Six Acoustic inverse RIAA board - new version 1.5 measurements

Just got the new version and wow is this thing flat.

Here is the combination of their board and a LM4562 phono stage I 100% lifted from a Doug Self book. I've no need for that Teldec switch but love how precise the new version is.

DC coupled test preamp - RIAA flatness.png
Indeed - it they are upto spec the droop above 10kHz is interesting, perhaps input capacitance of the preamp.

I've just realized that it would be great if an inverse RIAA circuit could have selectable output impedance (LR) so you could more accurately mimic a particular cartridge's parameters and thus tune the loading.
Ah, yes - I'm coming to the opinion that an opamp phono preamp should use two stages, the first does the 75us pole only with only 20--25dB of gain, then a stage to do the 318us and 3180us zero and pole (with a gain of 20dB at DC). This limits the gain per stage, avoids headroom issues as neither stage attenuates in the audio band, and allows easy to calculate component values.