Woo Audio WA6 - Hum Help Please!

[Weiszyn]

Hello

I recently purchased a second hand WA6, it is my first tube amp, I noticed that it had a bit of a hum coming through the headphones, its mostly only noticeable when my playlist has finished, its still there when playing music but I have to really try and hear it to notice it.

With the stock tubes the hum is louder, when I switch to the second set of tubes the seller was using ( RCA - 13DE7 x2, Philips GZ34/5AR4 - rectifier) it reduced the hum a noticeable amount, I think it was only the rectifier that caused the change in the hum volume.
When I use the Ohm switch at the back it changes the hum sound noticeably ~ the hum present when I'm using the 100-600 Ohm switch is maybe 2-3x louder than when I'm using the 8-100ohm switch.

If I take the WA6 to other power sockets(which have nothing else attached) in the house and only plug the AMP in with a pair of headphones the hum is present so assumedly its not caused by the source chain.

I have tried out some tech to see if they would help.

All from the Ifi brand

• DC Blocker
• GND Defender
• AC iPurifier
• Groundhog+
• PowerShield VoltGuard AVR 1500VA (UPS) - all this did was create more hum if it was too close

If they created any change it wasn't really noticeable to me.


The Hum Changes depending on what headphone I'm using

Focal Clear OG = the hum is very noticeable.
Hifiman Edition XS = Somewhat Noticeable but nowhere near as loud as the Clears.
ZMF Eikon = Slightly more noticeable than the XS.
DCA Aeon 2 Noire = Gotta listen and try to hear it to notice it.

I've tried 3 different Power cables in case one was faulty

I'm using my PC to feed my Mojo 2 which feeds the WA6

The Mojo 2 was using USB to the PC but the WA6 was picking up some weird interference from inside the PC so I switched to Optical and it stopped this.


The seller said they didn't notice a Hum but if there was one it was barely noticeable.

~~

I've seen some reviews call the WA6 dead silent, so I'm wondering if anyone has things I can try/advice please? or do I just have to get used to it?

 

[MaxwellsEq]

If other people describe it as "dead silent" and yours isn't, you may need to consider it faulty. I don't know the amp, but google turned up a spec of 96dB Signal/Noise (no mention of weighting), which if true, is good. If all sorts of isolators seem to not work, the noise may be the amplifier itself, perhaps something's not quite right with the rectifier.

 

[Weiszyn]

If other people describe it as "dead silent" and yours isn't, you may need to consider it faulty. I don't know the amp, but google turned up a spec of 96dB Signal/Noise (no mention of weighting), which if true, is good. If all sorts of isolators seem to not work, the noise may be the amplifier itself, perhaps something's not quite right with the rectifier.

There is the odd review that says they hear a hum so I'm not sure if its just that the people who think its dead silent are using really hard to run headphones, I don't know enough about this stuff to know why some headphones seem to highlight the sound far more than others.
I saw one thread where a guy had bought this AMP brand new and it had a hum so he returned it and the 2nd one they gave him did the same thing but maybe you're right if there's something wrong with it I'm guessing it'll cost a pretty penny to fix, I can't really send it to woo the shipping alone would be murder, I'll try get used to it, thank you.

 

[MaxwellsEq]

I guess there's also variations on what people think "dead silent" actually is. There are standard measures for noise (on its own, not signal to noise ratio). If there are any published test results, they would be helpful.

 

[JSmith]

hum so I'm not sure if its just that the people who think its dead silent are using really hard to run headphones, I don't know enough about this stuff to know why some headphones seem to highlight the sound far more than others.

Based on the measurements here, low impedance headphones may well show an audible hum from this amp depending on level.


JSmith

 

[antcollinet]

What other components are connected in your system (Eg your source - or other components if this is part of a larger system with speaker amps etc). Is it possible you have a ground loop heading through the analogue interconnect into your amp?

Never mind I've just read your OP Properly. When you went to a different socket with nothing on the input, did you short each of the inputs (pin to shield) to eliminate any pickup on open high impedance inputs. Your experience with PC noise eliminated by optical connection does suggest a ground loop was present. It might be worth powering the mojo 2 from a battery bank, which would eliminate any possible common mode mains frequency from its power supply.