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jman1503 29th June 2011 12:33 PM

Hiss in one channel
I am not sure this is the correct place to post this, I apologize if it is not. I own an AVR that has a slight (but very annoying) his in one channel, the front right. I would like to have any advice on how to fix it, short of taking to a repair shop. Here is what I have deduced about it:
1. It does not vary with input. It's present whether a digital signal (HDMI, SDPIF, or Coaxial), analog, or tuner.
2. It does not vary with volume. It is the same loudness when the volume is at 0 or max.
3. It is not a ground-loop noise. I think I have eliminated this possibility because my entire system is on a power conditioner.

From the reading that I have done thus far, it seems that the problem is with the amplifier. But I have read many times that this could problem could be as small as replacing a resistor, which I could fix myself. Any thoughts in how to fix this problem? Thanks in advance for the advice.

toprepairman 29th June 2011 12:46 PM

Most likely the input transistor in the power section. There's usually two of them as a differential pair, and you should replace both as the fault could be either one, and they should be as closely matched as possible, usually from the same batch is good enough.

Mooly 29th June 2011 01:10 PM

If it's pure hiss (white noise) and the noise is present with just the AVR ? (is that a audio/video receiver... dolby surround, the full works :)) then my gut feeling is that it will be a design issue and not a fault.

With just the AVR powered up and NOTHING else connected (and that means not a single lead/toslink, even fibre optic from an active DAC etc connected) is the hiss still present ?
Now a strange question but try just one speaker in the "suspect" and then the good channel. That's just to eliminate the possibility a speaker has a defective HF unit and the hiss is normal and the "quiet" channel is actually the faulty one and caused by the speaker... like I say... had to ask. That's what comes of being a service tech for too long ;)

If the hiss is "pure" then I really do suspect its just the way it is. A faulty component generating "hiss" would more than likely generate other noise as well lower down the frequency spectrum.

If the unit were genuinely faulty... by comparison with another in the same set up... then it would require detailed fault finding using a scope and standard technique of "splitting" the circuit down into havles to locate the faulty section.

jman1503 29th June 2011 03:59 PM

Thank you for your comments Henry, I will try that next week. Is it too difficult, i.e., does it require a soder?

1. Yes it is present only in the AVR, I have used all other compents/speakers with another AVR and they performed fine. And yes, it is a full surround-sound receiver: Dolby processor/decoder + amp.
2. Yes it is still present when I turn it on and nothing else is hooked up, except the power cord of course.
3. I have tried switching out speakers. I take a speaker which I know to work with other amps, then hook it up to the suspect channel: hiss. I unhook it and hook it to another channel on the same amp: no hiss. If I hook that speaker up to a completley different amp: no hiss. So it seems that my speakers are not at fault. I have tried three different types of speakers, all of which I know to be working, but tried three different types just in case.
4. So I suppose that the only solution is the fault finding method you suggested, which sounds like I do not have enough knowledge to do.

Thanks for your replies!

Mooly 29th June 2011 07:30 PM

Have you tried asking whether anyone else has this same unit and whether hiss is a problem ? Maybe even ask on some dedicated AV forum perhaps... if it's a design issue they will all do it. What is the make and model ?

toprepairman 29th June 2011 08:07 PM

Yes it will require soldering, and it is something of a fiddly job for the inexperienced, with a fair chance of getting it wrong. Perhaps it may be safer to get someone to sort it for you, could be you may not be too far from either Mooly or me?
If you do have a go then good luck.

j.man1503 21st July 2011 08:00 PM

Well, if there is a high chance of getting it wrong, then I probably will not try it. I have the front three channels being amplified by another amp right now, but would like all to be through the receiver. I did not think that it was going to be an easy fix.

To asnwer another question: I have asked a few other people that have the same amplifier as my unit, the problem seems to be an isolated one to myself. Thank you for your help guys!

Mooly 22nd July 2011 07:27 AM

Thanks for the update...

Can't really think of much else to add tbh.

I am sure you have looked at all these possibilties... nothing like a "sound enhancement" or equalizer feature or what ever it might be called that's enabled in some menu or setting somewhere and all the extra processing involved adds to the noise... but you say it's on right channel only so unless it were individually adjustable left and right then that wouldn't make sense...

It needs at least some basic tests performing on the bench I suspect to get to the bottom of this. You need a service manual too.

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