How to compare these two amp power charts?

[Daniel7]

The NAD review mentions a 1kHz test tone & continuous (RMS) power. Do we know what tone is used in the ASR measure, and if it is peak vs continuous (RMS) power?

I'm trying to compare RMS power into 8 ohm loads but I'm not sure how to interpret these two charts to compare what these two amps can do.

Loxjie A30:

Loxjie A30 Amplifier Review

This is a review and detailed measurements of the multifunction Loxjie A30 power (speaker and headphone) amplifier with integrated USB DAC and Bluetooth input. It was kindly sent to me by a member and costs US $159 plus $7 shipping on Amazon. The A30 sports a high resolution and high contrast...

www.audiosciencereview.com

NAD D3020 V1:

Fig.13 NAD D 3020, distortion (%) vs 1kHz continuous output power into 8 ohms.
"The minimum distortion level was low, and the D 3020 clipped (defined as when the THD+N reaches 1%) at 58Wpc into 8 ohms (17.6dBW)"

NAD D 3020 integrated amplifier Measurements

Sidebar 2: Measurements

www.stereophile.com

 

[jasonhanjk]

They both uses 1kHz. The NAD have better spec in terms of power.
Both THD+N for both graph are quite similar if ignore it's max output power.

 

[Daniel7]

They both uses 1kHz. The NAD have better spec in terms of power.
Both THD+N for both graph are quite similar if ignore it's max output power.

I'd like to compare the two charts in order to get an apples to apples figure on RMS output. Do you know how I could do that?

 

[Matias]

First of all the Y axis scale 0.01% is -80 dB. Both graphs reach or exceed slightly below that, so they are practically the same in noise and distortion.

But max power defined by 1% THD+N which is -40 dB, one is about 30W while the other some 47W.

But the question is why are you comparing 8 ohms graphs to begin with? Most speakers nowadays are closer to 4 ohms, which is more demanding of the amplifier (higher current). You should be comparing them in 4 ohms to be more relevant imo.

 

[DVDdoug]

Amir is measuring continuous RMS. Most modern amplifiers can't put-out much more peak-power than RMS because they have regulated power supplies that don't sag very much when stressed. But I think some manufacturers measure peak power at 10% distortion or something like that to make the spec as high as possible.

With regular program material, of course the amplifier is never putting-out full-continuous power. But it's a "standard" measurement and it's a good-conservative spec. We don't mind if the amp can put-out higher occasional peaks.

I don't trust manufacturer's specs. Even the "reputable" manufacturers seem to fudge a bit.

 

[Doodski]

I'd like to compare the two charts in order to get an apples to apples figure on RMS output. Do you know how I could do that?

@ what level of THD + Noise? Give it to me either in dB or %.

 

[Sir Sanders Zingmore]

First of all the Y axis scale 0.01% is -80 dB.

How is that conversion done (I’m sure it’s a simple formula but I don’t know where to start)?

 

[Doodski]

How is that conversion done (I’m sure it’s a simple formula but I don’t know where to start)?

Use this calc.>>>

THD to dB - convert percent % to decibels dB percentage voltage % vs per cent converter THD+N total harmonic distortions calculation signal distortion factor attenuation in dB to distortion factor k in percent decibel damping - sengpielaudio Sengpiel

Calculate THD and distortions decibels dB to percentage % per cent percent voltage % vs converter and dB signal distortion THD+N total harmonic distortions factor attenuation damping - Eberhard Sengpiel sengpielaudio

www.sengpielaudio.com

 

[Daniel7]

@ what level of THD + Noise? Give it to me either in dB or %.

This raises a good question & I don't have any kind of grasp on what occurs along the range of THD, how certain thresholds might translate to listening experience.

It seems published and discussed specs are all over the board on THD. Is there a good rule of thumb or way to look at power spec charts in relation to THD?

 

[Doodski]

This raises a good question & I don't have any kind of grasp on what occurs along the range of THD, how certain thresholds might translate to listening experience.

It seems published and discussed specs are all over the board on THD. Is there a good rule of thumb or way to look at power spec charts in relation to THD?

 

[Doodski]

@Daniel7 I think 0.1% THD + Noise is a fair number for this specific use case. It's low enough you'll have your bases covered for higher frequencies and still get a good wattage figure from the amps.

 

[GXAlan]

How is that conversion done (I’m sure it’s a simple formula but I don’t know where to start)?

THD to dB - convert percent % to decibels dB percentage voltage % vs per cent converter THD+N total harmonic distortions calculation signal distortion factor attenuation in dB to distortion factor k in percent decibel damping - sengpielaudio Sengpiel

Calculate THD and distortions decibels dB to percentage % per cent percent voltage % vs converter and dB signal distortion THD+N total harmonic distortions factor attenuation damping - Eberhard Sengpiel sengpielaudio

www.sengpielaudio.com

Medium simple or medium complex depending how you look at it. Easy enough to use this website

 

[theREALdotnet]

How is that conversion done (I’m sure it’s a simple formula but I don’t know where to start)?

20*log(0.01/100) -> -80dB
10^(-80/20)*100 -> 0.01%

 

[Daniel7]

But the question is why are you comparing 8 ohms graphs to begin with? Most speakers nowadays are closer to 4 ohms, which is more demanding of the amplifier (higher current). You should be comparing them in 4 ohms to be more relevant imo.

I'm using some older Mirage 8-ohm speakers that can handle ~50w.

 

[Daniel7]

Does anyone know if there's a THD value that Amir always measures to, and if so what it would be in %?

For example on this chart how did he determine where to stop measurement on the A30?

 

[Matias]

Does anyone know if there's a THD value that Amir always measures to, and if so what it would be in %?

For example on this chart how did he determine where to stop measurement on the A30?

Visually, from where it starts to rise.

 

[solderdude]

Does anyone know if there's a THD value that Amir always measures to, and if so what it would be in %?

For example on this chart how did he determine where to stop measurement on the A30?

The measurement stopped at -15dB (20% dist @ 1kHz, 40W in 8ohm)
It is unclear why, could be limited by the gain of the amplifier (and max input voltage) or some other reason. When protection kicks in the tell tale sign is a sharp bend to the left which is not seen in this plot.
The cursor was set at -75dB (18W in 8ohm) which is around 0.02% so can assume that's where Amir draws 'a line'.

Amir usually eyeballs where the distortion starts to rise (sharply). This may not always be at the exact same distortion level.

You can easily convert level to % (and the other way around) with THIS online calculator

 

[notsodeadlizard]

Nobody counts logarithms in their minds (except geeks), so just remember the rule "10 times less percentage means -20 less decibel" and if I may say so, "threshold numbers":
1% THD is -40 dB
0.1% THD is -60 dB
0.01% THD is -80 dB
0.001% THD is -100 dB

Above 18 watts of power output, this Loxjie (how can you pronounce it at all?) flies into the wastebasket.
NAD is still OK till 48W approximately.

 

[notsodeadlizard]

This thread has said a lot about this forum.
Thank you.

 

[RayDunzl]

How is that conversion done (I’m sure it’s a simple formula but I don’t know where to start)?

THD to dB - convert percent % to decibels dB percentage voltage % vs per cent converter THD+N total harmonic distortions calculation signal distortion factor attenuation in dB to distortion factor k in percent decibel damping - sengpielaudio Sengpiel

Calculate THD and distortions decibels dB to percentage % per cent percent voltage % vs converter and dB signal distortion THD+N total harmonic distortions factor attenuation damping - Eberhard Sengpiel sengpielaudio

www.sengpielaudio.com