What do these curves mean?

Sunsun22 · 03:48 AM

I feed my phono amp from a signal generator through an inverse RIAA circuit. It looks like the 1KHz is OK but the 10KHz and 20KHz looks very different from the input signal (the blue ones at the lower side). What do these curves mean to sound quality?

PS - The sound of this phono amp has nothing wrong and in fact, it blows away my old ASR Basis.

multisync · 7th February 2011, 04:02 AM

normal. A square wave is made up of a fundamental frequency and higher order odd frequencies that diminish in amplitude as the frequencies go higher. If you go high enough in freq on the input the output will look more and more like a sine wave. Remember the inverse RIAA is not perfect either.

Calvin · 7th February 2011, 07:20 AM

Hi,

a rectangle react very sensitive to changes in amplitude and phase response of the testes circuit.
If the rising part of the curve (left) is rounded as it shows in the upper yellow curves with rising test frequency it indicates a lowpass character.
If thats the signal You feed into Your RIAA-Preequalier it shows that Your Signal-Generator is rather limited in frequency range. Assuming perfect Prequalizing and a perfect RIAA the output should look the same as the input. Since all practical circuits show a lowpass behaviour because of bandwidth limits one would expect the rising edge of the signal to be more rounded than the input signal. The opposite is the case here, which would show in a rising amplitude response with rising frequency. So either the Prequalizer network or the RIAA seems to show a amplitude response that deviates from the normal.

jauu
Calvin

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7th February 2011, 04:02 AM	#2
multisync diyAudio Member Join Date: Jan 2008 Location: Carp	normal. A square wave is made up of a fundamental frequency and higher order odd frequencies that diminish in amplitude as the frequencies go higher. If you go high enough in freq on the input the output will look more and more like a sine wave. Remember the inverse RIAA is not perfect either.

7th February 2011, 07:20 AM	#3
Calvin diyAudio Member Join Date: Nov 2004 Location: close to Basel	Hi, a rectangle react very sensitive to changes in amplitude and phase response of the testes circuit. If the rising part of the curve (left) is rounded as it shows in the upper yellow curves with rising test frequency it indicates a lowpass character. If thats the signal You feed into Your RIAA-Preequalier it shows that Your Signal-Generator is rather limited in frequency range. Assuming perfect Prequalizing and a perfect RIAA the output should look the same as the input. Since all practical circuits show a lowpass behaviour because of bandwidth limits one would expect the rising edge of the signal to be more rounded than the input signal. The opposite is the case here, which would show in a rising amplitude response with rising frequency. So either the Prequalizer network or the RIAA seems to show a amplitude response that deviates from the normal. jauu Calvin

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