2. amps-preamps
  3. 1163870968

Loud Hum from DNA 0.5

I just had my DNA 0.5 serviced at McCormack Audio for a blown capacitor. Now that I have hooked it back up to my system, there is a loud hum in my speakers. This never occurred before. It doesn't occur if I unplug the preamp input cables and changing the outlet didn't make a difference either. I even tried another set of interconnects and that didn't make a difference either.

The preamp is a Yamaha AV receiver and it has no known issues. I have no other amp available to me right now to hook it up to verify that only the DNA 0.5 is causing the problem.

I'm hoping someone here can make suggestions. Where the amp is being used is not my primary residence. I use an integrated amp at my home and have no way of testing this in my personal system.

Thanks!
taylormade2
aball
2,018 posts
 
Sounds like a grounding problem to me. I would call McCormack and have them walk you through checking the grounds. I'd say it is chassis grounded and they left one disconnected off the power supply board when they reinstalled it.

Or it could be DC. Look at your speaker's woofers from the side when you hear the hum. If you drivers stick out during the hum (it will be obvious), then you have DC on the outputs. Call McCormack for this too.

However - was the Yamaha the same one you used with the 0.5 before the cap repair? I knew a Denon receiver that had pre-outs that hummed like crazy.... Pre-outs are not a top design priority in receivers.

Arthur
taylormade2 OP
19 posts
 
Thanks for the input. Yes, it's the same receiver used prior to the repair. The system was essentially untouched other than using the receiver to power the speakers while i was waiting for the repair. I guess I'll have to wait until Monday to call McCormack.
taylormade2 OP
19 posts
 
Also, I'm using Vandersteen 2Ces so I can't look at the drivers.
taylormade2 OP
19 posts
 
Also, I should clarify that the hum is loud enough to make the amp useless. And regarding the preout noise, prior to repair, there was no hum and prior to the DNA 0.5, the Rotel amp produced no hum.
stevemcx
166 posts
 
Hi Taylormade2 -

Sorry to hear about the problem with your DNA-0.5. I have no idea what work was done on your amp, but it seems possible that the factory updated the Earth / main-board ground path while doing the repair work. This would normally be a good thing, but it may have gone awry in your particular setup.

If the amp were "broken," I would expect to hear noise constantly, even with no input cables connected. You say that the noise disappears if you remove the interconnect cables, and this suggests a ground loop. Try "floating" the earth ground connection on the amp by using an AC "cheater" plug (3-to-2 connection adaptor). These are available at your local hardware store. In addition, if you have any kind of an audio connection to a cable TV video system, disconnect it. If the hum disappears, you have been dealing with a ground loop. For a more complete explanation, go here: http://www.altavistaaudio.com/hum.html

Good luck!

Best regards,

Steve McCormack
www.SMcAudio.com
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