JBL cinema and other high sensitivity speakers hissing with pro amps - Page 3 - AVS Forum
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post #61 of 75 Old 02-20-2014, 12:23 PM
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Originally Posted by steve71 View Post

which you won't have if you hook up a powerful amp (without gain controls) to high sensitivity speakers.
Not necessarily, but you do bring up a valid point in that S/N is cumulative throughout the entire signal chain.

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post #62 of 75 Old 02-20-2014, 12:37 PM
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Maybe I should have said sub-optimal?
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post #63 of 75 Old 02-20-2014, 12:50 PM
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Originally Posted by steve71 View Post

Maybe I should have said sub-optimal?
What hasn't been touched on is the noise floor. S/N is typically measured at rated output. If that's over 100dB you certainly can't hear noise when the amp is even running 10dB below rated output. But if the amp is running at -30dB the noise floor might result in an effective S/N of only 70dB, and that would be quite audible through high sensitivity speakers. So what's just as important as full power S/N is the noise floor with the attenuators off.

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post #64 of 75 Old 02-20-2014, 01:02 PM
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Originally Posted by steve71 View Post

Sure, but don't forget that it's the system as a whole that gives a good s/n ratio. And that requires good gain structure.... which you won't have if you hook up a powerful amp (without gain controls) to high sensitivity speakers.

A pro amp might (with gain controls) not be the answer either, since I assume you'd be feeding it a -10dbu signal. Ideally you'd want a pre amp that has xlr outputs and feed that into a high quality pro amp with gain controls. Then keep your preamp turned up and govern your output with the power amps gain controls. That will give you the best gain structure and s/n ratio, but obviously it's a hassle to mess with the power amps gain controls every time you want to change the volume.

I decided to order a First Watt F3 to test out... Folks have said good things about this unit and it's use with avantgarde speakers... Lets see what happens!

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post #65 of 75 Old 02-20-2014, 02:46 PM
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Most decent modern receivers can adequately power high sensitivity speakers to the point of pain/hearing damage. You're only introducing more noise to the chain by adding electronics.

Just my $0.02 as always.


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post #66 of 75 Old 02-20-2014, 02:47 PM
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But passive speakers are boring.

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post #67 of 75 Old 02-20-2014, 03:46 PM
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" So what's just as important as full power S/N is the noise floor with the attenuators off."

is there a way to calculate the noise floor from the s/n ratio and the full power spec? or even a reasonable rule of thumb such as noise floor at 1w is pretty much the noise floor at 0?

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post #68 of 75 Old 02-20-2014, 03:51 PM
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Originally Posted by LTD02 View Post

" So what's just as important as full power S/N is the noise floor with the attenuators off."

is there a way to calculate the noise floor from the s/n ratio and the full power spec? or even a reasonable rule of thumb such as noise floor at 1w is pretty much the noise floor at 0?

You can't calculate noise floor of s/n ratio, they're two separate things. s/n ratio changes at different power levels as well.


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post #69 of 75 Old 02-20-2014, 10:11 PM
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right.

my assumption is that 1w might not be inducing much, if any additional noise relative to the absolute noise floor. perhaps that is a completely flawed assumption.

example:

let's say you've got a speaker that is 101db 1w1m sensitive.

and an amp that is -80db s/n ratio at 1w.

with 1w the speaker will be making 101db of sound and 21db of noise at 1m.

turn the volume down and the spl drops, but the 21db of noise remains.

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post #70 of 75 Old 02-20-2014, 10:27 PM
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ah!

answered my own question.

here is a bryston amp: thd+noise vs. power.

below about 10 watts in this case, distortion as a % rises at 10db per 10db decrease in power, suggesting that below 10 watts, the system is hitting its noise floor.


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post #71 of 75 Old 02-21-2014, 05:12 AM
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Quote:
Originally Posted by LTD02 View Post

ah!

answered my own question.

here is a bryston amp: thd+noise vs. power.

below about 10 watts in this case, distortion as a % rises at 10db per 10db decrease in power, suggesting that below 10 watts, the system is hitting its noise floor.


This will give low wattage performance but says nothing about hiss at zero watts signal i think.

I just ordered a First Watt F3 and Pass Labs XA 30.8 for review and ill post a review maybe next week when i get them. These class A designs should have phenomenal low wattage performance and low wattage distortion and also are designed for very low hiss (due to quality parts and schematics).

You basically could use these amps for midrange and treble (like in my speakers that have active amps built-in for woofer drivers)

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post #72 of 75 Old 02-21-2014, 07:45 AM
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"This will give low wattage performance but says nothing about hiss at zero watts signal i think."

the slope of the line indicates the absolute noise floor to me because it says that as the signal is decreasing by 10db in power, the noise as a % is increasing by 10db, so the signal is just falling into the noise floor below 10 watts.

.003% = -90.5db so if connected to a speaker with 100db 1w1m sensitivity and given 10w, the signal would be 110db and the noise would be 20db and would not decrease no matter how much the signal went down.

if the power were lowered to 1 watt and the speaker produces 100db signal, and the noise floor was still at 20db, that would be -80db. -80db is 0.01% and that is what the distortion shows for 1w.

lower again the power to 0.1 watt and the speaker produces 90db signal, and the noise floor was still at 20db, that would be -70db. -70db is 0.03% and that is what the distortion shows for 0.1w.

lower the power all the way to 0 and the speaker produces 0db signal and the noise floor is still 20db.

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post #73 of 75 Old 02-21-2014, 08:10 AM
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Quote:
Originally Posted by LTD02 View Post

"This will give low wattage performance but says nothing about hiss at zero watts signal i think."

the slope of the line indicates the absolute noise floor to me because it says that as the signal is decreasing by 10db in power, the noise as a % is increasing by 10db, so the signal is just falling into the noise floor below 10 watts.

.003% = -90.5db so if connected to a speaker with 100db 1w1m sensitivity and given 10w, the signal would be 110db and the noise would be 20db and would not decrease no matter how much the signal went down.

if the power were lowered to 1 watt and the speaker produces 100db signal, and the noise floor was still at 20db, that would be -80db. -80db is 0.01% and that is what the distortion shows for 1w.

lower again the power to 0.1 watt and the speaker produces 90db signal, and the noise floor was still at 20db, that would be -70db. -70db is 0.03% and that is what the distortion shows for 0.1w.

lower the power all the way to 0 and the speaker produces 0db signal and the noise floor is still 20db.

That's what i would imagine too but I'm not sure i can ever trust s/n curves when it comes to audible hiss especially with sensitive speakers. I have been following the advice of avs members that basically suggests going for amps made specifically made for the wattage range that I plan to use. For my speakers, 7 watts will apparently produce about 117db volumes, so a 10-20 watt amp should be more than sufficient. I am hoping that amps optimized for low wattage Class A with simple circuits will have low baseline noise.... I have some amps coming in next week to test... So we will see!

Nelson pass says his f3 is one of his best he ever made so I'll find out soon enough when they come in

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post #74 of 75 Old 02-21-2014, 11:57 PM
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Quote:
Originally Posted by LTD02 View Post

the slope of the line indicates the absolute noise floor to me because it says that as the signal is decreasing by 10db in power, the noise as a % is increasing by 10db, so the signal is just falling into the noise floor below 10 watts.
Correct. The SNR decreases because as the output power decreases, it is still being measured against the inherent noise floor of the amplifier, which is almost entirely due to the input stage devices, topology and implementation.
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post #75 of 75 Old 02-22-2014, 12:05 AM
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thanks alpha niner.


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