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Amp noise floor


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There are two related measures, both are ratios that compare the power of the noise floor with the power of the signal:

Signal to Noise ratio compares the power of the noise floor present when passing a reference signal level.

Dynamic Range compares the noise floor with no signal to the maximum power signal at a specified distortion.

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Are you asking about noise, like "thermal" hiss, that you hear through the speakers while your system is on? If you hear that, it's most likely not amplifier noise. Turn off the preamp and see how audible any noise is at that point. That would be the noise from the amplifier itself.

Chances are you are hearing noise from the preamp and sources, not the amp.

The lower the background noise, the better -- the music stands out better in isolation from the background, and that's what most people want IMO. But I don't see how dynamic range gets at that. The key for me is not being able to either hear or sense background noise while music is playing. Sometimes, you don't think background noise is there until it's suddenly vanquished.

Background noise on the phono input is a separate issue, and needs another discussion. That is usually related to the output level of the cartridge in relation to the gain of the phonostage alone. For example, a phono stage gain of 40 db is plenty for a cart output of 3 mv, but inadequate and becomes noisy with a cartridge output of only 0.5 mv because you have to turn it up too far. Sixty db phono gain is needed in that case. However, 60 db of phono stage gain should NOT be confused with combined phono and line stage gain! It's easy to confuse 40 db phono gain plus 20 db linestage gain = 60 db, with 60 db for phono gain alone (that would be 80 db total gain on phono).

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I own no speakers at this point.

The hiss I'm refering to is the hiss I hear other people talk about. They buy a new amp, hook it all up and then state they can hear a hiss from x number of ft away or they can only hear a hiss if they put their ear right next to the speaker, which is often written off as somewhat of a "seashell effect" or the same effect you get if you cup your hand over your ear. Although to me that seems like it would be a different sound, but at the same time I can't imagine I would care about a slight hiss unless I could hear it from more then about 5ft.

From what I gathered, this wasn't a phono input issue.

Anyway, I am just in the learning stages here and trying to figure out what would make sense, once I do start purchasing seperates.

I'm not sure how well your first recommendation would work. Don't most people use a trigger that turns thier amp on and off with the preamp. So if you turn off the preamp you are turning off the amp. In that case I would think if you're still hearing something, find out what the voice is saying and then go see a doctor. I kid, I kid.

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From what I gathered, this wasn't a phono input issue.

It's not, if you're talking about a baseline hiss that does NOT vary with the volume control. OTOH, it is if you're talking about a high hiss level from the phono input that DOES vary with the volume control.

Don't most people use a trigger that turns thier amp on and off with the preamp. So if you turn off the preamp you are turning off the amp.

Not in my circles.[:D] But that was a common feature in vintage preamp-amp separates, for a few decades anyway. Others know more about those historical things than I do.
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For what it is worth.

A long time ago I purchased an HK amp from Frys.

Driving the home made K-Horns it was good (silent) except when the digital signal processing was switched on. That was all Dolby, HT, center channel. Everything except pure stereo. The hiss was there and annoying.

Fry's took it back, no questions asked.

Nothing in the spec sheet advised about the problem.

If you are in the market, there may be no true test in the spec sheets. You have to be in a situation where you can take it home, try it out, and return it if anything is wrong.

Wm McD

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