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Help wanted. My NHT M00-S00s are whistlingI

OK, boys and girls; time to put your thinking caps on and help me solve a problem w my powered speaker/PC set up, although I'm pretty sure its in the speakers. I just bought a used pair of NHT M-00s (powered monitors), NHT S-00 powered sub and PVC passive volume control. They are hooked up as follows- USB digital output from my Music Vault server using Windows Media player to Keces DAC. Analog out via RCAs to PVC controller. RCAs out of PVC to RCA full range input on S-00 powered sub. Only output on sub is 1/4" phono jacks to phono jack input on M-00 monitors. Sounds great, but what's that very high pitch whine or whistle coming from the monitors? Hmmm, it's there, regardless of whether there is anything playing on Media Player or not. Volume and pitch of whine/whistle does not vary w PVC volume control position. Just under the upper limit of audibility to me. Try re=plugging all cables to no effect. Try changing AC outlets to no effect. Shut off wireless router to no effect. As I am plugging and unplugging I realize that I think it's there, even though the RCA cables are NOT plugged in to the subwoofer. So I cycle the sub off and on a few times. Each time its the same. Turn on the sub (which turns on the monitors). Silent. In approx 30 sec or so, I start to hear the whistle. It "spools up" in pitch almost like a hard drive spools up, but starts higher pitched and ends up just below the upper limit of my hearing. Turn off sub and sub and monitors shut off w a pretty good thump and the whistle stops immediately.

In summary, its a very high pitched whistle or whine that is present in the monitors whenever I power up the sub, regardless of whether the amps are getting an audio signal, or just AC power, and regardless of whether they sub/monitor set is hooked up physically to the DAC, and regardless of whether the wireless is operating. Not affected by position of PVC volume control.

Any ideas? Seller is long time A'gon member w great feedback. He says it was working perfectly when shipped. I'm not asking about responsibility, I just want to see if your collective wisdom can give me anything else to try. Given the weight of the sub, I'd really don't want to start shipping the sucker around.

Thanks, all.

128x128swampwalker
vandermeulen
191 posts
 
I hate when that happens. Do you have another pair of speakers, the more similar the better, that you can "rig" up to the sub and see if it stemming from the amplifier in the sub? We are not talking rocket science here. Forget ohms for right now. Also, hook the NHT's to another amp if you can (rig). Though I doubt it is the speakers really.
shadorne's avatar
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shadorne
7,477 posts
 
It seems to be the sub - have you tried the speakers without the sub.
swampwalker's avatar
swampwalker OP
5,138 posts
 
I did use the speakers w/o the sub and they were fine. I do not have another pair of powered speakers that I can drive off the sub. They would also have to have the 1/4" phone jack input that the S-00 sub uses as output.
almarg's avatar
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almarg
9,670 posts
 
Hi Michael,

Sounds like a mystifying one. I don't have any really promising theories to offer, but here are a few things that come to mind to try:

1)Try moving the sub and monitors a goodly distance apart, if they are not presently set up that way.

2)Try putting shorting plugs on the rca inputs of the sub, especially if the previous owner was not driving them with a high impedance source such as the PVC.

3)With power off, insert and then remove a phone plug into the unused 1/4" TRS input jacks on the sub. Do that a couple of times, to make sure that their contacts are not somehow stuck in an incorrect position (which conceivably could affect things even though you are not using those inputs).

4)With power on and the whistling present, lightly jiggle the 1/4" plugs at both the sub outputs and the monitor inputs, to see if there is any effect on the whistle, due to one of them making marginal contact.

5)If you haven't already, see if the whistle occurs with only one monitor connected, and try using each of the two TRS interconnects on the one monitor.

6)Carefully compare the volume levels of the two monitors while playing a source which is either mono or centered, as a way of verifying that there isn't an open connection on one channel, on one side (+ or -) of the balanced signal pair within each TRS cable. That would cause a 6db volume disparity, and conceivably could account for the whistle as well.

If you gather from some of these suggestions that I don't have too much faith in the connection integrity of 1/4" connectors, you are right! BTW, one minor correction just fyi -- they are referred to as phone jacks, not phono jacks.

Hope that helps,
-- Al
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