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Re: Hum &/or hiss from speaker
#94688 05/19/05 08:40 PM
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In reply to:

does anyone watch American Idol



NO, i am too busy watching good reality shows like the Gotti Boys and Show Dog Mom's and Dad's..

bigjohn


EXCUSE ME, ARE YOU THE SINGING BUSH??
Re: Hum &/or hiss from speaker
#94689 05/19/05 09:10 PM
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From what I've been reading in other forums, the "hiss" sound is coming from the pre-amp section of your NAD T 773 receiver. Apparently the NAD contains no muting circuitry (a kind of pure sound philosophical standpoint), and because of this there is always a hiss present. Check out this thread at Home Theater Forum for more info.

Re: Hum &/or hiss from speaker
#94690 05/19/05 09:38 PM
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Interesting....what would a person look for on a spec sheet indicating this?


Shielding and isolation are built into the build quality of the amp. There's really no technical spec for either... but they will show up good or bad in the THN+d graph of course.

As for whether or not there's gate circuitry - that would be kind of a "cheat" to make an amp sound cleaner - you'd have to look through the schematic for that.

Maybe I should talk a bit about C/L/E/G - compressor/limiter/expander/gate. I bring these up a lot, not sure if everyone "gets" them.

Limiter - we keep talking about amps going into "clipping" where the waveform peaks are cut off. A limiter works by sensing when a signal will enter clipping and adjusts the gain (volume) to prevent this. It's like having Superman ride your levels for you - when he senses the amp will go into clipping, he turns it down to, say 99% of full range, just below clipping levels.

More technically, it works by reducing levels above it's threshold by a certain ratio "crushing down" the highest levels.

Of course, this changes the divisions of output (which is a distortion of the sound). Say if program audio that's 80% as loud as the loudest sample in the program plays out at 95% of the range of the amplifier before clipping, the top end will be compressed (that top 20% of program loudness has to be made to fit into the remaining 5% of available amp headroom) hope that makes sense.

Gate - the opposite end of the spectrum. Think of a gate as, well... a gate... audio waiting on one side to get out into the speakers, but the gate doesn't open until it's triggered by a signal at least as loud as whatever it's threshold is. A hard gate cuts in and out immediately at that threshold, a soft gate fades into and out of the program material to make a smoother transistion. These are especially useful for analog sources, where tape hiss and groove swish can be nullified to pure silence in "silent" parts.

Compressor/Expander/Compander - A compressor reduces dynamic range of program audio above it's threshold. Again, using our percentages of total program loudness (I'll coin an abbreviation here for my theorical scale - TPL), say the sound of a flutes keys being worked is at 5% of TPL with the trill between a D and D-sharp note the flotist is playing is at 90% of TPL. Say the compressor is set to be 5:1 with a threshold of 50% of TPL. The sound of the keys is untouched, but the note being played is reduced to 58% of TPL (40% over threshold of 50, compressed 5:1) meaning the master gain can be cranked up to make up that 32% quieter that the note is back at 90% of TPL, but that will also bring the sound of the keys up by a relative amount. Voila - the wall of sound. Sick, isn't it?

An expander works just in reverse - expanding the dynamic range of program audio.

A compander does both in the same circuitry - for instance, most CB Radio mics are companding mics - which trade off dynamic range for high RMS (root mean square) signal strength, which gives you a more powerful signal to send out over antenna.

Bren R.

Re: Hum &/or hiss from speaker
#94691 05/20/05 12:57 AM
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No time to digest all that right now, but thank you. It's printed for further study. Now what data can I dump to make room for this......hmmmmm I din't like her much anyway...

Re: Hum &/or hiss from speaker
#94692 05/20/05 04:26 AM
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I find the more I type the more confusing I make the issue. I wobble between trying to be as accurate as possible and keeping from being technical to the point where most people's ears will smoke... and I think I walk the line badly.

Sit down over a beer with a napkin and a pen and I make a lot more sense.

Bren R.

Re: Hum &/or hiss from speaker
#94693 05/20/05 05:44 AM
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I put a glass of beer with a napkin and a pen in it under my chair about an hour ago. When are you supposed to start making sense?

Re: Hum &/or hiss from speaker
#94694 05/20/05 06:31 AM
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Someday Alice... er... Peter... bang-zoom, right to the moon!

Bren R.

Re: Hum &/or hiss from speaker
#94695 05/20/05 11:52 AM
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I have a NAD C320BEE integrated and I get a faint hiss from my M60 tweeters as well. Even when CD/DVD player are not on and volume is zero. It gets a little louder (very little) when the volume is maxed. I basically have to put my ear right next to the tweeter to hear it, so I'm not too worried about it.


Axiom M60ti Hsu VTF-2 Mk2 NAD C320BEE NAD C542 Systemdek IIX Cables by Unity Audio
Re: Hum &/or hiss from speaker
#94696 05/21/05 03:15 AM
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I have an Anthem amp that powers the M80's and use the NADT773 as a preamp. When everything else is completely disconnected including power cords and surge bar, there is a small amount of hiss just from the Anthem. When I power up the NAD the hiss becomes louder. It disappears as you move back and around 6 feet becomes pretty well unnoticable. Even the surround speakers have a slight hum to them. However slight, there is some.

From all other manufacturers, are we saying they have no sound at all when left without a source playing, even when listening up close.

From reading the other posted site discussion, this appears to be with only some of the products and not with each one.
Another variable is my main circuit breaker box is within 3 feet of the speaker and within 5 feet of the amp and receiver. Could this, being one item I couldn't shut down or unplug, cause this disturbance?

Troy


M80 VP150 4-QS8 EP600 Monitor Audio S8 NAD T 773 Anthem MCA3 II Hitachi 57" projection
Re: Hum &/or hiss from speaker
#94697 05/21/05 03:30 AM
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I just tried it again. Same results, nothing. notta, zip...quiet as death.

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