Since purchasing my twin Velo DLS-3750Rs in July, I've been plagued with varying degrees of hum. The only way to minimize it was to connect the receiver to the subs using only the subs' L & R Line Input Jacks. Using a Y-Connector to L & R Inputs easily doubled the humming so I just ran with L Inputs till this weekend.

After finding in these forums that the problem is probably the CATV connection - something that I'd never heard of. I disconnected the cable from the system. Voila - all humming gone!

Luckily, this weekend I was able to talk to a cable technician who was doing a trouble call on our street & described my problem. He was well aware of this condition but couldn't help me then as he had another call - but he took my info. I asked him about 'Ground Loop Isolators' & he said that in rare cases they use them but they like to solve the problem at the source - their cable system. I'm still awaiting their call, ha!!

Being inquisitive, I then rigged a probe on a wire that I plugged into the third hole (house ground) of the wall socket. I touched numerous metallic points around my system including the barrel (shielding) of the TV Cable, all to no avail. Finally I touched the outside barrel of the sub Audio Jacks. Voila - the hum was gone!

I had some unused quality Audio Plugs so I soldered 4 of them so that the barrels only were connected to 4 wires (zip cord)with the center pins floating (not connected). I fashioned them into a harness so that all 4 wires were connected together with a probe at the other end. I plugged them into the 4 sub Line Out Jacks (that I don't use) with the probe connected into the house ground. Voila - the hum is gone! I'll temporarily use this until the cable company fixes it.

What is interesting is that twin subs' output is much greater now with both the L & R Line Inputs being used. My Audyssey Calibration has required me to drop the sub channel from 40 to 30 & it still needs to come down as it is now sitting at -11 db. Probably 25 will be close. The Velo default factory preset is 35.

Interestingly, I was at my old fart's garage band last night where my buddy has been plagued with a huge hum/buzz in his computer audio system (that we use for backgound tracks) for years. I had him disconnect the CATV. Voila - the hum is gone! He's calling the cable company today, ha!!

Tom
Comox, BC

Good that you could solve your friends problem too.

I also had this issue. Luckily for me my cable and electric service come into the house at the same point. I was simply able to take the main cable coming in and use a cable grounding block to ground it to the main ground for the house. Problem solved.

BTW, your setup looks great with the M22's on the Velo subs.

I would suggest checking the cable block where it comes into your house and verify that it is grounded to the house ground. If it is not run a wire to it and the house ground.

Tom, interesting way to beat the ground loop that you came up with. Yes, when you connect both the left and right line level inputs twice the voltage is fed into the sub amp and it sums them, resulting in a 6dB increase in level(a doubling of voltage is 6dB, compared to 3dB for a doubling of power). Note that this doesn't mean that the sub's maximum loudness capability is increased by 6dB; it remains the same, but a lower setting on the volume control is used. A similar result follows from feeding just one input, but increasing the volume control to let twice as much voltage in.

Jason:

Checking the ground at the cable block is a good suggestion; however, when I touched my house ground probe to the cable barrel (coax shield) there was no change in the hum, which surprised me. I expected that to work. Only touching it to the Audio Jack barrels made a difference. I'm still waiting for the cable company to call, ha! I expect that I'll have to call them. Meanwhile, the subs are running quietly now.

John:

After making some adjustments to my HT yesterday, I reran the Audyssey Calibration on my Denon AVR-891. After decreasing the twin Velos' volumes to 25 now, it gives a -7.5 db setting. So, starting out at a volume of 40 that gave -10 db with only the Left Line Levels attached, using both L & R Inputs has made a dramatic difference in the Velos' volume settings. I realize that the max volume will not chnage, but it is interesting that these two subs are putting out such good volume (according to Audyssey anyway) at such a low sub volume settings.

Interestingly, a Future Shop customer gave these subs a failing rating due to humming. He returned 2 of them stating they were obviously faulty or a poor design. I surmise that it was a 99% probability that it was his CATV connection.

Tom
Comox, BC

I heard back from my buddy who had the CATV hum problem with his computer/audio system. I guess that his dealing with our cable company was less than succewssful for some reason. Anyway, he bought the RCA Audio Cable Ground Isolator from The Source (former Radio Shack) & it solved his problem.

Interestingly, I tried the same gizmo in many different connection combinations & it did not work for me at all. My home brew harness described above works brilliantly so I think that I'll not bother with the hassle of dealing with my cable provider....

Tom
Comox, BC

Sorry, wrong thread

Tom Comox, BC

Today I went golfing with my buddy who had the hum on his system. I asked him what reaction he got from his complaint with the cable company. Customer Tech Service told him that they don't deal with nor fix problems like these so basically the customer is on his own. This seems to contradict with what the local cable technician told me in person as this condition was certainly known to him.

Thankfully the Audio Cable RS Ground Loop Isolator worked for him & my home brew harness worked for me.

Tom
Comox, BC