Your demand is unreasonable, sorry.
As a long time (45+ years) in the service industry, I can honestly say that any amplifier, with wide-open inputs, will be prone to hum or noise, particularly in today's world with its plethora of interference-generating devices.
Also, amplifiers, preamps, are tested with shorted inputs - you can find that fact in many Service Manuals.
Perhaps some amps have a very low input impedence internally, and will show neglegable output noise, but trust me, after servicing thousands of amps, preamps, etc., it's not always the case.
And with that said, asking for poll results from others, who have a wide range of equipment, will only show different "noise" levels, and has absolutely nothing to do with quality operation under 'normal' (source connected) operation.
Ah correct, 85 dB.
I was calculating as it was voltage ratio, instead of power ratio.
wiseoldtech - The open input noise is internally-generated. I wanted a hard test. Enough systems have passed.
Ed
Ed
It's a hard as well as a useless test, as it has no relation whatsoever with the noise floor during normal use.
My system hums without turning up the volume. Of course I have cables running all over each other and all twisted together. Need to fix that mess sometime soon.
MarcelvdG - The shorted input test is useless too. The noise floor of 16-bit PCM would cause no systems to be silent at maximum gain. 😉
Ed
Ed
I test mine at 1w as that is the most common level it's played at or below.
I can barely hear hiss with my ear pressed to the tweeter.
The amp puts out 80 wpc at clipping.
Load a cd turn it to 1w and stop the disc
I can barely hear hiss with my ear pressed to the tweeter.
The amp puts out 80 wpc at clipping.
Load a cd turn it to 1w and stop the disc
stocktrader200 - You need to play a silent but dithered track. You will hear the dither at maximum gain.
I purposely did not include source components in the test.
Ed
I purposely did not include source components in the test.
Ed
I don't understand how they place their Maggies on that thread.... right against the wall for the HT, and too close the wall where the guy is sitting.
That guy sitting on the chair.. .talk about absolutely an anti social endeavor.
Now, what would be interesting, would be to place TWO pairs of Maggies back to back... hmm... I do have the 12s in the box and the spare A5s.... I could do that. That would be interesting, place the 1.7s up front and the 12s right behind them... full range.
Nonsense.
The open input test will show how good or bad the amplifier is built.
You are not testing an amplifier gain stage in isolation.
And I know that the system is on, the LEDs are on, the router is blinking. But I can't hear anything 🙂
I disagree.
In manufacturer's Service Manuals, part of the required testing is done with inputs shorted, in order to eliminate any interference which could cause test instruments to give improper readings and make servicing difficult.
All my sources are digital, so open inputs makes no sense.
Anyway .. dead silent. Low sensitivity speakers helps.
Anyway .. dead silent. Low sensitivity speakers helps.
Suppose this test would ever get popular, and manufacturers would be forced to design their equipment for as low a noise level as possible with open input, because otherwise their equipment wouldn't sell. They would then use the smallest input shunt resistors they could get away with and noise match their input stages to that resistance.
That's the opposite of what you need for good performance during normal use. In normal use, there will be a low-impedance source connected to the input, quite possibly capacitively coupled. Using a fairly high input termination resistor will minimize the bass signal loss and phase shift across the source's output coupling capacitor. The impedance with a source connected will be lower than with an open input, which automatically leads to a different noise optimum for the input stage.
There are already two audio tests that urge manufacturers to design equipment such that it behaves suboptimally during normal use, please don't add a third...
Regarding those two tests, if you want a moving-magnet phono amplifier to get a good noise measurement in Stereophile, you have to noise optimize it for 600 ohm source impedance, for good performance in real life for 600 ohm or 1 kohm or so plus 500 mH.
If you want to sell a DAC, it has to have as high a SINAD as possible at 0 dBFS true peak, which means not keeping any headroom for intersample overshoots, which means hard clipping on many music recordings.
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