user 37518 said:
I remember prefering the 500 ohm setting on the UA LA-610 rather than the 2K setting, but I'm probably attributing it to a change in level, the 500 ohm sounded louder which doesn't make sense since a 500ohm input will have less voltage than a 2K input as it acts as a voltage divider. So something else must have been going on there rather than just an resistor switch.
With a typical 150-200R mic, the divider effect is still in favour of the lowest impedance setting.
Let's say mic Z is 200R, input Z is 500R/2k
With the 2k position, A=0.9 or -1dB
With the 500R position, A=0.71 or -3dB, but there is 6dB more due to the turn ratio.
So, clearly, the 500R position wins in terms of sheer level, with an advantage of 4dB.
This difference is largely enough to fool the brain into thinking "better". This is normal when we think of audition as a means of detecting unseen enemies or dangers. Typically, I've found that a mere 0.5dB difference in level is perceived as "better" by non-trained listeners.
Only when levels are normalized can we really assess the more subtle differences.
I first noticed the unfavourable effects of too much loading (too low input Z) when I bought a Groove Tubes "The Brick". I thought it was extremely dull, and I traced that to the 500r input impedance, due to the hybrid NFB (voltage
and current) in the input stage. I was shocked when I learnt that Terry Manning (Ocean Ways) uses it quite often, albeit on non-essential tracks.
Of course, with most condenser mics, the effect of loading is minimal, but very noticeable on dynamics and ribbons.