I am 99.99% sure that 10Meg input impedance is not the reason for the quietness of the Countryman DI.
My empirical experiments are pretty strong evidence that is hard to dispute. I don't know what is inside the Countryman other than ad copy claiming it has FET input stages, and the electronics are encased in epoxy.
In fact I learned of the trick on Gearslutz from Mr. Jim Williams, an audio engineer with a long history of improving audio equipment for a few decades including some major name recording artists from the 1970s.
All versions of the stage piano have input impedances at least 10X lower than 1Meg.
No, you're confusing input impedance with output impedance. Stage piano outputs have an output impedance.
I have several amp heads, 1 tube and 3 SS, all with 1Meg input impedance, and all are dead quiet.
As do I. But guitar amps cut off at about 5K because guitars don't do any higher, so that 5K upper limit is filtering off the noise.
The big difference is the OP wants to record his Rhodes without a guitar amp and direct into a recorder, which is full bandwidth out to 20K where the noise will now be clearly heard.
In my experiments with various DIs and amps, the pickups on the Rhodes are very sensitive to loading from input impedances. Another member here on EP forum graphed the frequency response of the pickups with varying input impedances and it is very revealing, pretty much mirrors my results. Their tone changes, and the noise varies. The pickups seem to be happy with an optimal input impedance.
Actually, I'm not confusing input and output impedances. The impedances of the suitcase pianos I referred to are the input impedances of the preamp circuitry they used, not the output impedance of the harp. Sorry if my writing wasn't clear. As for amp frequency response, all my amps are flat out to beyond 10 kHz, and not more than 2 or 3 dB down at 20 kHz. A Rhodes piano doesn't put out much signal beyond 5 kHz or so, anyway.
In a double-blind test, properly set up, I claim that no one would be able to distinguish any tonal or noise difference between a preamp having an input impedance of 1 meg ohm and 10 meg ohm. Also consider that the capacitance of the cable that connects the harp to the preamp of choice filters out some highs. If we assume a cable capacitance of 200 pF, which would account for the cable from the harp to the front panel, and the front panel to the preamp, the impedance of that capacitance at 10 kHz is about 79 k. That impedance, along with with the fairly low output impedance of the harp, makes it's just a bit hard for me to accept the idea that anyone could hear a difference between 1 and 10 meg ohm preamp input impedance. I simply don't believe it. There could be any number of reasons why the Countryman sounds better.
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