PSW350 hum

wbz

I have a PSW350 sub less than a year old. It recently started, or I recently noticed, a hum from it. It is not from the driver but the cabinet itself. Sounds like the transformer itself is humming. Is this a known problem?

danger boy

yes and no.. the amp on the psw350 does give off a low level hum .. i have it in mine too. it's not very loud. only when you get real close to it with your ear. it does not affect how the subwoofer works..

rs159

The only Polk sub I have is the PSW202. There is a very, very slight little hum when you turn the gain up to stupidly high levels. Not a problem since your head would have to be 1 foot away all the time to hear it.

wbz

This hum is not affected by the volume or level control. It is even there with no input from my amp. It is a mechanical hum coming from the rear of the cabinet itself. Though low level, I tend to hear it between passages when the house is very quiet. It didn't hum when new. Is this a known problem?

RuSsMaN

Search the forum on 'ground loop'.

Cheers,
Russ

mantis

Ditto,
very muchs sounds like a grounding Problem.You can lift the ground from the amp.

wbz

Nope. Not a grounding problem. This is not athree prong plug and it does it with no input plugged in and the volume control does not affect it. This is definately a mechanical hum. Thanks for the tips. I was just wondering if this was a common problem. I think the next step is to open it up to find the culprit before calling Polk for warranty repair.

wlrandall

Does it disappear when the input is connected? Or is it there all the time?

wbz

It is there all of the time.

BeginnersLuck

Does the amp run abnormally hot? (Hotter than when you first got it?)

-BL

wbz

No.

BeginnersLuck

Go take the sub to a different room in the house and make sure the outlet is not on the same curcuit as your current HT setup...Could be a grounding problem...just becasue power cord in not 3 pronged does not mean you are immune to grounding issues!

And this time, actually try doing a search for 'ground loop'

Oh, and welcome to the forums!

-BL

wbz

Nice attitude BiginnersLuck. I am quite able to determine whether there is a grounding loop or not. The problem is clearly a mechanical vibration most likely from the transformer. My intention in posting was to see if this was a common problem or not.

You can get more in depth info on groud loops & troubleshooting in in rec.audio.tech, a newsgroup on the USENET.

BeginnersLuck

Originally posted by wbz
Nope. Not a grounding problem. This is not athree prong plug and it does it with no input plugged in and the volume control does not affect it. This is definately a mechanical hum. Thanks for the tips. I was just wondering if this was a common problem. I think the next step is to open it up to find the culprit before calling Polk for warranty repair.

Clearly, you are not "quite able to determine wether there is a grounding loop or not" becasue of the statement above. Ground loops can be caused by 2 pronged plugs as well as 3 pronged plugs. I am just trying to help you out the best way that I can. Obviously, there is a problem with your current setup because a low level hum is common in some amplifiers but if you can hear it from you listening position then there is a porblem. Some transformers have a tendency to hum when fed unclean power usually coming from a ground loop in the system.

So just relax and have fun, even though you might have to do it without a subwoofer while it is in for repairs, if it comes to that. Hopefully you can get your sub problem resolved soon.

Later,
-BL

wbz

Define "unclean power" and how this causes a transfromer to hum.

Any hum that would appear at the output of an audio amplifier is a defect. No good amplifier would "have a tendacy to hum".

A ground loop implies, by definition, multiple paths to ground. As stated in previous posts this "hum" occurs with no inputs connected to the amp. Therefore it can have only one path to ground. That would be the path back through the third terminal of the plug. Which there is none.

In any case. This hum is mechanical. Generally caused by faulty transformer core laminations or the surronding frame or mounting of.

If/when I get to the bottom of the imediate problem I will update the post.


later~~~
w

Tour2ma

"Unclean Power" - noise in the AC current created by motors and other AC driven devices internal, e.g., the fridge or A/C, and external, e.g., industrial compressors, your neighbors’ A/C, to your home.

Originally posted by wbz
I think the next step is to open it up to find the culprit before calling Polk for warranty repair.

While it could be something as simple as the transformer is not anchored well, opening it up is NOT a good idea warranty-wise… recommend you just take it in.

Originally posted by wbz
Any hum that would appear at the output of an audio amplifier is a defect. No good amplifier would "have a tendacy to hum".

No, all transformers hum to some degree, some more than others. However, as BL stated, it should not be that audible to you. My Carver M1.5t, which I think is a pretty good amp, always produced a hum you could hear up to one-foot from my speakers. Over time it would grow in volume and I found this was due to oxidation of the input connections. This developing lack of proper “grounding” to the pre-amp via the interconnects’ shields was responsible.

Anyway the point here is that you are confusing grounds with ground faults. Grounding is necessary at many points in an audio system. Try disconnecting the ground lead from your turntable/ phono-cartridge to your pre-amp and see what I mean.

The above said, I do agree that yours is not a grounding problem. A grounding problem would tend to manifest itself through the speaker, not the cabinet. However…

Originally posted by wbz Nice attitude BiginnersLuck. I am quite able to determine whether there is a grounding loop or not. The problem is clearly a mechanical vibration most likely from the transformer. My intention in posting was to see if this was a common problem or not.

Fair enough intention, but give credit to those trying to help you. And it was not easy as it was seldom clear what “amp” you were referring to “not having an input to.” The sub’s? Your receiver’s? Believe me when I say that the attitude on display here is not coming from BL. Seven posts in over a year, all in this thread and you lay the old “attitude” on BL because he cares enough to take a couple runs at getting something through to you of which you clearly lack an understanding? BL’s kicked in enough in his two-months here to have earned a little more respect than that.

BTW, two prongs… one is “hot”, the other is “circuit ground”. The third prong? Also a ground, but for the cabinet, etc. so the consumer is not lit up should a short develop in the device. Stuff learned because I read comments back on a misstatement I made in this forum. I read, checked it out with my VOM, and what do you know I was wrong, commenter was right and I learned something. Comes from allowing for the possibility that I don’t know it all… as much as I’d like to think I do. Try it sometime.

wbz

okaaayyyy.

No, nobody knows it all but if you knew my credentials you might agree that I stand a fair chance of diagnosing problems with audio amplifiers, loudspeakers, power systems, & proper system grounding.

w

Tour2ma

wbz,

A restrained, reasonable response to a half helpful, half antagonistic post written at 04:00. Not that it should necessarily mean anything to you, but I respect that.

I'll take your word that you have expertice in electronics. Why have you chosen not to lend it to others in the Club? Folks often post questions in this and the Electronics areas that beg expert advice.

BeginnersLuck

And if you knew our credentials, you might agree that we all stand an equal chance, as some members may be more specialized in certain areas than others...Thus the whole proscess of learning! Isn't is great?

-BL

wickman

the low level hum you are talking about is a problem in a majority of psw350's that was talked about well over a year ago...it doesnt affect performance though...i remember someone posted a fix quite a while ago but i do not know if worked and do not even remember what it was...you can try a search but this topic goes back before they redid the forums,so you may not be able to find it...