Hello,

I've had an Outlaw 7700 for about a year. I'm using a Denon 4306 as my pre/pro and it lacks differential (balanced) outputs. So I'm stuck using single ended (RCA). I've been fighting with a ground loop and associated hum for the entire time I've owned this amp.

My ground loop mostly goes through my TVs grounded power cord, over an HDMI cable to my pre/pro, over the RCAs to my amp, and back to ground by the amps power cord.

I read somewhere about the Ebtech HumX device. It claims to break ground loops without interrupting the ground. You put it in the power outlet and then plug the power cord into it, just like a typical ground lifter/cheater but this device has some circuitry to leave the ground intact but block ground loop current. I'm not sure how this magic works.

So, I'm thinking about trying this on my 7700's power plug. Is this a good idea or a bad one? Anyone have any experience with doing this? What are the advantages and disadvantages of this approach?

Thanks!
Dan

dgilley,

It sounds like the hum originates at the TV. You might want to try a simple test. One of the most common causes of ground loops is cable TV. They are on a different ground than your home and so the loop is induced. If you have cable unhook it and see of that is that eliminates the hum. If so, there a number of products (Jensen Transformer makes a simple inline ground breaker you put on the cable) you could try.

If that does not work then the Ebtech might be the answer. Before I spent a bunch of money I recommend you spend some time unhooking everything in your HT and then hooking it up until you get the hum. That process will help you ID the cause. The other day in the Saloon a Gunslinger reported a problem with some outside lights that induced the hum. Ground loops are frustrating but usually can be solved after some detective work. Let us know your progress.

Thanks AvFan.

I agree that the TV, a Samsung 67" 1080P DLP, is a big part of my problem. But I have nothing connected to it except power and the HDMI cable going to my Denon 4306 that I am using as a pre/pro. I don't have cable, although I do have satellite RG6 lines run into my sat receiver, a DISH VIP622.

I have previously gone through a full ground debug exercise of disconnecting everything and starting at my amp and working my way backward adding things to find when the hum starts. At that point 90% of the hum was due to the loop through the TV even with no cable connections. But its been a long time and I've made a few config changes to my system so I'll do it again.

I'll post results. I also ordered one of those Ebtech HumX widgets so I'll try that at out as well and post the results.

Right now all my gear is connected into a single Brickwall 20A audio surge/distribution rack mount. But if I can't solve this hum problem through some simple measures like the HumX, I'll have to buy some more expensive filter/conditioner or whatever it takes.

At this point I'm so frustrated I'll spend just about anything to make it go away. GRRRRRRRR

This problem would have been solved for the future for everyone if the HDMI inventors had instead choosen an optical connection rather than electrical, since optical maintains "galvanic isolation". Fiber optic cables have the nice benefit of providing electrical isolation so no ground currents or other noise of any kind can pass over the cable. It would be a great thing to have a system built with nothing but optical connections between all units for data movement until the final high quality analog-to-digital conversion, at which point the signal path to the amp should be differential (aka balanced). A system designed this way would be VERY noise immune. Oh well.

Thanks,
Dan

p.s. - Outlaws, if you had an HDMI switching pre/pro with conversion of the analog inputs to HDMI I would dump my Denon 4306 on ebay and buy it from you immediately. To get the differential outputs and help solve this plague on my existance . . .

dgilley,

Just a couple of thoughts...Is all your HT gear on one circuit? Is it possible that the ground could be different for multiple circuits? If you have two or more I'd start looking at connections at switches and wall plates. Also, are there any motors (refrig or freezer), dimmers, timers, or other noise generators on the HT circuit(s)? I had an electrician friend tell me to be wary of aluminum wire since it will loosen in the connection over time. If all else fails it might be time to call an electrician to diagnose the problem.

I agree those would all be potential sources of trouble. I have my entire system on a single 20A dedicated circuit. The only thing plugged into the 20A circuit is my Brickwall 20A surge protector which has 10 outlets arranged in 5 "isolated" banks of 2. My amp, prepro, tv, dvd player, and sat dvr are plugged into the Brickwall. I've mixed around the various devices into different outlets on the brickwall to minimize the hum but it doesn't go away. And all the wiring is copper. This is a very new house hence it has no aluminum wiring.

