7700-Hum replacing 755 with no Hum...why

THis is a dusie and I read the thread below about hum. I got my 7700 yesterday and simply swapped it for the 755. So I removed the 755 and hooked up the 7700 with same exact connections and NOW I HAVE HUM. No hum with 755. Hum with 7700.

I called Steve at outlaw. He suggested the usual things, those that are described in the manual and have been talked about here. Got started late last nite and gave up (tired). I don't understand why I should have a ground loop hum now when I didn't before, and everything is connected identically. Audio and speaker wires not running parallel or near the AC. Two dedicated 20 AMP new circuits wired in for my 755 setup worked well. Also a third that was already there in the living room.

And yes: I tested the circuits with on of those yellow testers, indicating proper connections, neutral, hot, ground etc. And yes I disconnected the dishnetwork power plug and coax feeds. Even disconnected the phone line from the dish receiver.

Very frustrating. I think I need to start from scratch and "re-build" the system.

Oh yes: Steve said that "differential amps" (of which the 7700 is one) are different from 755.
What does that mean? Thanks guys.

I'm having a similar issue with my new 7700. Prior to buying the 7700 I used five M200's with my 990 and there was no discernable noise or hum at any speaker at any volume setting. After installing the 7700 I heard 60 cycle hum that was easily heard 10 feet from the speaker. Interestingly the hum only appeared on the two surround channels and the center channel, the two mains were quiet - I'm not using the rear surrounds just yet. After rolling out my equipment rack to check my wiring again I noticed that the hum was reduced about 90% but still audible if you placed your ear close to the speaker which probably indicates some kind of wiring problem that was caused by moving the rack. I ran out of time to look into the problem further but will get back to it this weekend and report what, if anything, I find.

mike

If it is like my situation you may find the noise gradually disapating and going away after 20-30 minutes. Mine seems to be related to my Sat coax input, hopefully the weather will be good this weekend and I can check the grounding on the dish.

I had read about your experience with the hum diminishing prior to receiving my 7700 but after moving the rack the hum did not get any quieter over time.

This hum problem seems to be a frequent subject in the 7700/7500 discussions. I wonder what the problem is....

I have a 990/7500 setup...I have no hum at all in my system (its been up for about 3 weeks now)....dead silence. I use a DIRECTV H10 hi-def receiver; also have a rooftop OTA antenna conected to this receiver. My house is old (1925) with variations of modern wire, romex, "knob and tube"; all my gear is connected to a couple of surge protectors (reasonabally good ones) going into a couple of outlets, tied to 15A breaker. All receptacles are three prong, though. It's weird why this problem is affecting some users and not others.

Great help from tech support (Steve and Scott) today. Suggestion was made to troubleshoot, thinking of possible ground loop. So at outlaw suggestion I temporarily "lifted" the ground by inserting a "cheater". Hum went away. Dead quiet.
Now I know that I don't want to delete the ground pin, nor does outlaw want us to eliminate the safety accruing from ground. This was just a test, but what a simple test to do.

So it proved what I thought all along, that the amp was OK. After that I changed some things around. No hum. Dead quiet. Will check it again in AM after it has had a good snooze tonite. I expect it will be fine.

I still don't know why I had hum (ground loop) but as usual I'm quite happy with the product, the service, and support.

My $.02

Yep, in spite of the occasional wart, Outlaw's service is very good. Even though I give them the occasional ribbing, I frequently recommend their gear because of the support aspect.

Cheers,

**UPDATE**UPDATE**

So I thought the hum was gone. Not quite. This AM I turned on amp after being off 6 hours or so. Slight hum, no matter what else was disconnected, so long as unbalanced between 990-7700.

SO.......I got out some old mic cables (XLR(F)-XLR(M). And as I posted elsewhere: **VOILA** no hum !!!!

There is one variable and that is that the amp had been on for an hour or so. I'll leave it off awhile and if the balanced connectors do the trick that's it.

However there is one wrinkle: Been using an EQ between 990 and previous (755). It's an Alesis DEQ830, which you can use balanced or unbalanced.
So if I want to use it I'll make XLR-TRS adaptors for it.....or....if outlaws tell me it's OK to try (and I'm waiting for 9AM to talk to Scott) I'll prefer (for ease and cost) to go unbalanced if they tell me I can do that and have a XLR-XLR balanced in to carry whatever reduces hum. This will be tried later this AM.

