Axiom Home Page Forums General Discussion Stereo LFR1100 Actives hum

I don't remember who first mentioned the significant hum coming from their LFR1100 Actives, but that's been the case for me as well. It doesn't help that I don't have all of my equipment on the same circuit, and there's no easy way to remedy that. I read at one point it can help to have all relevant circuit breakers on the same side of the electrical panel, and I don't even have that. I still need to run an experiment at some point in which I run extension cords to some equipment so they're all at least on the same side to see if it actually makes a difference.

In the meantime, I heard someone had luck eliminating their hum with this product:

Emotiva CMX-2 Precision Common Mode AC Line Filter With DC Offset Eliminator

Seemed worth a shot for an easy solution. It arrived today, and I think I shot myself in the foot. I tried it in various configurations. Since it's just two outlets, first I did both DSPs, then both amps, then just the amp and DSP on one side. Each one made the hum worse. As one last test, I connected it upstream and plugged the AV receiver into it. Same thing. The already significant hum was significantly worse. Deciding it wasn't going to be my miracle, I took it out of the chain completely and reverted to the way I had it. Aaaand the hum has remained at the higher volume. Whereas before the hum could be drowned out with content playing, now I'm hearing it even when I'm playing stuff. Can't live like this!

I emailed Axiom for ideas, but I figured I'd post here as well to see if any of you have suggestions.

CV, by chance do you have an amplifier in line for cable tv?
That was the culprit in my case. When the cable tech installed it he didn’t bother grounding it.
Once I had hooked up a grounding wire to the earth ground my hum was gone! Dead quiet.
What a relief.
Jeff

I have cable internet, but not cable TV. And the hum is new with the Actives. Oh, I did have some hum before, which went away after fiddling with the grounding screws on the EP800s, but after that I had no noticeable hum until I got the Actives.

Charles, if you unplug at the DSP the amp to DSP cable, is the buzz eliminated or reduced? Leave the other end of the cable connected to the amp.

Yes, the hum goes way down when disconnecting those.

And if you have all connected up normally and power everything on, but then turn just the DSP off, the hum is still there, correct?

Yes, that's correct.

So just think about that, Charles. Draw yourself a picture either on paper or in your mind's eye:

1. Amp to DSP cable disconnected at the DSP only = (less or) no hum

2. Amp to DSP cable connected at the DSP and amp but DSP off = hum

What component (amp or DSP) therefore is the conduit of the hum? What is the source of the hum?

I'll admit it's tricky. Even for electrical engineers.

I would say the amp. For clarity's sake, AVR, since that's what I've been assuming with the tests. While I think something has happened to it with the introduction of the line filter, the original increase in hum came with the Actives, which is what makes it hard for me to work out. What would you say made that hum at that point versus the gear I already had with the passive LFRs? Going with what I have now, by process of elimination the AVR certainly seems to be the big culprit. If I have all of the gear on with a source active (as in on, not necessarily playing content), the hum is loud through all connected speakers. If I turn just the AVR off, the hum is way quieter, though still there.

While I plan to replace my AVR, I'm not quite there, and I don't want to buy something new only to have the same behavior with the potential of it worsening.

Isn't it strange, that with your AVR and DSP off, and the ADA to DSP cable connected, the hum is still there? But when you remove the ADA to DSP cable, the hum subsides.

I have a theory and the explanation is technical but I will try to explain as simple as possible. This is just a theory which has not been tested. There is a 60Hz noise source in the ADA. It is between a signal input line and ground. In technical jargon, this is called a common mode noise source. The source of this noise within the ADA is not known but it is parasitic and it is related to the 60Hz power fed into the ADA.

Why do I suspect this? When you disconnect the ADA to DSP cable at the DSP, the only thing "across" the cable circuit is the capacitance of the ADA to DSP cable. This capacitance is tiny - on the order of 150pF. This small capacitance cannot pass the 60Hz current from the noise source or passes very, very little. Therefore the voltage across the cable capacitance is tiny. This voltage is right across the ADA signal input. Therefore you hear very little buzz if any at all. I don't hear anything BTW when this cable is disconnected.

When the cable is connected to the DSP, the DSP has a finite output impedance. That impedance is right across the cable capacitance. It allows 60Hz current from the noise source to pass. Hence, you hear the buzz.

The theory therefore is a parasitic, common mode noise source in the ADA that arises from the ADA's input power and is somehow impressed on one or both of the ADA's input signal lines.

If this theory is proven true, there is nothing you personally can do about it.

Oh, this is why I thought I should clarify. When you first said amp to DSP cable, singular, I assumed that meant the cable from the AVR to the DSP, since there are five cables connecting DSP to ADA. Let me try that out as well, disconnecting at the DSP all of those cables, and I'll report back.

Yes, unplugging all of the DSP to ADA cables at the DSP gets rid of the hum completely.

You could unplug just one and the hum for that channel disappears. My theory stands.

Is there something in the design that could solve this issue?

I just know that the hum I was getting before introducing the line filter was significant, but I could live with it, while this new level of hum is going to take away all of my home theater joy until I get it resolved.

I really have no idea why the addition of Emotiva's filter created more hum. Did it further exacerbate the problem through some type of interaction with the ADA?

