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Thanks...

Posted by Lew (A) on November 1, 2006 at 11:08:02

In Reply to: Re: Modding the MP-1? posted by Ralph on November 1, 2006 at 08:55:46:

You wrote, "We've added resistors in the cathodes of the output circlotron to enhance current sharing, and with the regulators we have right now, the noise is so low that even the MP-3 is acceptable with less than 0.3mV at any volume- we used the ZYX Universe at RMAF with our MP-3 and that cartidge is 0.25mV. They worked great together!"

This seems to imply that the resistors in the cathodes of the output circlotron have some effect on phono gain and phono noise. I cannot imagine how this could be true, although it's conceivable that such resistors might lower overall the preamp noise. Help! However, I am having no problem whatever with noise; my preamp is DEAD silent, as are my amplifiers.

Are you actually saying that your stock MP3 has enough phono gain for a LOMC with 0.25mV output? My phono stage gain is barely adequate with my Koetsu Urushi, which makes a factory estimated 0.6mV. But even with the volume control at max setting (which is all too often the case), noise is not the problem. I just feel that dynamics are compromised. Could be the Urushi output is overstated by Koetsu, or that the 12AT7s in the phono stage are worn out, or that the input sensitivity of my amplifiers cum 22ft of balanced interconnect is low-ish.

Re the SuperRegulator: AW now recommends replacing the LF351 chips in mine with AD797 and also getting rid of the LM317s. He says the sound will improve. While I love my preamp as is and could easily just leave it alone, what the heck, I will give his suggestions a try.

I'll bite. What value resistors do you use in the cathodes of the 6SN7-based circlotron? Is the recommendation the same for both the MP3 (one 6SN7 per channel) and the MP1 (two 6SN7s per channel)?

By the way, I think my MP1 is now using a mixture of Billington Gold ECC81s, JJ 12AT7s, and NOS Mullards in the phono stage. I would take issue with your contention that "all the low noise NOS tubes were sold 3 decades ago". While it's true that some companies did sell selected low noise tubes (e.g., Mullard "10M" series, Tele 800 series, etc) back in the day, the generalization implies that all tubes coming off the line were tested for noise before sale and that there was some noise threshold beyond which tubes were held off the market. Do you think that's really the case? Could be, I guess. Anyway, noise is not the only determinant of audio happiness.

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Kimber Kable

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