Tune in again and I'll write the results.
One thing to remember if you have hum: it's not the amp. These are absolutely dead dead quiet.

To add to my previous post (no hum-990/7500)-I am using Outlaw balanced cables...

jmcari wrote:

To add to my previous post (no hum-990/7500)-I am using Outlaw balanced cables...

Right-on. I just spoke with Scott and earlier Steve. They agree that this may eliminate whatever differences in potential to ground exists.

My system needs to go unbalanced, so I'm going to see if the balanced cable will carry whatever benefits accrue while unbalanced will make my life easier. For example I like an EQ between 990 & amp. Also I am going to be using KEF 107s and these use bass management (i.e. the KEF "CUBE") about which I'm just finding out. Will post results of balanced plus unbalanced later.

Followup info:
Seems like so long as at least one channel carries the balanced signal and the switch is set to balance that the amp is dead quiet....absolutely no hum.

Conclusion ground loops SEEM to be eliminated by at least one balanced run.

Opinions??

Experience ???

FWIW, my 7700 with XLR's is dead quiet. Even putting my ear up to the speakers I can hear no hum or hiss. I do get an occasional mechanical transformer hum from the amp itself but that is a separate issue with an interaction between my display and single circuit feeding all of the HT devises.

Wharg: My experience with balanced is same. Absolute dead-dead-dead quiet.

I wrote above that my system needs to be balanced because of the KEF 107 CUBE. OTOH, my DEQ830 which is a balanced EQ may sufficiently do the job instead of CUBEs.

The 7500 is on my short list of amplifiers. I look forward to the solution of this hum problem because I will not be using balanced inputs.

Rat wrote:

I look forward to the solution of this hum problem because I will not be using balanced inputs.

I would also prefer to not use balanced inputs, as it would simplify my life...interfacing with an outboard EQ, for example.

After solving your hum (probably ground loop)situation, please post the details of what it was and how you fixed it.

Run it by Steve and Scott
They were very helpful.

If it is any consolation, I had a similar inconsistent hum situation in my own comparisons last year of the Outlaw 755, Rotel RMB-1095 and Anthem MCA-50 amps. With exact cable swaps (using all unbalanced RCA connections), the Outlaw and Anthem were completely quiet, but the Rotel had a noticeable hum. The Rotel dealer suggested trying a cheater adapter to disconnect the ground -- not as a permanent solution. This made most but not quite all of the hum go away.

I am new to this forum.I hope someone can give me some valuable information. I am looking into purchasing a new amplifier. I was looking at the Rotel 1095 But have deceided to go with the Outlaw 7700. My question is if I am considering using my Yamaha 3300 Receiver as a processor (I am also thinking about selling it and getting the Outlaw 990) this HUM issue bothers me.I have no hum having everything grounded and using two surge protectors from Monster. If I keep my Yamaha I will not be using balanced cables rather monster interconnects. Of course if I go with 990 I will probably buy Outlaws cables as well. Does anybody have any thought as to what way to go with this new set up? Yamaha, keep it or sell it, balanced cables or interconnects?
Thanks,
Frank

So far the hum issues are related to ground loops, which are a risk no matter what hardware you use. Many receivers and source components aren't as susceptible to it because they don't use three-prong power cords, while big power amps typically do and are therefore often the trigger for ground loop chases. Unfortunately for them, they are usually not the culprit - cable TV is the primary source of ground loops, due mostly to problems with the cable installation and the way it ties to the house's electrical ground. There are inexpensive methods of fixing such ground loop problems, so I would not let the risk of a ground loop prevent you from moving to a good amp like the 7700.

Balanced interconnects are not necessary to get a good, quiet system - plenty of us have had great success getting dead-quiet setups with standard unbalanced cables. I wouldn't get rid of the Yamaha just for the sake of having the option to use balanced interconnects. On the other hand, the 990 is a great piece of gear that offers some nice features the 3300 lacks (DVI switching, Pro Logic IIx, more robust bass management, video transcoding from s-video and composite to component, a third component input).

