Propeller Head Plaza

Technical and scientific discussion of amps, cables and other topics.

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Re: Let's compare numbers and see why mine are different from yours

Posted by john curl on September 4, 2006 at 11:47:54:
Well, this is where you and I differ. You see, just over 40 years ago, I replaced my Shure cartridge with an Ortofon, because I heard the difference while working at a hi end hi fi store. We sold Klipsch, Mac, Marantz and a few other tubed brands. I easily heard the difference, even with my Dyna PAS-3, preamp.
My customers use MC cartridges almost exclusively. In fact my Vendetta phono stage will ONLY work with an MC cartridge.
I did not know, at the time, that my Dyna was potentially slew rate limited. It wasn't a known factor when I owned it. I just found that it sounded extra soft on occasion.
Now, how did I compare and find something? Well, I designed the Levinson JC-2 preamp based on a fet-bipolar approximation of the Dyna phono stage,except that it had a fet follower at the output, AND I heard a real difference. I, now, can attribute that to TIM free design, in the Levinson, (even if it was accidental).
Now where do I get such a number such as 5V/us? Well, I measured the worst case mistracking of a number of phono cartridges and found the Ortorfon to be the worst in maximum dV/dT. AFTER, RIAA eq. by the phono stage, I got an output square wave of about 10uS, which is similar to the TIM 30 measurement that Otala and I agreed on as the minimum standard for low TIM performance. That standard was put into our paper, given at AES-NY in 1977, and later published in the JAES. It is still the standard today, I should think. Well, when you work with TIM-30 for awhile, you come to realize that 5V/us for a preamp is about right. The Dyna Pas tube preamp will not easily pass a TIM-30 signal without big-time distortion. This is the point of all this.