rca - got hum
took iso trans out of system, connect amps directly to dedicated 20amp - no hum
went back to balanced and direct to dedicated 20amp - no hum

It's rained very hard for the past day or two - got a new hum
noticed it on turning off the amps - they would make a kind of static laden squeal noise that diminished to 0 in about 2 seconds both channels
now, turning on the amps, there is a noticeable higher frequency hum in both channels

Any thoughts? Nothing has changed except it's rained hard all night and the day before
the hum is a bit higher in frequency than what I heard with the iso trans in the system with DAC > unbalanced >amps connection

[Wayner]

Could relate to your home's grounding rod for the electrical system.......

[jmdesignz2]

I do suspect that and hope someone has a more definitive answer / solution

[jmdesignz2]

Funny thing is that it has rained for longer and harder before this year and never had this unique hum noise

[Wayner]

I do suspect that and hope someone has a more definitive answer / solution

If you don't like my answer, then tuff hop.

[jmdesignz2]

If you don't like my answer, then tuff hop.

Apologies, did not mean to offend. Just looking for more info

[charmerci]

I assume you disconnected the DAC to make sure that or its cable wasn't the source. The rain could have just been co-incidental.

[Bob2]

I would look closer at wayner's suggestion.
Had a similar issue myself a few years ago... 

[decal]

Jeez Wayner, lighten up!!!!!!!!

[srb]

TUFF Hop is an Imperial/Double IPA brewed by Panimo Hiisi in Jyväskylä, Finland.

 

[DaveC113]

There's no doubt rain is reducing the ground rod/earth impedance but I can't see how that could cause noise to increase.

Switching from XLR to RCA makes your system more susceptible to issues including ground loop hum... generally not a problem in home systems but you may have an issue.

I'd try running your entire system on a single 20A line, or if that's not possible due to massive amps, try bonding the grounds of both lines together as close to your system as possible. Ideally, there would be a EMI/RFI filter, surge eliminator and power distribution box your entire system is plugged into, with two lines you need two of these boxes, and bonding these boxes together using large gauge wire may significantly reduce noise.

[*Scotty*]

You could try putting shorting plugs in the input jacks which will ground the inputs of the amplifier. When the inputs are grounded and the amplifier is turned on any hum or noise you hear is only being produced by the amplifier alone. If it makes the same noises when you shut it down and has a hum when turned on I suspect it might be one of your main storage caps in the power supply going bad. When one of your power supply rails has a different voltage than the other funny things can happen to the amplfier. This can happen if one of the main storage caps is failing. When you turn off the amplifier the storage caps keep suppling power to the circuitry in the amp until all of power stored in them is used up. If one of storage caps is failing it will have a lot less energy stored in it and will be exhausted first which can result in a voltage imbalance on the differential input. This can cause the funny noises you hear when the amp is powering down. The noises are probably the amp oscillating because of what is happening at the front end.
 Of course this is only a hypothesis and something else may actually be going on.
Good with your trouble shooting.
Scotty

[JRace]

I do suspect that and hope someone has a more definitive answer / solution

If you don't like my answer, then tuff hop.

Maybe your answer was neither definitive, nor provided a solution?

OP: Reminded me of this:

https://news.ycombinator.com/item?id=13347699

We had a similar thing happen with our cable... we'd get high upload latency and packet loss when it rained.
Turned out that the contractor who replaced the coax on our block didn't use the right grade of cable... the weight of the water plus wind would stretch the cable and open a crack in the housing.

Which also took me to here:
http://www.ibiblio.org/harris/500milemail.html

"We can't send email farther than 500 miles from here," he repeated.  "A
little bit more, actually.  Call it 520 miles.  But no farther."

I would be interested if you hear any hum using RCA muting plugs
http://darrenriley.com/wp-content/uploads/2014/02/1934.jpg

REal easy to make (just cut an old RCA cable, connect the +/- together,
Will not harm the amp, and will rule out the amp itself as the source of the noise.

[jmdesignz2]

Hi - just to make things clear

The hum is happening when I am using the Balanced DAC XLR > amps

Previously, I did have a hum caused by the ISO trans with the Unbalanced dac. I took the iso trans out = no hum

then I put in the XLR Dac = no hum

THEN recently it rained very hard and now have a Different higher frequency hum
Also when I turn the amps off - I get a strange squeal / buzz from the speakers that fades out as the amps discharge the capacitors.

I'm going to check the lines outside and check the grounding wires outside

[Big Red Machine]

Something quick you could check is run the system off a different breaker to eliminate anything inside with that circuit.

Sounds like the ground is not tight outside. Can you put another rod in and move the copper cable to it without splicing?

[jmdesignz2]

You could try putting shorting plugs in the input jacks which will ground the inputs of the amplifier. When the inputs are grounded and the amplifier is turned on any hum or noise you hear is only being produced by the amplifier alone. If it makes the same noises when you shut it down and has a hum when turned on I suspect it might be one of your main storage caps in the power supply going bad. When one of your power supply rails has a different voltage than the other funny things can happen to the amplfier. This can happen if one of the main storage caps is failing. When you turn off the amplifier the storage caps keep suppling power to the circuitry in the amp until all of power stored in them is used up. If one of storage caps is failing it will have a lot less energy stored in it and will be exhausted first which can result in a voltage imbalance on the differential input. This can cause the funny noises you hear when the amp is powering down. The noises are probably the amp oscillating because of what is happening at the front end.
 Of course this is only a hypothesis and something else may actually be going on.
Good with your trouble shooting.
Scotty

I don't think it's a bad cap due to these being two mono block amps and the sound happens in both speakers

[DaveC113]

I'd probably double check all electrical connections you can, in the box and at the ground rod. You could check to see if both of your 20A lines have the same ground potentials at your components, it's pretty important that it's minimal, with longer runs it can be an issue which is why tying the power distribution blocks grounds together is a good idea. I think, but am not 100% sure that bonding grounds together between circuits within the home wiring is not to code but if it's done using power distribution boxes it seems you can sidestep that issue. Or as I said just run the entire system on one line and see if the noise is still there.

These kinds of problems can be frustrating, good luck! 

[Folsom]

The first thing I do when I hear hum is wiggle cables. Broken cables can do this, or having hot/ground mixed on something that is DIY.

Maybe it's just coincidence, with the rain?

[jmdesignz2]

The first thing I do when I hear hum is wiggle cables. Broken cables can do this, or having hot/ground mixed on something that is DIY.

Maybe it's just coincidence, with the rain?

I checked the dedicated lines and I am getting 119 V on one line and 120V on another
Could this be a clue?
Previously, it was 119V on both.

This was checked from hot to neutral and from hot to ground to see if there was a difference. There was not. Shouldn't this mean the grounding is OK?

However, I went outside and found the ground rod. It's a piece of rusty rebar very corroded. Unknown length. The copper wire is still good though.
The old telephone system is grounded about 40 feet away around the back of the house to a piece of galvanized pipe that runs into part of the concrete poured patio area.
The telephone system is Not used but I cleaned up that ground and there was no change.

I purchased two new copper plated 8 ft ground rods and will install those sometime this week.

I still am very concerned about the Loud buzz noise that the speakers make when the amps turn off. It's the same in both channels. It's quite loud- kind of like a large bumble bee / large winged grasshopper but metallic, slower in cadence and has static noise. It rises, falls and diminishes in about 2 seconds. These have NEVER made this noise before. I unplugged all devices from the 2nd dedicated outlet and the noise is still there.

[Bob2]

Have you tried a floating ground to see if the hum goes away?