If my theory is proven true, there is definitely something in the design causing the issue and therefore when that design is improved, the issue will go away. Not a good answer I know but the first step is to investigate the theory.

CV are you using balanced cables?

Yes and no. I'm not getting the benefit of balanced connections since my AVR only has RCA connections. That's one reason I want a pre-pro. I do have the DSPs and ADAs connected via XLR.

I'm not sure. The first things I connected to the line filter were the DSPs, and the louder hum was evident with that first step. Next I tried the ADAs, then the AVR. Ever since the first connection to the DSPs, the hum was louder and hasn't gone down since. I think something happened, but it's not like I heard anything or saw anything disturbing when hooking it up. The only evidence I have that something happened is the louder hum.

Charles, I would try connecting the same channel's DSP and ADA to the filter. That way, they will both be supplied from the same potential voltage.

How is the sub connected? To dsp or AVR? By xlr or rca?

That was one of the configurations I tried. Same result.

Subs are connected to the AVR by RCA. All RCA connections are converted to XLR before going into any Axiom gear with adapters just because I'm paranoid about RCA connections being ripped off by too-tight connectors on the ends of cables. It happened a couple of times way back in the day, but I'm still traumatized. Ha ha.

Cv, try disconnecting the sub and the internet from the avr. I assume all the other inputs to the avr are off the same wall socket As the avr ... if not disconnect those as well

rrlev, great instinct. I had already tried disconnecting the ethernet cable from the AVR with no change, but I hadn't tried the subwoofers. Pulling out Sub 1, the hum disappeared almost entirely. Plugging it back in, it was back in full force. Sub 2 pulled, no change. I had re-checked the ground screw on Sub 2 yesterday, but I hadn't yet re-checked the one on Sub 1, since it's more of a pain to pull away from the wall to have access to the back. After I un-screwed it a little more and plugged it back in, I'm treated to the same silence. Whew.

Mojo, I'm so sorry I put you through the mental exercise. I appreciate you putting so much thought into the troubleshooting. But I still have no idea why the hum got worse after introducing the line filter. It wasn't a subtle difference. The only thing I can think is that maybe the power cord of the power strip I was plugging the line filter into bumped the ground screw on the back of the EP800 just enough to make that difference. That's the most plausible thing I can think of.

Replacing an EP800 at around the same time as the upgrade to Actives made me assume the new hum was an Actives thing, especially after reading someone else was having a similar experience with the Actives.

I'd better go enjoy my system before I mess it up again.

Charles, are you using ADA-1500s or ADA-1250s?

1500s.

Rich, that was very good find. I am glad you are noise-free, Charles. Anyone using separate amps for each speaker, and particularly 1250s or 1500s, is in better shape than me for sure. The 1250 and 1500 has better noise rejection than the 1000.

P.S. Charles, that mental exercise was conducted when I first got my actives so no harm done.

Glad everything's good

I apologize for not responding sooner Charles.

I’m the individual who had luck with that specific line filter. In my case I was getting noise injected directly into my ADA1250-5s. No inputs plugged into them, just connected to the speakers.

It would appear that I have crappy wiring in my home and am getting DC noise injected across all electrical circuits, regardless of whether they are dedicated or not. The DC offset did the trick.

Daisy chaining two together actually ended up working best in my environment.

Hope that gives you more context and happy to answer any additional questions.

Hey, no worries. I'm glad we both found our solutions. Once in a while I still have weird sounds (not the hum) coming from my speakers. The next time it shows up, I'll have to remember to record it. It's just once in a while, so it hasn't seemed like a priority.

I have the same issue with my EP500 my triggers cause my hum. Once I pull the trigger plug out hum is gone.
I removed the ground screws but it is still there any ideas??Hum is in all speakers/

RJ

RJ, try to make sure the trigger cables are not running parallel and close to power cables. That's one way for noise to get in. Cables made with twisted wires may help.

Twisted cables reduce noise. So should I be separating my cables and twisting them?

I quick internet search comes up with many plausible and wordy explainations about electromagnetic fields and balancing when twisted.

I doubt many folks would need to do this. Maybe only if you where having noise issues.

Kinda cool though that that would work.

Twisted cable is the real deal. It's not snake oil. Of course if the environment is electro-magnetically benign or the equipment is immune, then you don't need it.

Sound more like ground loop problem rather than an injected signal one.

It usually is in audio. I wish someone would outlaw three prong plugs.

I have the hum with my LFR1100As and ADA1500s. When I turn on the overhead floods in cans, I get the subwoofers humming as well.

A ground loop is in the audio. The ground reference of one side is moving relative to the other ... one side is putting out zero volts relative to its ground and the other sees a signal because it’s ground is waving around relative to that zero volt output ... but you knew that ...

Its great to be an electrician.

Hire one today!

Is that from your family album Trevor?

I’d have to say he took it from mine as I literally did EXACTLY that as a 4 or 5 year old and ended up on the other side of the passage post contact.

Lol!

I was securing the wallplate screw..... zzzzzzap

Think we all learned that particular lesson at some point. Good thing we were less “grounded” back then.

lol thats funny