HUM

maheeinfy · 1895

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Offline maheeinfy

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on: December 23, 2015, 11:26:21 AM
My question is not about a BH amp, but I am posting here looking for some help. Pls bear with me, I m new to this forum and tube amps.

I recently got a Wooaudio WA2 amp, new from wooaudio, and i am using it with Beyer T1 and few other cans.

It does hum through the headphones when volume is at 11' clock and hum only becomes louder from there.

 i did some testing to isolate the device in the chain that is causing this problem. I found that when nothing is connected to amp(except power), there is no hum.

However when i connect a DAC, there is hum thru headphones. Even with DAC turned off, there is hum(i tried output of Schiit Modi, Emotiva DC1, line out of Fiio X3ii  - each of them powered off and not even connected to my laptop). RCA cables i am using are from Schiit and Emotiva, so i think they are good quality.

I tried different power cable, wall sockets, even took the amp to friend's apartment for testing, and the result has been same.

I have been using Schiit Magni, JDS O2, few speaker amps from Emotiva for more than a year - none of them have any hum issues.

 I contacted Wooaudio and was told to upgrade cables, dac to resolve the hum problem. But I think the cables, dac are not the reason.

On other note, one of the 6080 tubes i received, i think is faulty. It gives out hiss on one of the cups on headphone, even at zero volume. When i switch 6080 tubes on the amp from left to right, hiss also switches on headphones

 My question - What could be the reason for this dreaded hum? i'd appreciate any help in resolving this. This is my first tube amp, and i havn't been able to enjoy it due to all these problems.



Offline JamieMcC

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Reply #1 on: December 23, 2015, 11:53:15 AM
No idea about Woo amps but you could try wrapping/twisting your rca input cables round each other and see if it  has any effect on the hum.

Shoot for the moon if you miss you will still be amongst the stars!


Offline maheeinfy

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Reply #2 on: December 23, 2015, 11:58:44 AM
No idea about Woo amps but you could try wrapping/twisting your rca input cables round each other and see if it  has any effect on the hum.
Thanks i will try that.
I just tried this...I removed all the input RCA connections from the amp. Then connected the left and right input of the amp with a single RCA cable(i think the apt word is 'shorted'). With this, there is no hum.

I don't know what that means, but thought i ll put it out there



Offline Paul Birkeland

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Reply #3 on: December 27, 2015, 07:39:38 AM
It does hum through the headphones when volume is at 11' clock and hum only becomes louder from there.
What's 11 o'clock?  Is that all the way up? 1/8 of the way up????

i did some testing to isolate the device in the chain that is causing this problem. I found that when nothing is connected to amp(except power), there is no hum.
Then the amp is working fine.
However when i connect a DAC, there is hum thru headphones. Even with DAC turned off, there is hum(i tried output of Schiit Modi, Emotiva DC1, line out of Fiio X3ii  - each of them powered off and not even connected to my laptop). RCA cables i am using are from Schiit and Emotiva, so i think they are good quality.
This sounds like a grounding issue.  Woo should be able to help you with this.


On other note, one of the 6080 tubes i received, i think is faulty. It gives out hiss on one of the cups on headphone, even at zero volume. When i switch 6080 tubes on the amp from left to right, hiss also switches on headphones
If this isn't intrusive with music playing, I wouldn't worry about it.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Doc B.

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Reply #4 on: December 27, 2015, 08:36:44 AM
Sounds like you have a ground loop. I would contact the manufacturer and ask them specifically if they have any suggestions for resolving ground loop issues. You might get a little more info from them on how to deal with the issue if you present them with that additional info.

This kind of thing puts us in a difficult position. We do our best to help our own customers. Presumably because of that people will tend to come to us to ask for help about non-Bottlehead products. The problem is that if we answer we will be viewed by some as denigrating the competition's product, though that is not our intention.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.