Slew rate of a WOPL

[marcok]

An other consideration folks .
Generally these measuremts are made with a pure resistive load .
It should be better to perform these tests with a complex impedance , since speakers are a
complex load . In other words the transient response measurements ( rise time , slew rate and odd harmonics )
are only a starting point to predict the behavior of your system.
I also think that is very important to test the the 3rd and 5th harmonics for two reasons :
- the human brain is very sensible to odd harmonics
- in class AB amps a resisual of odd harmonics could occur during transition from class A to B .
This is my opinion , of course .
I hope I never get bored you to this philosophical post.
Ciao
Marco

 

[laatsch55]

That's why we test out to 80k , to catch up to at least 4th order harmonics. To catch a 5th one would have to go to at least 100k. The AP will go to 120k.

 

[marcok]

Lee,
why 4th ?
For THD ? Do you use
a sine wave or a square wave generator ?
For me for THD is correct to use a sine wave and for transient response is correct to use a square wave .
A square wave , by definition , has only odd harmonics .
If you want to stimulate a system to check transient response it's necessary ( theorically ) to use a step
wave ( Heaviside fuction ) and test variables for the sfecific DUT .
Practically for audio amps you can use a square wave generator to verify rise time , slew rate and odd harmonic distorsion .
It can be possible ( approx ) consider that the slew rate is the grade of the rise time vs time .
Mathemathically the slew rate is the derivative of the rise time vs time , but it must be considered the complete
amplitude of rise time ( not 10 - 90% , but 0 - 100% )
Am I right or am I insane ? I hope this info will be helpfull and " clear "for everyone .
Ciao
Marco

 

[laatsch55]

Agreed Marco, THD&N is always a sine wave. Testing THD &N out to 80k is an accepted industry standard to catch up to 4th order harmonics of the 20k limit of human hearing. First through 4th order harmonics can contribute quite a bit to the noise figure. Thus the testing of such.

 

[marcok]

Lee,
Practically, I have tried to answer your question about transient response ( posted two days ago ) .
Ciao
Marco

 

[laatsch55]

Yep...saw that Marco....still cogitating that....

 

[Fishoz]

cogitating.....I like that, good use of the word.

 

[marcok]

I have appreciated very much .
https://en.wikipedia.org/wiki/Cogito_ergo_sum
Ciao
Marco
PS. now it's time to listen to the music and reset my philosophical thoughts.

 

[Northwinds]

cogitating.....I like that, good use of the word.

Only Brothers with a PhD in WOPLism get to bandy terms like that, I am stuck on contemplating still

 

[Gibsonian]

Approx 20V/usec Ron, governed by the minimum slew rate of the OPA134. The remainder of the circuit is limited at approximately 50V/usec making those circuit limitations second order to the OPA.

Full 350W peak to peak response at 20 KHz necessitates at least 9.4V/usec to achieve full power bandwidth. The OPA is more than 2X this and the rest of the circuit is >5X this.

The 700's can get up to 500 watts output, but probably not at 20Khz. What is the required slew rate for 500 watts?