@SIY - What do you think of the Buckeye 9040AB input impedance specified as 51k ohms in the specification yet measuring 8.4k ohms from 20Hz to 20kHz in the stereophile tests? That seems like a large variation to me. Makes me wonder if this was actually measured by Buckeye?
Could this place a greater load on source devices and potentially impact signal loss or tonal coloration?
It's an unusually large discrepancy, but as SIY says, probably not an issue, as line level connections have quite a lot of latitude. They usually run at 1 or 2Vrms (4V balanced), the player/converter/preamp has an output impedance around 100Ω (25 to 200Ω is most common), and the line level input impedance of either a pre or power amp is usually 47 to 50kΩ. That's a big difference between source and load impedance, and means that most electrical loads are relatively small.
Hypex and Purifi amp modules are different to power amps. They have both low sensitivity and low impedance, needing 10-15V input into as little as 1500 ohms for full power.
That's too much voltage
and current for most preamps, which is why integrators like Buckeye Amps use input buffers - both to provide more gain,
and to to provide the current needed by the module.
Buckeye specify 51kΩ input impedance, so it
ought to be close to that, but it's not as important as power amp / speaker matching, for example. 8.4kΩ is still much higher than 100Ω and only draws a small current. Amir has started doing what John Atkinson often does, and tests line outputs at an unrepresentative 600Ω load. This is an extreme load and often causes a drop in maximum output voltage and a small increase in distortion, but most good convertors and preamps cope well even at this level. Certainly, devices of the calibre that are likely to be used with this power amp won't be troubled.