Square wave

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Joined 2003
No, no! I'm asked whether it should be square at 20 Hz, not 20 KHz!
As for the application, I'm asking because I was told the Aleph-X should be AC coupled to the source. However, using 10 uF (which is about as large quality film caps as tend to be reasonably priced) around a 10 K load (representing the Aleph-X input) in the simulator gives a pretty nasty square wave at 20 Hz. Using far larger caps means electrolytics... So, is 20 Hz too low to worry about square wave, or not?
 
Disabled Account
Joined 2003
Oops, I just noticed it's 10K between a line and ground, so 20K between the balanced lines. Still crappy 20 Hz square, see attached image.
 

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That's just what a 10uF cap does to a LF square wave. If you are trying to test an amp with 20hz square wave you have to insert the signal after the cap, "it don't mean nothin". It tells you something about the cap but little or nothing about the amp.

Also it doesn't say much about whether the 10uF cap will adversley affect actual listening. Since you are simulationg it do seruies of AC analyses with a range of cap values to see if the frequency response is acceptable to you. Next do a series of transient analyses at 100Hz and 1kHz and use a .DISTO directive (or however your simulator gets you a THD or THD+N figure) with the same cap values. See if differences in distortion are enough to concern you.

10uF IMO get resonable results in most cases. 20uF gets better, but not a lot. Perhaps not enough to justify the hassle of using the higher value.
 
And I think what people are saying is that square wave are not a partiularly meaningful way judge that. Nonetheless, the bigger the cap the more horizontal they will look (I think), but when it's horizontal enough depends on what roll off is acceptable to you. 10uF will certainly result in virtualy flat response down to 20Hz -- but a 10uF cap may affect noise and distortion up into higher frequencies (maybe even 1k) and the square wave will not give you any information about that that I'm aware of.
 
If you want a perfect square-wave response then build yourself an amp that goes from DC to infinity. Every higpass in the signal chain will add this drop on the top and bottom of a squarewave. Any lowpass will slow the rising and falling edges, that's life.
If your amp goes low enough you will be fine with your square-wave response.

Much worse than this deformation (it goes under "linear distortion" by the way) would be transient ringing.

Regards

Charles
 
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