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Old 14th April 2003, 03:49 AM   #1
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Question square wave in = square wave out

Do many amps pass the square wave test?
square wave in = square wave out

Or is the test meaningful, correlating with the ability to reproduce music (complex sine waves) well?

Generally tube amps do not pass square waves (SW) well but many play music well.

How does the (SS but somewhat tubelike mids) of Alephs fare on the ‘SW test’?
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Old 14th April 2003, 05:37 AM   #2
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Quote:
Originally posted by rick57

Or is the test meaningful, correlating with the ability to reproduce music (complex sine waves) well?

I don't think that the shape of square wave means the quality of the reproduced music.
I had a square wave in-out test for my new amp recently (see the thread named, Monolithic SuperSymmetry with Current Feedback). The test was predominantly to see the peaking of high frequency and to evaluate and control the margin of amp’s stability.

JH
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Old 14th April 2003, 06:44 AM   #3
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It is not necessary that you get a rectangular out of your amp like the one leaving your function generator.
But what the average speaker does to a rectangular is much worse than the error introduced by a bandwith limited tube amplifier.

The difference is, that the bandwith limitations of an amplifier (ans speaker !) restrict slew rate and cause tilted top and bottom of the squarewave while a speaker also introduces phase anomalies (i.e the responses of the tweeter, midrange and woofer arrive in single file).

Phase (i.e. temporal behaviour) is important for the perception of sound direction.

Look at it this way: A rectangular is quite a simple shape. If a speaker is not even able to reproduce this one properly - how in all the world could it reproduce music, which is a lot more complex ?

As always: It is important that all properties of a speaker are well balanced. It does not help to have a perfect temporal behaviour at the cost of a lot of other response anomalies.

Regards

Charles
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Old 14th April 2003, 06:48 AM   #4
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SQUARE IN.....NOT SQUARE OUT.
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Old 14th April 2003, 07:17 AM   #5
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Quote:
Originally posted by Boxbldr681

SQUARE IN.....NOT SQUARE OUT.

O... I have been thinking about square wave in and its output form.

JH
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Old 14th April 2003, 07:30 AM   #6
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Lightbulb Square Wave Testing

Hi,
I have found square wave testing extremely usefull for checking a malfunctioning (pre)amplifier.
It solved my problem with the rotten Elma balance switches f.a.
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Old 14th April 2003, 08:26 AM   #7
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Square wave testing is very useful but only if you know what you are testing and how the square wave should look like. Power amp with a nasty response can be a sign of that things aren't optimal.
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Old 14th April 2003, 08:29 AM   #8
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Quote:
Originally posted by peranders

how the square wave should look like

Briefly, how should look? Thanks.

JH
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Old 14th April 2003, 08:58 AM   #9
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The signal should look like a charging capacitor, RC-link. Disregard the disturbance in the curve. You can tolerate a slight overshoot but not too much "ringing". This is a sign of instabilty or very near it.
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Old 14th April 2003, 09:03 AM   #10
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Below I repost what I already did within another thread.
It is the response to a squarewave of 200 Hz and 10 kHz, reproduced by a system with lower and upper rolloff of 12 dB/Octave and no phase anomalities inbetween.

For the lower signal frequency the effect of the lower cutoff frequency predominates (tilted top and bottom), for the higher signal frequency it's the upper cutoff that has the largest impact on the waveshape (finite slew-rate).

But you can clearly see that there are none of the typical multiple transients, at the beginning of each half cycle, that are typical for most multiway systems.

Regards

Charles
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