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Re: Modding the MP-1?

Posted by Lew (A) on October 31, 2006 at 07:21:15

In Reply to: Modding the MP-1? posted by Legendre on October 31, 2006 at 06:04:47:

You and Ralph will hate me for this, but I plan to insert an MAT02 NPN transistor as the bottom part of the dual-differential cascode in the phono input stage, in place of the paralleled sections of 12AT7s, for more Gm and therefore more gain for my LOMC. I will leave the 12AT7 on top of the cascode and try not to change the value of its plate resistors, so as not to alter the output Z of this stage and therefore not to muck up the RIAA. I am also thinkng about trying a 12AZ7 at the output of the phono stage, in place of the 12AT7, for a lower output Z. (12AZ7 has about half the Rp of 12AT7 and a slightly higher Gm.) I am going to try raising the HV supply voltages to +/-290V, from +/-275V where it now sits, in order to be able to increase current slightly all around. Then too, I am going to play with the CCSs (two for the phono stage and one for the linestage) to make them a bit stiffer (higher Z). I am toying with the idea of replacing the pairs of 6SN7s that serve as the circlotrons with ECC99s or 5687s or 6H30s, so as to lower the output Z of the preamp, but I am trying to figure out first whether the linestage will be able to drive these tubes as well as it does the 6SN7s. On that score or on any of the above, I'd appreciate your thoughts.

Then I am doing some mods to the Allen Wright Superregulators in my HV supply, per Allen's latest recommendations (mainly to get rid of the LM317 current regulators that AW now thinks sound awful, but frankly I hear no problem from them). However, since the SuperRegs are non-stock anyway, it doesn't much relate to a production MP1.

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