Axiom Home Page Forums General Discussion Home Theater Subwoofer hum

How loud is the dreaded hum ? And at what volume does it usually show up? I just got my Hsu VTF 2.3 today and it sounds fantastic, but... I fooled around with the volume knob and noticed it begins to hum noticeably at 1:00 and beyond. It is not real loud, but when all else is off and quiet it is audible. Is this the ground loop problem? I do not have the cable coax going into the receiver. Maybe a noisy AC line? Maybe defective sub? The sub just by itself makes some hum but much lower in volume -- with the line in connected it is louder but not audible until 1:00 on the dial.
Any thoughts here would be appreciated?
Thanks
MArk

Not familier with that sub but the Axiom EP500/600 have a ground screw on them to help with hum.

I think I read a post by Alan Loft that if the sub hums with no line connected, there might be something wrong with the amp in the sub.

http://www.axiomaudio.com/boards/ubbthreads.php?ubb=showflat&Number=187452#Post187452

No ground screw on the Hsu. Could be a ground loop but it sounds like you have the gain way to high? Have you calibrated the Hsu with the rest of the system? Most Hsu owners find somewhere around 9 to 10 o’clock is about the highest the amp should be.

Mark, as the others have indicated, if the hum occurs without being connected to other equipment, a ground loop can't develop. If it's a faint hum it may simply be that the noise level of the sub amp is audible at that high of a setting but wouldn't be audible in normal use. If it's louder than that it might indicate a defective sub amp.

You are exactly right, the best setting for me is around 10 and there is no audible hum either connected to the recevier or not. I only noticed the hum when it is turned way up -- and not in use since that would knock some walls down...But the hum is a little louder when connected to receiver (again only at the higher amp levels (>2 clock)

I guess I was curious to know if the humming at high amp levels is normal?
BTW - the hsuforum does not cover much of this stuff which is why I am relying on you guys -- thanks for being patient with me.

No they don't see as much traffic @ the Hsu forum as they do here. The people here are a lot nicer too

That's why I keep coming back

In my experience with subs, humming at high amp levels is "normal". I don't know why amplifier manufacturers have such a difficult time rejecting power line noise.

I don't find that to be the case. Sounds like you might need a line conditioner Tex.

I emailed Hsu support yesterady and explained my situation. They responded to say that the hum at high gain levels is normal. It was attributed to the tremendous gain that the amps have. He recommended that I use the 9 o'clock position for the sub volume -- which works fine as there is no hum at all at this setting -- and it sounds fantastic.

FWIW -- It just seems weird that they would design a piece of equipment not to be used for 2/3 of the volume range. If you can't really use the full range then why have the knob able to access it. It would be like having a speedometer that goes to 300mph when most cars can only go 130 mph max.

The power useage is not so much determined by the amp but the signal the amp in given. They have to have a wide range on the gain because of the different signal levels of different sub (pre) outs.

Ok.I think I understand. So the signals coming from the pre-out are not fixed. That would explain it. I was thinking that there would be a standard output level, eg. +/- 5 miilivolt. My background is in chemical engineering so this signal processing stuff is not my bag

Pretty much. Not only from the sub pre outs but from the speaker level inputs and regular pre outs from stereo pre amps.

A line conditioner would most likely solve the problem. But 60Hz noise should never enter the amplifier circuits. It's a result of poor filtering and/or lay-out and/or too few layers on the printed circuit boards.

Try turning down your sub volume -5 db and see what happens...see if the humming is related to the volume setting on the receiver...

Any recommendations here? I have seen that APC sells one but it looked to be $300. But this had more than I need. Do they sell just line filters that can be plugged in or are they hard-wired?

When the sub volume is lower, the receiver does add some hum but only at extremely high levels of volume nearly 0 dB on my HK.

This amount of hum is way less than when I crank up the sub volume at normal receiver volume.

I think there it is either AC noise that is passed through or some noise creeping in from the receiver through the rca cable connectors. I need to get an AC filter and Maybe I'll buy the Axiom or Hsu sub cable? But the Monster cable I use now should work fine. it doesn't seem to be interference because I have pulled the receiver out (temporarilly) and moved the sub cable all by itself with 2 feet of space between it and anything else. That did not help at all.

Mark, yes there's a recommendation: since you've reported no hum at a more normal setting on the sub level control and that it sounds "fantastic", there's no need to do anything, including spending money on any expensive magic power conditioning items.

Exactly. Hammer, SVS even notes that receivers give out sub line-out distortion at higher levels and recommends to set the sub volume at -5 in the receiver, then calibrate for that.

So, I'd pass that recommendation to you, set the "woofer" level to -5 and that will reduce the distortion hum you are getting.

Good idea. And that is just what I'll do...

So if I understand correctly-- you don't recommend going to Mapleshaderecords.com?

BTW-- I like you sig.

Well, I do recommend going to Mapleshade for entertainment. It's been brought up here a few times over the past 3-4 years and the absurdity of their descriptions has always been good for a few laughs.

I agree with John, don't waste your time with those snake oil tactics.

Happy Holidays!
I was just kidding about Mapleshade -- mostly because of the recent posting that attracted a lot of attention.

Since the system is ok at the current volumes I don't need to do anything. I might look into some AC filters but they are a lot of money and I am not sure that is an issue -- again since I can't hear hum at normal volumes. What is puzzling me is that it gets a little worse when the AVR is connected.
Enjoy the holidays!

Have you tried a different AVR, maybe you could borrow one from a friend?

Do you have the AVR and the sub on the same circuit?

No I haven't, but that is a good idea.
Now I just need to make some friends...

Yes, the AVR and the sub are on the same circuit. Will this help the potential ground loop issue?

Merry Christmas Boar Members!!!

Yes, having all of your audio/ video on the same AC circuit will help eliminate ground loop problems.

Good to hear from you again, Bernard, and a Merry Christmas to you too.

I didn't eat THAT much over the Holidays................... (yet!)