There we have it, again. 240uV (10Hz ...22kHz) noise with cartridge, but only 28uV with AP as source, about 18dB worse and SINAD would take a similar hit.
...
Finally strict on topic, see below. But here are some blank numbers from my LTSpice simulation at 20°C, as we are dealing with thermal noise.
Self noise of a quite standard MM 1kOhm in series with 500mH inductance, MM-pre input is 47kOhm in parallel to 350pF, resonance at 12kHz.
12k: 28nV/sqrtHz < that isn't nothing, the self noise without any amp the pickup just laying around sucking energy from the 'thermal bath' around
9k: 22nV/sqrtHz
6k: 14nV/sqrtHz
3k: 7,3nV/sqrtHz
1k: 4,5nV/sqrtHz
Impedance, to be used to calculate voltage noise as Noise current x Impedance => resulting (additional) noise voltage
12k: 45kOhm
9k: 35kOhm
6k: 22kOhm
3k: 10kOhm
1k: 3,1kOhm
Uncorrelated noise contributions sum by sqrt[ sqr(A) + sqr(B) + sqr(C) + ... ].
Example for different op amps:
NE5532 (Vn ~4nV/sqrtHz, In ~ 0,5pA/sqrtHz) at 9kHz => sqrt[ 22n^2 + (35k*0,5p)^2 + 4n^2 ]V/sqrtHZ =
28nV/sqrtHz
OPA1642 (Vn ~ 1nV/sqrtHz, In ~ 2pA/sqrtHz) at 9kHz => sqrt[ 22n^2 + (35k*2p)^2 + 1n^2 ]V/sqrtHZ =
73nV/sqrtHz
That gives, at that narrow band, some lumpy 8dB worse results for the OPA1642.
From that I concluded, that
using an OPA1642 for MM was not the very best idea in the world. I changed, sigh, my verdict one step lower, you win. Otherwise, especially for the package as it is, the product is still outstanding. Be told, the difference will be washed away by the record's self noise by factors of magnitude once the needle hits the surface.