Summary:
The Pro ones sound much better when recording with mic. Focused, pro sound.
TC-D5M according to Vicky while listening in real time through headphones sound as if the singing voice is in a hollow reverb room. Still nice sound but...
Changing to both ears listening by enabling mono mode on TC-D5 Pro made a more treble sound.
Later addition:
The TC-D5 Pro II might had been listened to with phase invention.
What is the reason for the Pro ones sound much better?
Looking at the service manuals of M and Pro II they both have the same bipolar transistor at mic input stage but Pro has an input transformer.
By measuring (ac) input impedance with the Escort LCR meter and reading on schematic what the secondary sees, a guess is that the transformer might be of a very low turn ratio. Perhaps less or close to 1 to square root of 2.
Ie the inpedance of M is about double of Pros.
Typically measured 7.6KΩ transformed to 4.6KΩ input impedance on the Pros.
Ie a small ratio step up transformer.
It may be the presence of the non infinite input inductance on the Pros due to the transformer primary creating a very low or low cut off low cut filter preventing VLF entering. Also subtle HF rise. And all those advantages of signal transformers that even the best universities are a bit shy to teach.
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