I had the hum as well it was not a ground loop.
We have a new house and had installed some lights under the counter in the kitchen with bult in dimmers. When those dimmers were on there was a
loud hum from the 7700. When off no hum. Strange but true.

Dimmers and flourescent ballasts are also very good candidates for inducing hum. Compressors (like in your fridge) can even do it, for that matter.

I just swaped out my 7125 (two prong) for the 7700 (3-prong) and I have MASSIVE ammounts of hum. I am not talking about a little distracting but where that's all you could hear out of the speakers!!!

I was using two power conditioners to handle all of my equipment so I ran a wire between the ground lugs on both units and the hum was cut down by about 75%. I then found the source - it's the light kit on my celing fan! A few months ago I put a dimmer switch in and I am sure this is doing it as I have heard they are well know for that, do they make a special kind of a dimmer that does not introduce massive ammounts of noise?

One more thing - I am using balanced connectors.

Zofo wrote:

One more thing - I am using balanced connectors.

Without the external obvious causes of hum I had a ground loop hum (see above). Lifting the ground with a cheater as a test worked, but was not considered advisable as a solution by outlaw tech-support.

Using balanced cables, hum gone.

My hum problem is solved. I checked all the usual suspects including completly disconnecting my sat antenna but that didn't cure it so I checked the rest of the cabling and found one of the cables from the 990 to the 770 was not fully inserted in the back of my 990. Even with all the panel space on the back of the 990 those big Canare connectors and boots that Bluejeans uses make it a tight fit. When I seated it correctly there was complete silence.

I stayed up until 2:30AM last night listening to music, mostly SACDs, and thus far I am very pleased with what I've heard. Tonight a movie or three.

mike

Hi there. I've not troubleshooted it yet but wanted some suggestions. I don't have a loud hum as such, but I recently noticed that after turning off the 990/7700 combo with XLR cables that there is a high pitched whistle after turning everything off that fades out, kinda like something is 'draining' out so it goes from high to low and is gone in a second or so.

What could cause that?

It sounds to me like the amps' capacitors discharging, if I had to guess.

Hello,

I would like to add my "experience" with hum. I just received Model 990/7500 combo. And right of the bat, I was greeted by the hum. I pretty much disconnected everything and rearranged the power cables with no reduction of hum. I finally put everything back together and started all over again. During this exercise I noticed few things:
- I was able to "effect" the hum level while playing behind the rack (high, low, etc.)
- The hum was there when the RCA cable was connected between 990/7500 (attached on both ends).
- The hum was there when the RCA cable was only attached to 7500 but not to the 990.
- The hum was gone once I disconnected the RCA from 7500.
- I thought the cable was acting somewhat like an antenna.
- The hum was not there when I used my old Rotel Ampplifier (stereo) using the same cable.
- I changed the RCA cable with a Monster Cable ULT-I600, 4feet, the hum went away. Nada, zilch, zero.
- I will be bringing home some instrument tonight to see if I could measure any interference coming out of 7500 when compared to Rotel.
- Rotel is "power consumption" rated at 400 Watts vs. the mighty 1800 Watts of 7500. Though, I do not know if this should make any difference.

I will let you know if I have the right instrument (Tesla?, Gauss?, I am very poor in electromagnetics...) and the results of my measurements.

Cheers,

H2O

Thanks H2O for sharing your experiences (frustrating) with us about hum. When using 990/755 combo I had no hum even though the connections were RCAs-unbal. I did have the buzz referred to in this thread:

Other thread-buzz with voltage change due to wind turbine really cooking

I moved the 755 to a different location in the house and bought a 7700. Ran RCA's got hum. Used XLRs and no hum. Yes I went thru the drill of isolating each component out of the system as a potential source. Still haven;t figured out why, but I've solved the hum (ground loop) problem by using balanced connectors. Yes I tried a "cheater" but since Outlaw doesn't recommend it I won't "cheat".

The buzz with voltage increases from 122 to 125 volts still exists audibly, so that's a constant.
What is not a constant is that the XLR balanced cables eliminated the hum. Still dunno why.

"Input" (pun not-intended ) appreciated.
And I gotta tell you I love the 990/7700 combo.