@amirm The input sensitivity for 100V out is 100mV (60dB) on the SRM-006T and SRM-007T and the SRM-313. Your plot for the SRM-006T shows 2V in, 20 times the rated sensitivity. So, if you are feeding 2V in, the volume control on the Stax could not set at maximum (as it is up front of the gain stages) if you only got 80V (32dB gain) out. So the input impedance was high as a result and the performance, both the frequency response, the noise level and distortion will all be affected.
Could you run the Dashboard THD+N/SINAD plot at rated input (100mV- with the vol pot wide open) as below on say the 007t, so we can see how close to rated spec it actually is?
006
View attachment 90436
007
View attachment 90437
313
View attachment 90438
It seems strange Stax would have held onto the old definition of line level even for products made well into the 2000s.
Doesn't this also apply to the Koss E/90X? Maybe to a lesser extent as it was measured with 1V in, 10 times instead of 20 times the rated input (also 100mV due to 60dB sensitivity for 100V output):
Running the Koss at the rated 100mV input as well might show it reaching its 0.001% (-100dB) THD+N spec.