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-   -   First cycle distortion - Graham, what is that? (https://www.diyaudio.com/forums/solid-state/32758-cycle-distortion-graham.html)

petr_2009 23rd February 2021 10:42 AM

Quote:

Originally Posted by RussellKinder (https://www.diyaudio.com/forums/solid-state/32758-cycle-distortion-graham-post6545415.html#post6545415)
What do you consider to be a good number for propagation delay through an amplifier, and what do you consider a good method for measuring that?

In datasheets for some op-amps, Gdelay is indicated as time Propagation Delay: OPA633, OPA603, LT1363-LT1365, LT1227, LT1357, LT1469 and many others.

I have indicated the optimal value for power amplifiers many times; it should be no more than 100 ns with as long a linear section as possible (not less than 1 MHz).

For those who do not understand, I repeat: a musical signal is an impulse signal and each of its "hooks", every moment is the first period. Therefore, to say that Gdelay is just a signal delay and nothing more, it means nothing to understand how an amplifier works ...

scottjoplin 23rd February 2021 11:23 AM

Quote:

Originally Posted by petr_2009 (https://www.diyaudio.com/forums/solid-state/32758-cycle-distortion-graham-post6545488.html#post6545488)
I repeat: a musical signal is an impulse signal and each of its "hooks", every moment is the first period.

Please show such a signal.

TNT 23rd February 2021 11:29 AM

Yes music consists of both "impulses" and steady tones. But thats not the point, the point is that both impulses as well as steady tones are.. wait for it.... continuous.

This means that continuous proportionality is maintained for everything on a CD/LP/Tape except for the start of each track on said CD/LP/tape. And out of these three it is probably only CD that have that problem due to that the two latter ones has so much noise that the "continuous" criteria is already met before the musicians start to play. And for CD there is always a little time before music start playing that cares for the "startup" "problem"... so not to hurt the fire strike of a string or gasp for air.

If you still are confused about why the "impulses" in the music is not a valid case to support you theory, you should realise that the BW is so low in music that even a cymbal crash is perfectly continuous so nit a case for the "startup" "problem".

You have noting - sorry.

//

indra1 23rd February 2021 04:21 PM

Quote:

Originally Posted by petr_2009 (https://www.diyaudio.com/forums/solid-state/32758-cycle-distortion-graham-post6545295.html#post6545295)
... If all of this really has been widely known for many years, then I wonder why the argument ...

Because you do not understand what people say to you. You keep repeating the exact same arguments others find to be wrong or irrelevant.

RussellKinder 23rd February 2021 08:58 PM

Prop delay translates directly to phase as frequency increases, additive to whatever capacitive phase lag exists. The only problem with excessive delay is it affects the stability of the amplifier. 100ns phase delay is 1 full period at 10MHz, so the loop gain had better be below 0 dB at 5 MHz, due to delay alone. Add the 90 degrees of phase due to capacitive lag, and you have to be below zero dB by 2.5 MHz. That's if you have only a single pole.

That, to me, is the only argument for low delay through the amp: higher GBW.

Your argument for constant delay through the amp is stronger, but I think most amplifiers are fairly good, in this regard. Only phase lag or lead of EQ causes delay to wander, but the ear expects it in that case.

Think of a square wave from a digital FIR output filter, like on a CD player output. It is band-limited to 20 kHz and perfectly time coherent (constant group delay). Now, bandlimit a square wave to 20 kHz with an RC filter. It no longer has constant group delay, but it is still correct to the ear, because the phase corresponds to the band-limiting. Studies have shown that people can't hear phase, which makes sense if you consider how the ear works.


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