Mar 24th, 2017
The boards are adapted to as close of input impedance match as possible when ordered (and noted on website). Many boards 210, 201A 202 etc. are very similar but differ in subtle ways because M.C. cartridge designs (even same models) varied in performance, especially in low frequency "equalization" and output level. We at APT tried to keep up with this matter and attempted to calibrate each card to within +/- 1db at 50hz (lows) for specific cartridges, but it was getting too complicated when more different M.C. designs kept coming. 201 or 202, A, B whatever, were often updated with a multi parallel input transistor board (to change impedance, slight gain, against noise parameter, etc.).
The add on "transistor" board is five more parallel transistors at the front end of the preamp to get another 4db to 6db better noise floor, which can be significant with some low output designs.
Presently all I can do is match input impedance and preamp board is typically +/- 2db within range of low frequency accuracy for most cartridges. No one has complained yet. Really the blame goes to the M.C. industry who without standards and their inconstancy to provide genuine technical specifications. Some products were certainly more correct than others (Adcom, Ortofon, Audio Technica). This is ultimately the reason why remarkable sonic opinions of M.C. performance vary tremendously among listeners. Even the arm wiring resistance can affect M.C. performance, as well as the phono cables (which does not necessarily mean more expensive phono cables are better), and other factors play a role. Fancy name preamps can also introduce sonic "flavors". Ultimately some manufacturers had to make specific transformers or preamps to try to get the best results, but the costs were very high for such unique designs.
In the final analysis the APT preamp has an equalizer switch for just the low end and an imaging control to help make the tonal balance to your taste. Also the main reason why M.C. could sound better is due to the use of a shibata or hypeline shaped tip stylus. As well the slight out of phase summing of recorded midrange which actually reduces stereo separation, but gives the impression of a more ambient field, and so "brighter" high frequency. Such a stylus can be had on conventional cartridges such as a Stanton 881s or AT 440 MLA for example. These cartridges are designed to be very close to the proper RIAA standards of equalization, and are easy to match loading impedances. Personally I think these are more consistent in sound, but moving coil designs can take it all up a notch in "transparency" effect.
It gets even more complex than this, but such is the audio business. The bottom line is give us the specs of a cartridge and adjust the input impedance which is the most crucial parameter before selling. This is explained in our listing. I will also put this commentary on our website. I hope I have helped.
Thanks
Vince