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Does Input Voltage Affect SINAD Of Headphone AMP?

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Mar 16, 2019
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#1
I have a ASUS xonar u7 usb dac/amp. It has a very weak headphone amp capable of just 1.3 VRMS, so I am considering getting a separate amp like the JDS Labs Atom. On the line out, my u7 is only capable of 1 VRMS. When products are measured here, it is typically done at 2 VRMS. Would the SINAD of the Atom be different at input voltage of 1 VRMS rather than 2? I assume the output of the amp would only be half of what it would be, but does the noise level the amp adds depend on the input voltage?
 

DonH56

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#2
It can get complicated but generally the noise floor is constant so yes SINAD will drop a little. But, distortion will also drop a little, so unless you have too much hiss (noise) in your system it'll probably be OK. There are a number of threads on headphone amps so you might check them out. Hopefully someone will read this and chime in with experience and/or suggestions (I do not own a headphone amp).
 

MRC01

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#3
The noise level is often constant which is why S/N is often taken at max volume. So if the signal is halved, that should reduce S/N by about 6 dB.

1.3 Vrms will drive most headphones pretty loud. For example it will drive a Sennheiser HD 600 to about 105 dB SPL. But only if the amp can drive the current needed to swing that voltage across the load (which the ASUS may note be able to do). The advantage of running the ASUS into the Atom, is the ASUS gets a much easier load since the Atom's input impedance is at least 10 kOhm if not higher, and flat vs. frequency. Then the Atom does the harder work of driving the headphone (lower impedance, that varies with frequency), which it was designed to do.

Overall a dedicated headphone amp is likely to be a noticeable improvement, if your headphones are reasonably transparent and your music is well recorded.
 

bravomail

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#4
feeding 1V from DAC is not ideal. But Atom is very powerful so it will amplify it. It just the noise will be amplified to twice higher levels vs 2V input. Will you hear it? I don't know. I think it's worth trying. You can always later get a cheap proper DAC if you don't like it.
 
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