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Hello everybody, I need some advice on reducing the very annoying hum coming from my new pair of Avantgarde Uno connected to a pair of M60 Mk2.2. monoblocks. These are connected to a MP3 preamp through balanced connection.Hum is present even with the pre switched off.
I know it could be some nasty ground loop, and I tried then disconnecting the ground pin in the preamp power cord, and the ground pins in the subwoofers cords as well. No result in both cases, hum is still present.
There is more then a ground loop? Maybe an “intrinsic” hum (and some hiss too) in the M60s? Too much gain? I remember someone in the old board reporting his great experience with the same combo. Anybody else has had similar experiences with high efficiency speakers and A-S OTLs?
Any help would be greatly welcome.
Cheers,
Follow Ups:
We have found that some older M-60s have issues with electrostatic sheilding that does not show up until you try to drive horns. The solutions are fairly simple; but if not a tube the unit might need some minor update.
Thanks for the hints Ralph; I'll contact you directly.
I've been using M60's/ MP-1 with A/G duos all balanced since 2000. I have two suggestions for you. The first addresses the innate sensitivity issue of your speakers when paired with M60's.
I suggest you proceed with removing V2 after obtaining the properly shorted replacement tube socket from Ralph made especially for this purpose. This will reduce the gain of your amps significantly [don't worry, you'll still have beaucoup drive for the Unos]. Just make sure to check DC offset and bias for any changes and correct accordingly [their values remain the same].
Secondly, unusual levels of hum can be an indicator of a less than optimal/failing power tube or driver tube. I would suspect this to be a more likely in a scenario in which there seems to be a relative imbalance between the amount of noise you're hearing from one side to the other [i.e. one side is louder/buzzier than the other]. Ob viously a tube tester capable of measuring octal tubes will be required to perform the necessary checks although visual inspection of the power tubes for ouright shorts can be performed at home by eye as outlined in the Atmasphere website. Failed or failing tubes are also generally indicated when the extremes of range in the set screws to adjust DC offset and bias have to be brought into play in order to accomplish these settings [or if they cannot be achieved at all].
But I would look to pulling V2 first. It's the driver tube [6Sn7] on the right front as you face each chassis. Just pull, sustitute the socket you get from Ralph, turn it on and I think you'll experience immediate major relief. Warm it up and them check your adjustments and you're done [hopefully].
If curious you can check out my whole system on the asylum under this moniker.
Good luck!
How is the DUO driven by the M60 Mk2.2? Does it sound bright and not enough body? I've the Wavac811A driving the DUO. I love the sound of the Wavac since it is so smooth and full body. I"ve heard that the M60 can sound very transparent but light in the bass. Can you describe the sound of your system with the M60 driving the DUO in details? Thanks.
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