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Glow Audio Amp One Hum

post #1 of 27
4/25/09 at 4:39pm
Thread Starter 
THis is my first tube amp for headphone use. I purchased this after reading the 6moons review (blue Moon award). In that review the Amp one was described as being extremely quiet. I am impressed w/ the build quality, great paint, solid as a brick and point to point wiring w/ good soldering.

My set up: Grado GS 1000s, Cambridge audio 840CDP, and Signal cable silver ref interconnects.

I love the sound except for the low level Hum. It is not bad enough to stop listening but is eaily noticeable especially at low volumes. I replaced all 4 tubes w/ Mullards and the hum was still there.

Any Glow Amp One users out there to comment?

Is this just the nature of the amp or could I have a bad amp?
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post #2 of 27
4/25/09 at 5:01pm
Thats why people buy solid state.
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post #3 of 27
4/25/09 at 5:09pm
Had it just occurred recently or did you have the humming since the beginning?
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post #4 of 27
4/25/09 at 7:56pm
Thread Starter 
The hum has been since day one when the amp was new and persists after about 50 hrs use. I tried a good ps audio line conditioner and different AC outlets with no change.

I am wondering if this is just the normal amp operation and headphones are sensitive enough to exploit the hum that otherwise would not be heard w/ average efficiency speakers???

I've not used many tube amps before so am not sure if a little hum is par for the course.
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post #5 of 27
4/25/09 at 9:54pm
I have no hum through speakers, but have recently sent back my "last year's" model for repair of the headphone jack. Do you have the new one? Is the problem only on the headphones?

- Ed
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post #6 of 27
4/25/09 at 10:10pm
I had it for a while and loaned it to another head fier. He heard the hum but I did not, hope you can get it sorted out. I thought it sounded quite good as a headphone amp.
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post #7 of 27
4/25/09 at 10:13pm
The problem is that you are using an OTL tube amp with ultra-low impedance headphones. This will result in some hum in the majority of cases. That particular design definitely has the track record of humming with low impedance cans.

If you tried something like the Senn HD650 of the Beyer DT880/990, you'd probably have no hum. I'm not suggesting you change headphones, mind you, just pointing out what is causing your problem.

It has nothing to do with the sensitivity of the headphones - it is the low impedance of the Grados that is the issue.
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post #8 of 27
4/26/09 at 6:25am
Thread Starter 
Thanks for the comments all. I do only hear the hum w/ headphones. not on speakers.

I gota email response from Glow and they said others had reported the hum w/ headphones. this may be normal for this amp and not a problem w/ my amp. knowing this I will likely get another amp. I read the Zana Deux is worth the wait.

We'll see if it is the low impedance Grados b/c hopefully my HD800s wil arrive soon.
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post #9 of 27
5/4/09 at 6:33pm
Quote:
Originally Posted by Skylab View Post
The problem is that you are using an OTL tube amp with ultra-low impedance headphones. This will result in some hum in the majority of cases. That particular design definitely has the track record of humming with low impedance cans.

If you tried something like the Senn HD650 of the Beyer DT880/990, you'd probably have no hum. I'm not suggesting you change headphones, mind you, just pointing out what is causing your problem.

It has nothing to do with the sensitivity of the headphones - it is the low impedance of the Grados that is the issue.
The Glow one amp has output transformers so it isn't OTL. Unless, it functions as an OTL amp for headphone use and only uses the output trannies for the speaker outputs.

http://www.glow-audio.com/i/srajan%2...s/srajan_6.jpg
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post #10 of 27
5/4/09 at 9:02pm
I am almost certain I read that it is OTL for headphone use.

In looking, I did read this on the Glow website - YIPES:

Quote:
*POWER TUBE INFO: European EL84s differ in design from their Chinese and Russian counterparts in one important respect: On all European manufactured EL84s, pins 1 and 2 are connected together inside the tube envelope. Chinese and Russian EL84s do not internally link the pins 1 and 2. Therefore, when a European manufactured EL84 is plugged into the '09 GLOW amp, the additional connection within the tube envelope in the European design is likely to cause premature failure of the tube.
For the above reason, it is highly recommended that you NOT use European tubes in the 2009 Amp One, as you will likely permanently damage your tube and possibly the amplifier. All Russian and Chinese manufactured EL84 tubes are compatible with the Amp One.
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post #11 of 27
5/4/09 at 9:59pm
Quote:
Originally Posted by Skylab View Post
I am almost certain I read that it is OTL for headphone use.

Aah. I see.

In looking, I did read this on the Glow website - YIPES:

Yes, I had the same reaction when I read that too.
...
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post #12 of 27
5/4/09 at 10:25pm
Quote:
Originally Posted by triode12 View Post
Yes, I had the same reaction when I read that too.
And it's due to a poor design. I have 2 amps that use 6BQ5/EL84's, that do not have this problem, and I have owned several others, again without this problem. Restricting this amp to Russian and Chinese EL84's is really handicapping it, since neither sound very good when compared to the awesome sounding US/Western European vintage versions (I am assuming that the US 6BQ5 would be as much of a problem as the European EL84's).
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post #13 of 27
5/5/09 at 6:44pm
Hmn, wonder if that caveat applies to the 2008 version. Will have to give Patrick a ping to find out.

Anyway, I got my 2008 modle back from Audiomagus yesterday. They repaired the HP jack - no hum I can detect. The DAC is significantly improved by the rewiring associated with the upgrade - less "shallow" and good bass. Also very clean.

- Ed
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post #14 of 27
5/5/09 at 10:28pm
No it does not apply to the 2008 version. I had one and as a matter of fact I bought a pair of 6BQ5 tubes from Skylab to use in the 2008 Glow I had. BTW I don't believe the 2008 Glow is OTL.

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post #15 of 27
5/6/09 at 11:45am
So perhaps the Glow is not OTL with headphones. Maybe someone at Glow can comment on that. But that makes the OP's problem more troubling...
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