Well - I had a dreaded hum that I temporarily fix with a 2 prong (3 to 2)..but although it eliminated it - its not the way to go in fixing the hum - dangerous I hear...Most of us know that a ground loop hum comes from - at most times - your cable line...sure enough for me it was. What I did was add a cable ground block radio shack and then took a ground wire (I had an old lamp lying around that had a ground wire that I removed), then I put the ground on the block and then unscrewed a little my wall outlet (that is grounded) and wrapped the ground around the screw and tighten it up - and now the HUM is completely gone..I read this somewhere by some guy at AVS..

Hello,

I just hooked up my new 7700 today and I am so disappointed! Major hum. Present all the time and audible over low volume parts of music. Really bad - definitely not tolerable. While the amp sounds great, I can't take the hum so it must be solved or I'll have to return the 7700 and go back to my Denon 4306's built-in amp which had ZERO hum. Of course, the Denon had no ground prong on its plug! Maybe their solution to the hum problem??

Things I've tried:
- disconnected all cable, phone and network connections to the system. didn't fix it. I take it when you disconnected your cable system it went away, Chi-town? Doesn't seem like my hum is coming from the cable system if its still present even when disconnected from cable.

- disconnected RCA signal inputs jacks to the amp and the hum went away (this was the only zero hum configuration with the amp powered on)

- disconnected all other devices from the power outlet except the amp but left the RCA jacks connected between the preamp and amp. The hum was there!!! How are these other devices causing a ground loop without being connected to ground!?!

Note that this is a dedicated 20A circuit hence there is NOTHING else on this circuit except the amp. And I still get hum when the RCA jacks are connected.

Another interesting observation is that the amp itself hums when the speakers hum. Its like the whole thing is resonating at the same frequency as the speaker hum.

Also, when I put a 3-to-2 prong power adapter plug (thereby disconnecting the ground) the hum is gone. Is this actually unsafe? Is this a bad long term fix? If so, why? The Denon doesn't even have a ground pin.

I'm so sad and worried I'll have to return this beautiful beast. And I fear having to lift it back into the box!

Help. Please. Anyone.

Thanks
-Dan

Well, you are not alone. I finally got the chance tonight to hook up my new 990/7500 combo and I have spent the last three hours trying everything to get rid of the hum. It is equally as bad as you described.

I just tried the same plug adapter solution you used and the hum is gone, but I am pretty certain this is not a good fix for either of us. On the other hand, I least i can go to sleep now.
Ed

When I had that problem (discussed in this thread) I called outlaw and spoke with Steve and then Scott.
Scott said to send it back for exchange. I told him thanks, but the amp is fine (I decided fine because dead quiet otherwise with no inputs)...and I tried the cheater.

My system runs dead quiet, except when my wind-turbine is really cooking (generating power and feeding grid). Some of our digital clocks also speed up, so I'll have to accept this. Only occurs when generating in excess of 10 kW/hr, which is usually at around 150 RPM and wind speeds in excess of 20 mph at 120' above ground. Actually I wrote about this, but I'll ask for ideas on filtration in another post.
Ideas appreciated.

Don't send it back. Try balancing some channels.

Dan,
I also had similar and significant problem with Hum. I'm not sure what your using as a Pre/Pro but I have the Outlaw 990 that takes either RCA or Balanced Cables. The problem was definitely related to using the RCA cables in the system, and was gone completely when I replaced them with Balanced Cables.

Thanks for the comments everyone.

Jim, I have a Denon 4306 as a pre/pro. So no differential output option. And its too nice a pre/pro (brand new and state of the art) for me to consider ditching it yet. I understand why the differential interface of the balanced cables solves this hum problem. Differential interfaces have a shield connecting the grounds on either side and that shield can carry current without affecting the data content of the interface since the data is decoded by comparing the differnece between the plus and minus signals. In a single ended interface (RCA) the signal is obtained by comparing the single signal with the ground. So if current is flowing on that ground between the two unit grounds on a single ended interface like RCA you get hum (a time variant voltage offset). So your setup still has a ground loop and the current is still flowing. You just can't hear it with the differential interface. Which is good (sorta - it would be better to get rid of the ground loop).

So, my progress!
First, I applaud the outlaws, Steve specifically, for reading this forum and sending me an email a few hours later on Friday night without me even having to contact their customer service! BRAVO! Amazing service.

