Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Ahhhhh!!

Posted by MBK (A) on March 8, 2002 at 23:10:56

In Reply to: Re: TDA1541A sin(x)/x, I/V ... do I get this right posted by Elso Kwak on March 8, 2002 at 14:24:40:

... my clouds are lifting.

I misinterpreted the sin(x)/x function as a consequence of HF intermodulation and selective cancellation, when in fact it's due to the phase shift that becomes more and more severe until it reaches 180 degrees at 44.1 kHz. Or is it.

And the two filters of you and Thorsten have different priorities:

Thorsten is concerned to correct the phase shift and thus the sin(x)/x rolloff. This rolloff would be no concern if it wasn't for its cause, the phase shift itself. Thorsten's design is more lenient on the HF cutoff.

Your filter leaves the phase shift untouched but places the emphasis on rolling off the HF, and since you're using a gentle slope filter, you ave to start at lower frequencies and have even more loss at 20 kHz.

Two questions arise: phase correction AND gentle rolloff in one actually speak for the use of the infamous transformer solution which makes me feel uneasy because I have no experience in the ins and outs of transformers in audio (and just playing around is $$$ here - although I picked up some mini mains transformers CT 220V >> 9V for a couple $ to play with and see if they pass any audio at all :-) not for use on the Rotel at first for sure, haha). Alternately one could also use an active delay filter such as used in crossover time alignment for speakers, combined with any choice of HF rolloff filter...

My brain starts smoking here...

Cheers,

MBK

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