The Pass Pub: The High-End Off Topic Thread

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#927
Magura said:
.... John, I think I owe you an explanation.
Remember we had a discussion some time ago, about how the square wave looked from our choke loaded amps?
Back then you were wondering why yours didn't turn out all that square after all. I claimed to not have the same issue.
I have just been running a square through a choke loaded ZV9 style amp, and mine looks just like yours did.
Magura 🙂
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O.K. Just how did it look? Or maybe you'd like to go on with that explanation? Was this non square wave at low freqs, high freqs or everywhere?
I expect it's a square wave with peak amplitude that is not a horizontal line on the scope but a rising or falling one. Somewhat like a triangle wave on top of a square wave? Similar, but I think opposite what to small of an output cap will give you?
😉
 
#928
It's a square wave with peak amplitude that is falling.

I did this test at 20Hz to 20kHz. The lower the frequency, the more pronounced the falling.

I actually tried to make a photo of it, but I will have to face the fact that I'm a total clown with a camera. (no, it's not due to a crappy camera, 100% user error).


Magura 🙂
 
#930
Well, there is one of my threads around here, maybe about 2 years ago, or maybe one of John's that deals with inductors and has a little discussion about me seeing the same on my, ZV9 bottom half-choke loaded top half, experiments.
As I said, to small of an output cap will cause the same type of effect.
I think I can come close to explaining this stuff 😱
The load beeing a choke only maintains a "good" load for the stage if the impeadance stays high. At lower freqs the choke's impeadance drops. So, if you have a sine wave propagating through your amp and you sweep the frequency you will notice the gain(Ouput Level) lowering as freq goes down. since a sign wave is a "Pure" frequency, you don't see any distortion because the impeadance is constant for a constant freq. 😉
Now the tough part :umbrella:
The square wave is subject to the same low freq rolloff (gain change) as the sine wave but a square wave is a sumation of many odd harmonics. If I remember correctly, and feel free to correct me, a 100Hz square wave would contain a sine wave of 100Hz. But, it will also contain a sine wave of 300Hz at 1/3 the amplitude, and also one at 500Hz, at 1/3 the 300Hz amplitude etc etc. It is not until you add 10 or 20 of these odd harmonics together that you actually see the waveform look square.
So, the "spectra" (all those harmonics and their levels) of the square wave is being modified by the frequency dependant loading caused by the choke that is not quite big enough. The proportion of each harmonic level (and phase also but we won't go there) needs to be correct to maintain the square shape of the wave. The fundamental (100Hz) and the lower harmonics are seeing less gain than the higher frequency ones. This causes a distortion that makes the square waves peak amplitude not horizontal on the scope. It is a high pass filter function actually. A much larger inductor will flatten things out to a lower freq 😀
 
#932
Mrs.Magura said:
Happy new year John...

Year..
1. I want to move to warmer places, damned, it is cold here in Denmark...
And second: there is some people, I really want to meet 🙂 in personally.
3. is a secret😉


Mrs. Magura😉
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Hi Mrs Magura,

1. It will be "solved" in a decade or so, you don't need to move anywhere, global warming will take care of that. 😀
2. I can guess for at least two of them 😎
3.Hm..no...I won't tell that....😀

p.s. Just kidding

All the best

Vix
 
#933
Magura said:
Hmm, something tells me that a much larger inductor, just may be a little bit unpractical 😀
Magura 🙂
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WHAT😕😕😕 Magura "may be a little bit unpractical" 😕😕😕
Didn't we know that at the start? Remember the 1000' spool of magnet wire? I think mention was made of 1H 😱
Everything is possible....to do the impossible just takes a little while longer. (Magura)

How about this, If you were to put a 100Hz sine wave input signal into your amp and it were to emerge so distorted as to look like a square wave, That would be about 33.333% THD or so. Just thought that would be an interesting point 😀
 
#934
In this case, it already is around a 1000' spool of magnet wire, see pic 😀 It's on the wrong side of 20kg

To be honest, I can't possibly hear the distortion, but I have to admit that I was a little skeptical when I first saw the square being not all that square.



Magura 🙂
 

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#935
My current amp--the one I've been developing over the last year, or so--sounds so good that I don't really care what the square wave looks like. I'm not being flip, just honest. My sweet, golden-ears wife is very happy with the sound, and that's good enough for me. Almost...

BTW, that's a great looking amp you've got there, Magura!
 
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