I ended up taking a systematic approach to find the worst offending cause of the hum in my system. I took EVERYTHING apart and started at the beginning with just the amp plugged into a single 20A power circuit with NOTHING else on that circuit. No hum. Then I added connections to my pre/pro via RCA with nothing else connected to the pre/pro and with it plugged into the same power circuit. No hum. Then I started adding devices to the pre/pro, one at a time, plugging them into the same power circuit and connecting them to the appropriate pre/pro inputs, until I heard hum. And I found where 90% of the hum was coming from. Whenever the HDMI interface between my pre/pro and my TV was plugged in, I got huge hum. Otherwise the system was pretty darn quiet and within my tolerance.

My dang new Samsung 1080p DLP TV! Its a HLR6768W (very nice TV). It has a grounded plug and was plugged into an outlet on another circuit on another wall due to power cord length. And after adding a ground bypass plug to the TV power all the problems went away. Bingo. I am 90% sure I have found my ground loop. The ground current was flowing between grounds on these two power circuits which were at slightly different potentials. The path was from the 20A circuit outlet into the 7700 amp, over the RCA cable shields to the pre/pro, over the HDMI shield/grounds to the TV and into the 15A circuit outlet. BUZZZZZZZ! But no more.

I suggest this approach to others who are having this problem. You CAN find the ground loop current path and that is the first step to eliminating it.

So now to find a better permanent fix than bypassing the TV's ground plug. I bought an extension for the TV power cord today so I can plug it into the same circuit as the amp. Hopefully that will reduce the ground potential offset to an inaudible level without having to bypass the TV's ground pin.

I'll let you know!

By the way, I LOVE the sound of this new amp. It sounds beautiful with my Paradigm Reference Studio 100's. Really dang sweeeeet.

-Dan

Well I am glad to see that I have company. I purchased the 990/770 a couple of weeks ago and Tuesday was the first that I had time to work on it.
Right off the bat let me take my hat off to Steve for giving me some ideas as to locating the HUMMMM and for being patient.
I disconnected the cable line and I still had the HUM. Then I checked all of the balanced cables one at a time. Still had the Hum. Then for the third time and I checked all connections to make sure that I did not miss anything. Still had the Hum. The final step as suggested by Steve was that I run an extention cord to an outlet that was not on line in my Home Theater.
Connect this line to the 7700. Turn it on and see what happens. BINGO!! No Hum.
My friend and I added up the wattage of all the equipment that I have even though we knew that I would never be using all of them at the same time or even to there max output. The formula is Amps=watts divided by Volts. The result was that with all the equipment that I have there was not enough amps to handle it and the result was the HUM.
I decided to run three more seperate lines into the room. I have two line conditions rated at 1800 watts max along with the 7700 at 1800 max. that is approx. 5400 watts right there. Not to mention the other equipment. I spoke to a certified electrician about the problem and he told me that if I wanted piece of mind to install the new outlets. Overkill? I do not know. What I do know is that I have no HUM.
Also if I decide to have any additions to the equipment I won't have to worry about the dreaded HUMMMM!!!
I do not know whether or not you guys are thinking about going threw the process of installing additional outlets on seperate lines but I thought you would like to know about a lasting cure.
Thanks for reading.

rubbersoul wrote:

I do not know whether or not you guys are thinking about going threw the process of installing additional outlets on seperate lines but I thought you would like to know about a lasting cure.

When setting up my equipment and moving from 2 channel stereo at 155 W/ch into at first 200w x 5 (outlaw 755) and then 200w x 7 (model 7700) I added two new runs of 20 amp circuits at the 5 x 200 watt stage. I think a good idea is to plan ahead. You never know what you're going to add in the future. In fact we added a big 60 inch Sony HDTV and then there was the LFM-1.

Also did some low voltage separate conduits from one location into living room for other signals.

Glad I thought ahead (at least this time

I have been feeding my rack with "2 prong" 230V for many years now, and I've always ran lots of kit (the pile emits real heat!) and my family's still alive I'm happy to report...
I don't know the US situation, but here in Holland the builders often bore the ground rod only 2m deep, which is NOT a good low resistance earth at all, this leads to stray voltage across the earth connection.
What I mean, it's better not to use earthing at all than use a faulty earth...
OF COURSE THE ONLY REALLY SAFE WAY IS HAVING A GOOD EARTH AND EARTHING YOUR GEAR !!!
Barend