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.

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.

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.
Also, I'm using Vandersteen 2Ces so I can't look at the drivers.
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.
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
I tried disconnecting everything from the receiver other than the DNA and the hum is still present. The AV receiver only has a 2 prong plug. I can try getting the converter for the DNA to see if that solves the problem.
In reading over the counter point article, the DNA is the only component with 3 prongs. The DVD player, AV receiver and TV/Cable box only have 2. Even with the cable tv disconnected from the wall, the hum persists.
I stand corrected! Thank you so much Steve! I had disconnected the cable tv from the back of the cable box but when I pushed it back on its shelf, the cable was still in slight contact with the connector. I realized that if I removed the coax cable away from the cable box, the hum disappeared. Looks like I need to get a cable TV ground.
I just discovered that the coax for the tv was still in contact with the connector on the cable box. After removing it completely, the hum went away. Apparently, I need to get the cable TV grounding filter.
sorry about the double post...my 1st one didn't show up at first.
so that hum noise was THAT LOUD????
I had the same issue within my setup. It was humming because of the cable tv coax cable, but it wasn't that loud. Anyway, look for ground loop isolator. 1 example is the Mondial MAGIC(Mondial Antenna Ground Isolation Circuit) box. YOu can find similar products cheaper. I bought this one sometime ago.
Doesn't degrade the picture quality on my Hi-Def and the hum is completely gone.
I'd have to turn up the system fairly loud to not notice it.