Help with diagnosing a hum

[SBranson]

Coming from iems and daps back to headphones. Currently have Abyss Diana Phi and a Woo Audio WA7 gen 3 dac/amp.

Overall the sound is excellent. There is however a low level hum coming from the amp and audible through the headphones. I know it’s a tube amp and always figure there is some noise but I also figure it should be quieter. Maybe it’s something I have to live with… but here’s what I’ve tried.

- It is not reactive to volume
- I’ve tried different tubes but no change
- I have an older Foundation Research LC-1 Line conditioner I hoped would help if it was ground loop or EMI. It is better. It not gone
- Audiophile outlet from 20 years ago back in my 2 channel days.
- ferrite bead just to see but no real sense of any difference
- No effect touching plugs or chassis
- Got a Nordost USB cable but doesnt eliminate it and further there is no change if I unplug the source.
- Tried disconnecting the ground wire in the outlet just to see but no change.
- Took it to another room in the house and it seemed worse there.

**edit**. Source is a Samsung tablet. There is no computer in the room. This is my den without any other electronics except my iPad. The router is on another floor.

My next step is to buy an iFI DC blocker and see if that‘s the issue. Only reason I haven’t is because, one, it’s another $200 and two, I keep reading that DC issues are isolated to the component and not audible through headphones/speakers.
I haven’t taken it to anyone else’s house as unfortunately there‘s no one close by to try that.

Unfortunately if it’s a problem with the amp, I can’t find out without shipping it back to the retailer half a country away. I’d hate to do that, have it tested and it turns out it’s something wrong here.

Any other suggestions?

 

[bigshot]

Try using another source and see if it changes. I'd notify the seller that you are having problems. They may have a suggestion.

 

[SBranson]

Try using another source and see if it changes. I'd notify the seller that you are having problems. They may have a suggestion.

Thanks for the reply. Considering that it's there regardless of the source actually being plugged in I don't think that's the issue.

I contacted Woo Audio and they were courteous but of course couldn't really suggest much beyond contacting the retailer for warranty issues. As I mentioned, that'll be a $60-80 shipping bill for what might turn out to be something that isn't a problem with the amp.

I guess I'll bite the bullet and try a DC Blocker and hope that either solves it or mitigates it enough that I can just learn to live with it. It's not bad and there's actually been times when I wasn't sure it was there but there are evenings where I can hear the hum from my chair with the amp about 3-4' from my ears. It's like when you first notice the sound of fluorescent lights and then you can't unhear it..

 

[bigshot]

I think you’re throwing good money after bad. There is something wrong with the amp. Did it ever work?

 

[SBranson]

I think you’re throwing good money after bad. There is something wrong with the amp. Did it ever work?

Hard to say. When I first got it I thought it was quiet just with my regular plug and a very cheap power bar but then I changed the power bar to an old Monster Power one and everything seemed noisy. I got rid of that and it really got a lot quieter but it's still there a bit.
I guess the only real thing I haven't tried is going all the way back to changing back to the $2 outlet and the $8 power bar at the very beginning. I just feel that I got more critical as time went on. Further, the hum became apparent to me when I got some high impedance earbuds from a friend of mine who makes them and he suggested I use the amp as they seemed to respond better to more power. That's when I first noticed the hum and then when I went back to the Dianas, I realized it was still there.
I figure I just didn't notice it before.. exactly like my analogy to the fluorescent lights that you don't notice until you do and then you can't un-notice.

Again, the main worry about sending the amp is the $160 round trip and 3 weeks if it turns out to be a problem at my end.

 

[bigshot]

Your problem appears to be some sort of grounding issue. Forget the fancy power plugs. Go with what works.

 

[SBranson]

I'll try the original set up tomorrow after work. I suspect it won't fix anything as I figure the wiring in my house is a mess and probably the problem.
But at least I will know.

Thanks

 

[bigshot]

Unless you are plugged into the same circuit as a refrigerator or an AC unit, it shouldn't be the house wiring. It most likely is some expensive piece of audio equipment that doesn't play nice with others. Buying more expensive esoteric audio equipment won't help that. You shouldn't need all those line filters and power conditioners. A good ground should do it.

 

[bigshot]

Wait a minute... the amp is making the noise in the room? It isn't through your headphones? You can hear the amp itself from 4 feet away? If that is the case, it is 100% a problem with the amp.

$160 just to ship your amp back for service? I would be on the phone yelling at the company that sold me something with that kind of deal. Man! Next time buy from Amazon.

 

[SBranson]

It's both. I can hear the amp and I can hear it through the headphones.

As far as the wiring.. The house was built by the owner and out where I live there was some suspect activity in terms of some illegal building and such. There are a few cases of weird wiring in this house. I'm right above the kitchen and when the microwave turns on I can hear the hum. Not sure if it's outside the headphones or through the wires because with open headphones it's almost impossible to tell.

But yes I can hear the amp very subtlely but it's obvious there was noise once I turn off the power..

 

[SBranson]

$160 just to ship your amp back for service? I would be on the phone yelling at the company that sold me something with that kind of deal. Man! Next time buy from Amazon.

I figure the $160 is to ship it back for warranty and likely having to pay for shipping it back to me if they discover there's nothing wrong and it's my stupid wiring.
That sure is the beauty of DAPs.. battery power for the win.

 

[dunring]

Do you have an outdoor 3 prong grounded extension cord to run it to an outlet on a different circuit breaker just to narrow it down?

 

[bigshot]

And take it over to a friend's house to see if it hums there. I tend to doubt it's your house, unless all you need is a good ground. And that costs nothing.

A warranty that costs $160 isn't a warranty. Don't buy that brand ever again. I would be yelling if the retailer told me to talk to the manufacturer and the manufacturer wanted to charge me $160 for their mistake. I'd demand a return for a full refund.

If an amp makes a humming noise that you can hear without even putting on headphones and hear it from 4 feet away, it is defective. You shouldn't lay down and let them take advantage of you like that.