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Author Topic: Hiss in my new Sony MDR-7506 headphones???  (Read 542 times)
NU7J
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Posts: 45




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« on: October 29, 2004, 04:27:42 PM »

I purchased a pair of Sony MDR-7506 headphones after reading the excellent reviews here on eHam.net.

There is a very noticeable hiss when the headphones are plugged into any of my HF rigs, even when the AF and RF gain is fully CCW.  The hiss is not heard in my speakers or in my other set of headphones.  

I hope this isn't a normal condition, I don't think I'll be able to tolerate it.  Has anyone experienced this?  Any ideas?  

Thanks and 73,

Tom, NU7J
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W3JJH
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« Reply #1 on: October 29, 2004, 06:39:12 PM »

Assuming that you've eliminated the possiblity of snakes in your headphones, it's possible that they have extended high-frequency response that is much better than either your speaker or your other phones.  Communication headsets generally have their top end response rolled off to get rid of any such artifacts in the receiver output.
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KZ1X
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Posts: 3228




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« Reply #2 on: October 29, 2004, 07:07:26 PM »

Your headphones may be eligible for a free test.  

The test will last approximately 1 year, during which time they will be examined for correct operation.  

They will then returned to you, unless found to cause you undue stress.  

In that instance, you do not have to take them back!  They will be dealt with in an environmentally sound manner.

Just send your headphones prepaid to my callbook address.  I will verify their safe arrival via e-mail, and begin the year-long evaluation, at no charge.
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KA7GKN
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Posts: 147




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« Reply #3 on: October 29, 2004, 07:19:37 PM »

What radio are you using?
If you plug the headphones into your stereo with the volume full ccw what do you hear?

When you turn the volume up slightly what happens?

I truly doubt the phones are bad. If you bought them new unopened, they do have a warranty and likely where you bought them if less than 30 days old will exchange them..
You may want to try the phones where you bought them and compare what you hear with another pair.

I use the mdrv600 same as 7506 with a Yaesu ft990 and an Icom IC-775dsp and I never hear hiss unless I have my monitor volume level turned up when I key up and say nothing.

good luck..and they are indeed excellent headphones
Marty ka7gkn
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HB9PJT
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« Reply #4 on: October 30, 2004, 09:49:54 AM »

Of course the hiss comes from the AF amp of the TRX which is located after the volume control and not from the headphone. Maybe the rigs are pretty old or bad construction. With a moderne rig it is not a problem to use a HIFI headphone but with an old rig it is better to use special communication headphones from the rig companies.
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N5EG
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« Reply #5 on: October 30, 2004, 11:56:29 AM »

The hiss is caused by wideband noise generated in your receiver. Even a relatively new receiver such as the Yaesu FT1000MP has a lot of hiss. One company, Inrad,  http://www.qth.com/inrad/  even makes a mod for the 1000MP to reduce it. You only notice it now because the MDR-7506 has such good frequency response that it is able to reproduce the hiss.

  -- Tom, N5EG

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AA4PB
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Posts: 12892




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« Reply #6 on: October 30, 2004, 12:06:49 PM »

You'll find the high frequency noise in a lot of rigs. This is way it is generally not a good idea to use HI-FI type headphones (or speakers) but rather one of the communications types that have a more limited frequency response at both the low end and high end.

What you could do is to build a low pass filter that would prevent the high frequency stuff from getting to the headset. Something as simple as a capacitor across the headset might help. Experiment with some different values around 0.1 mfd non-polarized.
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KT8K
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« Reply #7 on: November 01, 2004, 11:43:52 AM »

Most rigs hiss, and sensitive speakers (including headphones) with really good high end response will reproduce it in an annoying way.  My Koss Pro4A headphones also have the hiss unless I do some filtering.  One thing I do that cuts the hiss is to turn up the volume on the rig and turn down the volume control on the headphones.  The higher audio volume from the rig overpowers the constant hiss of its output circuitry, and turning the volume down with the potentiometer in the headphones keeps the sound at a nice level.  If your headphones don't have an independent volume control, you can make one, either non-adjustable with a resistor across each of the audio lines, or adjustable with a small dual-gang potentiometer.
Happy listening & good reception de kt8k - Tim
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W0FM
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Posts: 2056




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« Reply #8 on: November 01, 2004, 12:21:23 PM »

I have a pair of the Sony MDR-7506's from my days in the music business.  Great sounding cans. I have used them with my FT-1000MP on a few occasions and have to say that I've never heard any hiss from this radio with the gain turned fully down.  (I have done the INRAD mods, but don't recall the hiss being an issue).

These phones DO have excellent extended high and low end reproduction like you'd expect from hi-fi phones that allow you to hear a much broader (and sometimes, annoying) range of freqs.  

I have also found that the additional "rumble" of well-reproduced heterodynes, adjacent stations, birdies, etc can become rather fatiguing after using wide response headsets for an extended period.  Sometimes, less is better.

73,

Terry, WØFM  
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