AVS Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·

Hi.

 

First time poster newbie here seeking help.  I recently purchased a Klipsch SW-110 sub to complete my 2.1 setup and have been introduced to the infamous and annoying subwoofer hum ever since connecting the first set of bare speaker wire on the right channel from my stereo amp to the sub.

 

My setup:

                                                                           /--> bookshelf speakers

Laptop --> external USB DAC --> AudioSource AMP-100 

                                                                           \--> subwoofer

 

I'm using both of the amp's Speaker A + B terminals at the same time, to respectively connect the speakers + sub via bare speaker wire.  Only the sub produces the constant hum.  While it's not loud, it's certainly audible, especially since it's under my computer desk and I'm typically adjacent to it for hours.  

 

Initially I thought it was ground loop, but both the sub and amp power cables are 2-pronged and connected to the same power strip.  My cable service was cut off last year and there's no coaxial cable nearby anyway, so no TV issues to worry about.  

 

Interestingly, if I connect the amp to the sub via RCA cables (either the red or white end or both -- any combo really) the hum ceases.  That's even with the speaker wires remain connected to the sub and RCA cable(s) at the same time (which I know is not advisable, but it was for testing purposes).  I read that speaker wire aren't shielded like RCA cable, so it's more susceptible to EMI / RF, but I was hoping for a solution that doesn't involve buying expensive equipment (this also makes me wonder how people handled this in the days before AVRs).  Then why not stick with RCA and ditch speaker wire?  Because that results in two problems:

 

1) The sub's volume can't be controlled by the amp because of its low level (fixed) signals.  I want to be able to adjust speaker and sub volume simultaneously.

2) The full signals going into the sub is overpowering to the point that it doesn't sound comfortable unless the sub's gain is around the '1' setting.  I read that someone added a passive preamp (aka stepped attenuator) between the AudioSource AMP-100 and their sub to handle this issue, but I don't know if that allows volume adjustment on both speaker & sub.

 

Thanks
 

·
Banned
Joined
·
15,491 Posts
You've already found the cure. Controlling the amp and sub volume simultaneously is accomplished at the source. But another problem is that you don't have any method of filtering the lows out of the main amp.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #3 ·

Indeed, I was aware of the disadvantages of no bass management from a stereo amp and the overlapping bass frequencies before purchasing all the equipment.  I can cope with that.  

 

Regarding the source - unfortunately, my DAC doesn't have volume control and I prefer not to do so at the digital domain (i.e. from the computer) because it would reduce resolution.  I also prefer a physical volume controller.  Would an attenuator between amp and sub work in what I'm trying to accomplish?

 

Thanks.
 

·
Registered
Joined
·
90 Posts
I have the exact setup as yours connection wise, except it's not humming
And there's an ungodly amount of mains cable, signal cable, all sorts of cable down there with my speaker wire
Don't really know what may be causing your problem.


As you already pointed out, the line out of the AudioSource doesn't change volume. Putting an attenuator between the amp and sub would allow you to change volume for the sub... independently of the mains volume, which is not what you want.


What you need is basically something that takes the signal from your DAC and splits it out to the amp and the sub along with a volume control. What that mystery device is, I don't know. I have tried using a Y-splitter and it did not work well (signal distorted on the speaker amp) but it might work for you, it depends on the particular DAC output, amp and sub input circuits in question. Ideally you want an active box that takes one pair of input channels and gives two pairs of output channels. But I suspect that for the price of such a beast (or any device that could be cudgeled into such a role), you could probably buy a whole new amp with a proper sub out...
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #5 ·

Nice to know you have the same wiring setup without the hum.

 

When I move my speaker wire (lift them up a bit) there's no change to the hum.  The only time it varies is when I change the sub's gain (e.g. if it's near 0 then it becomes inaudible).  My laptop is connected to an external monitor via HDMI cable and I think the speaker wire touches it.  Could that be it?  In my research I read that HDMI can affect this problem.  I haven't lugged the sub and amp into another room or location yet because that would be a bit of a pain, but someday I will to try to isolate any potential source causing the hum.

 

I found an older thread and from  Kilian.ca's post , (s)he had the same problem and found a unique workaround by connecting his/her sub to a soundbar's sub out, in addition to speaker wire from sub to pre-amp.  However, I'm not sure whether the problems remains regarding the sending of the full signals to the sub and not being able to control the volume.  Maybe that mystery device is a pre-amp?  Aren't those expensive too?
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #6 ·

Quote:
Originally Posted by Joe0Bloggs  /t/1468507/sub-hum-when-connected-to-stereo-amp-via-speaker-wire#post_23210130

As you already pointed out, the line out of the AudioSource doesn't change volume. Putting an attenuator between the amp and sub would allow you to change volume for the sub... independently of the mains volume, which is not what you want.
I take it that means the amp won't be able to change the sub's volume with the attenuator in between because I presume the attenuator only inputs and outputs using RCA cables?  Like this?: 

Sources, etc. --> Amp --> Attenuator --> Sub

                              \--> Speakers

 

 

Update: Success!

It's not the HDMI cable.  After more testing I found a workaround based on Kilian.ca's method, but without the need for an extra device like a soundbar.  It's even free:

 

1. Connect the white & red RCA cable terminals to the sub's input jacks.

2. Connect either the white or red terminal (only one of them, not both) of the same RCA cable on its other end to one of AMP 100's Input Line 1 jacks (it oddly doesn't matter if it's the red or white jack). For clarity sake, the input Line 2 is still used for the DAC's RCA cables because that's the amp's main input.

3. Place the remaining white or red terminal of the RCA cable so that it makes direct contact on top of the remaining Line 1 jack.  Voila!

4. To ensure that RCA terminal stays in place simply tape it next to the amp and semi-wrap around it.

 

While it doesn't completely remove the hum (100%) or is as silent as connecting the RCA cable into the amp's output jacks (98%), I'd rate it as a 85% eliminated.  Now it's much more tolerable as the hum sounds like it's part of the ambient noise with all the usual electronic background noise.  I like to think myself as possessing excellent hearing, so I imagine the average person won't even notice.

 

I'm sure electrical experts can explain this.  If both terminals are connected into the amp's jacks (rather than one of them), hum is also reduced, but only by 40%.  Anyway, I also hope this is safe because the idea behind this is simply trying to leverage the existing tools I have: amp's input to sub's input jacks. No outputs are involved, so theoretically signals aren't being transmitted between each device?
 
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top