New to amp measurements. Help a newbie out!

[goldark]

I'm mostly a speaker measurements guy but recently, I've been exploring all the SINAD measurements from amps and DAC's on this site. I am trying to make sense of manufacturer-given THD+N% numbers and how it relates to ASR's SINAD numbers in dB. Can one easily be converted into the other?

For example, as a case study, here are measurements of a Cambridge Audio amplifier given in THD+N%: https://audio.com.pl/images/2/5/0/5...ambridge-audio-topaz-sr30-audiocompl-lab3.jpg

How do I convert values on this graph to the typical measurements Amir gives? Such as SINAD at 5 W and 4 ohms (is this how the ASR reviews are ranked?), dynamic range numbers etc.

Are these considered "good" measurements? average? or just plain bad in relation to the ASR ranks? And what values on that graph determine this?

Thanks for any help!

 

[DVDdoug]

I don't trust manufacturers' specs. Also the manufacturer is likely to use A-weighted noise measurements which will show "better numbers" (and it can actually be more useful). Manufacturers' specs will also usually separate noise and distortion. And the manufacturer might measure S/N at full power where a higher signal makes a better number.

I would only compare specs from the same manufacturer or from the same independent lab.

With amplifiers, distortion (and frequency response) is usually better than human hearing (and better than speakers) until it's over-driven so the biggest concern is usually noise. And, hopefully the noise is also inaudible so it's not a concern either.

 

[staticV3]

THD+N [dB] is SINAD*-1.
THD+N [dB] = 20*log(THD+N [%] / 100)

The headline SINAD graph of Amir's power amp/AVR reviews is always at 5W into 4Ω. So from the graph you linked:

Looks like 0.056% THD+N which is -65dB THD+N or 65dB SINAD.

 

[goldark]

I don't trust manufacturers' specs. Also the manufacturer is likely to use A-weighted noise measurements which will show "better numbers" (and it can actually be more useful). Manufacturers' specs will also usually separate noise and distortion. And the manufacturer might measure S/N at full power where a higher signal makes a better number.

I would only compare specs from the same manufacturer or from the same independent lab.

With amplifiers, distortion (and frequency response) is usually better than human hearing (and better than speakers) until it's over-driven so the biggest concern is usually noise. And, hopefully the noise is also inaudible so it's not a concern either.

Thanks! The graph I posted was done by an independent lab and based on the poster's calculations above me, it does not have a good SINAD.