Axiom Home Page Forums General Discussion Technical Questions Anoying humm in my LFR1100

I refused to believe that Axiom would send out new
speakers or components with a defect. So for the past 2 months I have been listening to my LFR1100 with a definate humm coming from the mid and woofers.

I have tried replacing my RCA interconnect cables just to make sure it was not them.

I have tried a different amp and pre-amp setup

If I unhook the LFR DSP from the amp, the speakers are dead quiet. If I hook just the front speakers up, and go directly from the pre to the amp and bypass the DSP all together, they are dead silent.

it sounds like a ground feedback loop humm.

is there any thing else to try before rattling the doors at Axiom to get a new DSP sent out to me as the one they sent seems to be DOA?

Sounds like nothing is defective and that the real problem is a ground loop in which you will have to solve methodically yourself.

If the plug is a 3 prong try lifting the ground. I use a modified 2 prong extension cord . Ground loop hum can be a real sob. My phono preamp picks up all kinds of stray EMI . Try moving the dsp as far away from everything else as you can as a test.

Do you have Cable TV/Internet connected to that system?

If so, that is a good place to start as troubleshooting found that was the culprit. My EP800s hummed as did my previous Velos. It was easily fixed on the 800s by unscrewing the Chassis Ground screw. With the Velos it was much more complicated...

TAM

Matt, if I followed, the LFR DSP appears to be the only factor causing the hum. All your changes, including a different amp and pre-amp, didn't affect the hum problem as long as the LFR DSP was still in the circuit.

There isn't any apparent way that simply inserting an additional component(e.g., the DSP)in the middle of a circuit could create a ground loop which previously wasn't there. Therefore it seems that the problem is likely to be internal to the DSP, which would need repair or replacement.

A few more questions that might help to herd the problem into a corner...

- Is the DSP plugged into the same circuit as the other equipment ? Just checking on this one...

I wanted to ask "how about switching off or unplugging the DSP and waiting for the P/S to bleed down" but a bit worried about spikes/noise going out to the amp & speakers so maybe skip that.

- Do you still get the hum if DSP is connected to amp inputs but preamp is not connected to DSP ?

- Is the hum on both L & R channels ? On both front and rear channels ?

The hum is there when the DSP is connected to the Amp. It does not matter if it is turned on or off. Even unplugged with not power cord attached to the back of the unit, and completely disconnected from the pre-amp. I still get the humm.

I did not budget nor do I have very long RCA cable to try and put the DSP on the other side of the room from the rest of the equipment. It was never discussed with my by Brent when I inquired about the unit that it would humm if connected.

I get the distinct feeling that there must be some form of short inside the DSP that causes this buzzing humm on the speakers.

OK, that's very clear. And very weird.

The part I really don't get is that it hums both with and without the power cord. It's easy to come up with explanations for one or the other but not both.

I would call Axiom. It's always possible that something was jarred during shipping!

spoke with Brent and I am shipping back the DSP for them to take a closer look at. It is really weird. But I am not worrying as Axiom is top notch on their support side of things and I am sure that they will figure out what is going wrong.

They have no control over how the unit gets handled when UPS gets it. So it might have been something getting whacked out of spec in shipping from some nob dropkicking the box to the other end of the shipping dock so he doesn't need to walk the extra 18 feet. ?? who knows.

I drop kick test all my parcels prior to shipping. Like you say, you don't know what some whiny baby is going to do to your parcel. Best to let the guy that built it figure it out, since you have done all you can on your end.


I will share a little story with you. I bought a high end Phono preamp (1g) and it hummed like a mofo, I hooked it to my Yamaha, my Denon and my 35yr old pioneer and it still hummed like a mofo. 3 different systems entirely, I sent it back and they said it was perfect, dead quiet and it was reputable brand. I bought a different brand and it hums too, though not to the same degree mind you ,go figure. I wrote most of it off to old house wiring syndrome. Also there is so much damn electronic interference in a house these days , god knows what is doing it.I managed to reduce it down to a manageable amount using a few tricks here and there.

Keep us posted, always good to know how things work out.

