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Re: Thanks...

Posted by Lew (A) on November 1, 2006 at 14:22:05

In Reply to: Re: Thanks... posted by Ralph on November 1, 2006 at 13:32:01:

I say again that my motivation is to get more gain from the phono section, not in any way motivated by any problem with noise. In fact, an alternative that I have considered is to have you install the Jensen step-up transformers (or to do it myself). If the stock preamps can be driven adequately by an 0.25mV cartridge output, then the Jensens would be largely superfluous, too, except for really, really low output MC cartridges, e.g., Ortofon, which I have no plans ever to use.

Are you at liberty to reveal what have you done with the phono circuitry to increase gain in the last few years? (If the new MP1s are "even better" than the MP3, and if the MP3 can deal with an 0.25mV signal on phono, something must be different in both models.) During my rebuild (as you may recall, I bought my unit second-hand, and it had a myriad of problems after mistreatment by previous owners), I brought my MP1 up to spec as regards the Mark II version of the MP1; I am using two 12AT7s with sections paralleled to derive the "bottom" part of the input differential cascode, a single 12AT7 (one section per phase) to derive the top of the cascode, 50K plate resistors, and the Mk II RIAA circuit. At the phono output, I am using a single 12AT7 in dual-differential cascode with 50K plate resistors. Input and output amplification stages each have CCSs. I am beginning to think that the first thing I need to do is to check the condition of the tubes that are in there with regard to Gm. I can do that on my Hickok tester, albeit at the wrong voltages. I don't need a whole lot more gain, just a tad more would be nice for my Urushi.

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