Better Quality Amp vs More Powerful Amp In Regards To Distortion?...

[luft262]

When comparing AVR's I know that the manufacturer's specs are probably garbage, but sometimes that is all you have to go by. I know that they usually advertise something like 0.08 % THD @ 100 watts for 2 channels at 8 ohms. I assume this is their measured THD when playing the AVR at max volume when connected to 8 ohm speakers?

My question is how does power output affect THD? If I were to play the AVR at 1/2 of max volume would that lower the THD? Basically, what I want to know is if I got an amp that is more powerful, but had a slightly higher THD might I actually experience less THD while playing music because I wouldn't be running the amps output as high at a given volume?

For example, if one had two theoretical AVR's

AVR A) THD 0.08 % THD @ 100 watts x 2 channels @ 8 ohms
AVR B) THD 0.1% THD @ 200 watts x 2 channels @ 8 ohms

Could AVR B actually display lower THD at a given volume, because it would only be running at 50% the output of AVR A? Disregarding the numbers in the example, does this line of thinking make sense? Do amps display less distortion at lower volumes? Will an amp display lower distortion if played at a lower % of it's maximum output? Along this line of thinking, if you had two amps with the same THD measurements, would the more powerful amp display less distortion at an equivalent volume output, because it would be running at less of its total power output?

Thank you for your help!

 

[wwenze]

THD+N vs power graph is the most useful, but since most makers don't provide that, the next best thing is the power with the lowest THD+N. So in the below AVR I take the output as 170W @ 0.06%

Spoiler

My question is how does power output affect THD?
- THD+N reduces with higher volume setting - The noise part reduces as you increase output voltage, until the amp starts to hit the limit and THD will increase very quickly. That's taken as the clipping point as well as the max output power while maintaining good THD. Below is an example.

Spoiler

Could AVR B actually display lower THD at a given volume, because it would only be running at 50% the output of AVR A?
- We can't tell from those two sets of numbers. We don't know why that wattage or THD was chosen. When manufacturers want to make the max power rating bigger, they will choose a predetermined THD like 0.1% or 1% or 10% and show the output power at that volume. For all we know, amplifier C could have 0.02% THD @ 100W but 0.7% at max power of 160W. In fact these are the specs for Yamaha A-S701.

0.08% vs 0.1% is minimal difference (especially when these numbers are usually not accurate reflection of real world conditions) so I would get the one with more power.

 

[luft262]

Thank you for the awesome and thorough answer! In your example, distortion started to climb in the amp above just 10 watts. Does that mean in general an amp will display less distortion at lower listening volumes? Also, when comparing AVR's within the same model family from the same brand would the models with more power potentially display less distortion at a given volume due to their greater overhead power capacity?

Thank you again.

 

[Chrispy]

Why would you assume a power rating is at max at all? It's just rated at one point on the curve....the one most convenient for the manufacturer's "rating".

 

[luft262]

Why would you assume a power rating is at max at all? It's just rated at one point on the curve....the one most convenient for the manufacturer's "rating".

Gotcha, so AVR's can produce more power than the typical numbers advertised on the box, but the distortion will probably go up. The power/distortion levels advertised are simply the best combination of power to distortion that they wanted to showcase?

 

[Chrispy]

Gotcha, so AVR's can produce more power than the typical numbers advertised on the box, but the distortion will probably go up. The power/distortion levels advertised are simply the best combination of power to distortion that they wanted to showcase?

Yes. Same for all amps.

ps Just look at measurement graphs from (mostly 3rd parties)....