Can you say what the gain is for your Mk3.1 unit?
All the MP-1s starting with the Mk2s had 60dB of phono gain, up until the Mk3.3 which has 66 (and also lower noise). All the earlier units are updatable to the Mk3.3 with full warranty.
Thanks for the response. I lined up a good deal on a Soundsmith the Voice ebony with 1.2 mv output so I should be in good shape. I don’t typically use the atma phono stage as I have a Strain Gauge system, but it’s going in for upgrades and styli build.
Strain gauges are very interesting. I did see someone recently on another site commenting that they don't need RIAA EQ. This statement is false- they do need EQ, just not as much.
Here's the RIAA curve. The slope (the black line) is 6dB/octave. This is the rolloff that a strain gauge expresses also. The problem is that bit where the black line goes flat and the red line flattens out a little. The strain gauge doesn't do that- at 200Hz where the RIAA curve diverges from the mathematical slope the strain gauge continues at 6dB/octave. If everything worked according to the black line (which is where the zero is in the math for the curve) the strain gauge would be off by 12dB by the time it got to 2100Hz (where the next pole is) and would be off by that amount over the rest of the curve to 20KHz. In practice, the red line is what you get and so the strain gauge is off by quite a bit less than that.
What is needed mathematically for EQ is 0dB of de-emphasis to 400Hz, then a rising response of 6dB for 2 octaves, then returning to flat. The resulting curve would then allow the stain gauge to follow the RIAA curve correctly through the crucial midrange area and above.
I have owned the MP1 mk3.1 and as far as I remember it needed a 500 uV cartridge such as the Sumiko Palo Santos - I was not able to use the original Talsiman-S (200uV) with it because I of tube noise.
Perhaps better top quality NOS tubes in the input stage would improve things, but I never tried them.
Ralph Karsten uses a different input topology in the mk3.3 version of the MP1 that resulted in much lower input noise and as far as I have read will easily accept a 200 uV cartridge.
You did have to be careful with using low noise tubes on the older preamps! With any high performance tube equipment the tubes are always hand-picked. NOS tubes usually wouldn't work because people have been scouring the countryside looking for low noise examples for the last 50 years. Most of them you find these days are reject- unless you are very lucky! The Mk3.3 was an attempt to rectify this to a certain degree- since its an overall lower noise circuit the phono section is a lot easier to used with 0.2mV cartridges. But its still a fact that at least for the front end of the phono section, if you want it to be low noise you can't use NOS tubes unless you are lucky. You can use them in the final two locations though. Fortunately there are several 12AT7s that are easily had (and inexpensive) that do the job for the front end.