Maybe an audio power specialist could help me but I kinda doubt calling an ordinary electrician would help. I wouldn't let any electrician I've ever met even touch my AV system!

Thanks for all the ideas AvFan! I'll keep working on it . . .

Do you have a phone line connected to you satellite receiver? If so, have you unplugged it? I had a hum that was cause by my cable connection as well, but I'd guess anything that isnt properly grounded might have the same effect.

When I hooked up my 7700 I had the that terible hum. I went crazy looking for it and I have two Monster cable surge protectors. The 3600 and 3500. I also have comcast cable.

AvFan had a good idea about disconnecting everything and then reconnect to get the head of the problem.

My situation called for a dedicated 20 amp circuit for the 7700. Once I did that my system was quite as a mouse. I really had no other options since I had eight outlets on two 15 amp circuits and was running a lot of equipment. Not a hell of a lot of amps but enough to cause that HUM.
If you are still having problems as I am writting this try running a new electrical line.
It is not hard to do as long as you have easy access to your walls

I just picked up a 7700 and have the dreaded hum. I am going crazy trying to figure out the source. I am getting dazed and confused unplugging everything trying to find the source.

Here is my AV Setup;

Denon 3803 (now acting as my pre-pro, Sony DVD Jukebox, Sony CD Jukebox, DirecTV HD Tivi HR 10-250, and a Bang & Olufson Turntable, all connected to a Monster Power 2600.

This is on a dedicated 20 amp circuit that is also connected to another outlet feeding a Sony 60 inch SXBR LCoS and a 250 watt Def Tech sub.

I tried unplugging the satellite cables and I still have the hum. I unplugged the phone form the Tivo, still get the hum. I unplugged the TV and sub and still get the hum.

When I swith the Denon from the Tivo to the DVD player, the hum goes away as the Denon switches input sources, but then reappears after about a second. If I turn the volume all the way down to nothing, the hum goes away. But if Iturn it back up just one click on the volume knob, the hum reappears.

Today, I unplugged one of the RCA cables going from the Denon preout to the input on the amp. I disconnected it at the amp. The hum did go away from that individual speaker. So I tried disconnecting another RCA cable going into the "input" on the 7700, and the hum went away from that individual speaker.

If I dont solve this soon, I will go nuts! Does the Ebtech HumX really work, and will I lose any hi current draw capability if I buy one?


BTW Running another circuit is just about impossible. I know how to run circuits, but this would require a pro and I ma not spending $500 for another line.

PS; I am using Monoprice RCA cables. Here is a link to them; http://www.monoprice.com/products/produc...format=2&style=

Or would these be better? http://www.monoprice.com/products/produc...format=2&style=

Those pesky ground loops will drive you crazy! I assume you didn't have the hum until introducing the 7700 so maybe you have a cable issue. Do you get the hum from every speaker and is it at the same volume? If the hum is only in a one or two speakers you might have a cable issue due a bum cable. However, if the hum is the same in every speaker it is more of a system issue. By that I mean a single source is probably the problem. It doesn't sound like it, but you might have a noisy electrical environment near your equipment too. Do you have any other electrical devices located nearby that could induce a signal in the RCA cables between the Denon and the 7700? This is kind of a longshot since your cables use RG6 coax.

I'd start by unplugging everything and then plug in the Denon and then the 7700. I'd try this with and without the Monster 2600. If the hum returns at that point you narrowed the issue to those two components and a call to Outlaw may be necessary. If not, keep adding components until the hum appears.

One more thing: does the hum occur day and evening? There was a Gunslinger that had the hum in the evening but not during the day. It turned out it was a bad switch or fixture used to light his backyard at night on a separate circuit that induced a hum in his gear.

Keep the Saloon updated on your progress.

I get the hum/buzz in all 5 speakers, and my guess it is at the same volume. I cant think of any other electrical devices that are close to my AV gear.

I have already tried unplugging the sat video cables, but I still have the hum.

Are all high power amps this finicky?