Thd+n

[zesla]

Hi there.

Hope my meaning makes sense to you guys.

I know the meaning of THD but I do not know how to work with it?

For instance For an op-ampl like LM3875 the datasheet says:
"The LM3875 is a high-performance audio power amplifier
capable of delivering 56W of continuous average power to
an 8Ω load with 0.1% THD+N from 20Hz to 20kHz."

Or regarding the TL072 the THD is 0.01 %.

Ok so the lower the THD the lower harmonic distoration and the better amplifier but any other thing (formula or graph in the datasheet) to be considered?

P.S What +N means too?

Thanks beforehand

 

[audioguru]

A power amplifier does a lot of work and an opamp does almost no work so a good opamp has lower distortion than a good power amp.
An OPA134 opamp has distortion of only 0.00008%.
N is noise (hiss).

 

[crutschow]

THD is just the value of the amplifier's harmonic distortion to a single sine-wave frequency (there's also Inter-Modulation Distortion, IM, which is the result of one sine-wave frequency affecting another, but that value is not often given expect for good high fidelity equipment). You don't do anything with it, other than use it to compare with other amplifiers. Obviously the lower this value is, the better.

N is the noise. It's difficult to separate the distortion products from the amplifier noise when doing the distortion measurement so it usually includes both or THD+N.

Edit: The distortion and power output are two of the most important parameters for audio power amplifiers. Another consideration is the power supply voltage required to obtain the rated power. Some amps can operate closer to the supply rails and thus dissipate less power for a given output power.

 

[audioguru]

The lousy old LM324 and LM358 opamps have 3% of crossover distortion. The datasheets do not say how much crossover distortion but show how to reduce it.

The lousy old 741 opamp has a very high amount of noise (hiss) but it is not mentioned on its datasheet.