Hi all,
I recently purchased a gently used 7500 in my gradual process of moving from a receiver to separates. I have a pre/pro on order, but probably won't get it for a while, so I'm using my old Yamaha RX-V1 receiver as a preamp in the meantime. It has only unbalanced outputs, so that's what I'm using into the 7500. I currently have the buzzing/hum that so many others report, and have combed this and other forums for troubleshooting tips, some of which worked better than others. By the way, for others looking to try things to reduce or eliminate hum, check to see if you're using compact fluorescent bulbs in any of your light fixtures. My buzzing was dramatically reduced when I removed those bulbs from a ceiling light fixture and replaced them with incandescents -- and the fixture was in another room on another circuit!

Anyway, back to my issue. In one place on the hundreds of forum pages I've read I saw someone suggest that the unused amplifiers in a receiver being used as a pre/pro might be causing some of the hum, and I wondered what the Outlaws thought about that. Could this be contributing to my hum problem? I'd love for that to be it, since I'll eventually have a dedicated pre/pro with balanced outputs.

I'm also curious about popping noises coming through my speakers that were never there before. Some come when I power up, even if the 7500 is the last thing turned on. But the most noticeable (and annoying) is the pop I hear in my right surround speaker every time my preamp (receiver) switches from Dolby Digital to some other audio mode, or when switching inputs. This is almost unbearable when a DVD is loading, because of all the menus/previews/etc that jump around in audio modes. They're not random pops; I can predict when they'll happen and they never "disappoint" me if you know what I mean. Any help on what this might be coming from would be much appreciated. By the way, the 7500 is the only new piece in my system at the moment, which is a relevant point to make.

Many thanks,
-Brad

When you talk about humming, is it coming from your speakers or are you talking about "mechanical" noise coming from the transformers on the 7500?

Also, sounds like the popping noise is junk that the receiver is sending to the amp through the preamp outs. That should go away depending on what prepro you go with. When I had a 990 it would do a popping noise everytime I switched audio modes.

It's a bit of both for me, actually. I can hear a hum from the amp itself, which appears to be...well..."amplified" in my speakers. It's sometimes louder in one speaker and sometimes about the same level in all speakers. Once I solved the fluorescent bulb thing, it went down to a level I can ignore during music or movies, but it gives me a metaphorical and sometimes physical headache knowing it's there. During my troubleshooting, I noticed that the only time I don't hear the buzzing from the amp and speakers is when NONE of my other electronics on that circuit are plugged in (including the receiver) and the amp is plugged into my Panamax power conditioner. Plugged into the wall, I hear the hum. Plugged into an outlet on a different circuit, I hear the hum. Plugged back into the Panamax, hum goes away (makes me feel a bit better about dropping that money for the conditioner). But of course the very next thing to plug back in is the receiver, and the hum comes back, whether the receiver is plugged into the wall or the Panamax (although I haven't tried the amp and receiver on separate circuits).

My thoughts as well, but I was on a roll so I threw that question in there too. I'm hopeful that the pre/pro (Onkyo PR-SC885) won't exhibit these issues, but I probably won't get my hands on that until January.

Thanks for the feedback.
-Brad

I know that the 7x00 series of Outlaw amps are very finicky as far as power coming from the wall goes. I'd say that these amps pretty much require a dedicated circuit with nothing else on it.

Problem for you is to get an amp that isn't as particular about the quality of AC fed to it AND has same or similar power rating can be quite a bit more expensive. I'm assuming that you got a good deal for the used 7500.

I'd suggest using balanced interconnects to go from the new Onkyo prepro to the 7500 once you get the prepro. That should take care of most if not all of the noise being fed into the speakers.

As for the humming of the transformers, if your domicile has noisy power to begin with, even a dedicated circuit won't totally get rid of the hum, even if the amp is behind a power conditioner, so you have to figure out how much hum you can live with.

Either that or get a different amp.

Yes, and it would almost certainly be more cost effective to have the dedicated circuit put in rather than sell the Outlaw and pick up a less finicky amp of equal or greater power.

Balanced interconnects are just waiting for the pre/pro. If that eliminates the buzz in the speakers, I can live with the hum in the amp itself. Thanks again for the info.

There's a 3 part blog entry on the Klipsch forum about hum and buzz. I think you have a combination of ground loop and poor AC quality, that's just my guess.

http://forums.klipsch.com/blogs/andyw/archive/2007/11/09/hum-and-buzz-part-i.aspx

A couple people have suggested that the AC quality coming into my house is poor, and I thank them for their opinions and comments. Is this something my utility provider can do anything about? The house is about 35 years old, and the electrical service is buried (no electrical or telephone poles in the neighborhood). If I call the power company, what do I ask them to do?

Thanks again,
-Brad

For those who appreciate a sense of closure in their forum Q&A, here's a follow-up to my previous posts. I got my new pre/pro (Onkyo 885) and hooked it up via XLR cables to the 7500. Almost all of the noise in my speakers is now gone. The 7500 itself still makes some mechanical noise, and a little of that is transferred to the center channel speaker (the speaker closest to the amp, but this could be a coincidence), but entirely liveable. If I had more time, it would be interesting to see if the buzzing was still there if I used unbalanced connections between the Onkyo and the 7500. If not, it would strongly suggest that the unused amps in the receiver I had been using as a preamp were the culprit, which was actually my initial question in my original post. I suspect it was a combination of the Yamaha and the unbalanced connections, but now that I've got it the way I want it, I don't need to fix what ain't broken.

Now I can actually relax and enjoy the wonderful sounds coming from the 7500 and 885. I'm also thinking about trying out one of those PS Audio Humbusters to get rid of that transformer noise. There seems to be mixed reviews on its effectiveness, but I'm interested in giving it a shot. If I do and it works, I'll post back here later.

You might want to ask the Outlaws to send you out one as they did for me.

Will be interested to hear the results of that.

Glad to hear that moving to the new prepro solved most of your noise issues though.

Thanks for the suggestion. I have submitted a "support ticket" with Outlaw now, humbly requesting one of these devices to test this theory. I am truly at their mercy with this, because I found out yesterday that PS Audio no longer manufactures or markets the Humbuster, and the new product they're pushing (called a Noise Harvester) does not remove DC from an AC line.

Worst case scenario... if the problem is with the amp, the 7500 is still under warranty, and I kept the double boxing.

I'll post it here if I find out something new.