Hi Matt,

Can you describe exactly what your system consists of and how you have it hooked up to the LFRs/DSP? From what you are saying it sounds as if there is a ground loop issue in the connection of the DSP to your amplifier(s). The DSP box itself is earthed, but the signal ground is floating, so it in and of itself can not cause a ground loop. However, because all 4 outputs share a common ground, there could be a grounding issue if you are using more than one amplifier to power your pair of LFRs. In that case the loop exists between the two separate amplifiers.

Thanks,

Andrew

I have an Anthem MCA5, so there are 5 channels inside the one unit.

I have tried 3 different pairs of RCA cables just to make sure that it isn't the cable itself that is causing the humm.

The LFR1100 speakers are connected to the front and surround amps on the back of the MCA5. (plugs 1,2,4 & 5) The remaining plug 3 is the marked as the center channel amp.

If I have just the LFR1100 speakers hooked up to the amp, and turn it on, it sounds fine. (No real decernable humm).

As soon as I run an RCA cable from the DSP (left or right out) to the input for those respective channels on the MCA5, there is a noticeable humm that you can clearly hear from 5-6 feet away. The DSP does not even need a power cable pluged into it, nor does it need to have power, or turned on for this to happen. Just the simple fact of having the DSP outputs plugged into the amp. You don't even need the pre-out even plugged in. So I have concluded that the fault must be inside the DSP.

I will admit that most of my latter testing was exclusively with the left channel, but I had noticed it with the right before I started doing cable swapping.

I have not tested it with the XLR type cables as I was told by Brent that it should work best to stick with one type of cable or the other, and my pre-out doesn't do XLR. (the amp and the DSP does have that option).

As per Brents instructions, I have packed it back in the box and was waiting for a return lable, but I can pull it back out if you want me to test more.

I can ask my neightbour around the corner if he has some spare XLR to XLR cables hanging around to test with if that would help?

Sometimes my cat thinks there's an annoying hum coming from me when I'm busy doing something.

We have made a move forward. I managed to have a chat with Andrew, that led to another chat with Sonic Frontiers who makes made my amp. The conclusion was that I was using RCA cables and the DSP's floating ground that makes it more compatible with most amps, made it not so friendly with mine.

So the going conclusion was that when I asked here if I should go with XLR vs RCA cables, the correct answer for me was XLR. I borrowed a neighbours pair, and you can hook them up with ZERO noise from the amp and speakers with the DSP turned off and plugged in. Where before I got a pretty loud hum.

But as soon as you turn on the DSP, I have gone from a humm now to a hiss. New sound.

That does not seem like an acceptable resolution. Can one of the 2 companies modify their respective product.

Is the hiss still with no content playing or components connected/powered?

the hiss is with no content playing. its no longer that 120hz humm so it's kind of like the sound you get at the beginning of a record where there was no sound playing but you heard something. hard to explain.

Is the volume turned down/off?

It sounds like you need to call Axiom support again. Perhaps there is a problem with the DSP after all!

Maple.. that's like Canada's Wonderland area. A heck of a shorter distance than going up to Dwight.

I am wondering as I know that you have LFR1100's if it would be possible if I could arrange some time to visit with DSP and an Amp in toe and give it some tests against a known working unit? They are pretty sure that the issue is not inside the speakers, and they are the Q-B to move around. But an Amp and DSP will easily fit in the back seat and love to go for a drive.

The last time that I spoke with Axiom it looked like I would be taking a drive up there with my amp and DSP and leaving it with them for a week or so.

I am thinking now that you are quite a bit closer and if your equipment doesn't do what mine does, then there is little argument that can be had when I say HEY.. its been tested and ...

Hi Matt,

Yes, I'm certainly closer than Dwight but actually a bit further than Wonderland. I'm almost in Richmond Hill -- the wrong side of Maple for you!

Anyway, yes, I'd be happy to have you come over and bring your DSP and amp. When would you like to do this? Evening or weekend?

I am sure if there were any hum in my LFRs I'd have heard it by now but our first step will be to have you listen to my existing system to confirm this. You may want to bring a CD, DVD, or Bluray that is familiar to you. Is your current hum/hiss constant or does it vary depending on source material?

We may want to get some direction from Axiom but I'm guessing the first thing to try would be switching your DSP with mine. If that doesn't result in any unexpected hiss or hum I would think it essentially rules out your DSP as being the cause of the problem.

Cheers!

Mike