Regarding impedance compatibility, the DNA-500 has a specified input impedance of only 10K, and the manual for the ET3 recommends a minimum load impedance of 20K. Based on some interior photos I found on the web it appears that both the ET3 and the ET3SE utilize 4 uF coupling capacitors at their outputs, so the 20K recommendation presumably applies to the ET3SE as well as to the ET3.
However, given that the impedance of a 4 uF capacitor at 20 Hz is 1990 ohms, and given that the output impedance of the preamp at frequencies above the deep bass region is undoubtedly far lower than that (the specified nominal output impedance is 100 ohms), while the resulting mismatch will produce a slight rolloff and a bit of phase shift in the bottom octave, that is unlikely to be the major contributor to the problem. More likely the single tube that is used in the unit (assuming the optional phono stage is not included) is the major culprit, as Ralph (Atmasphere) suggested. And if the optional phono stage is included, given that you are using a line-level source the single tube that is used in the preamp’s line section is what should be focused on.
Regards,
-- Al
However, given that the impedance of a 4 uF capacitor at 20 Hz is 1990 ohms, and given that the output impedance of the preamp at frequencies above the deep bass region is undoubtedly far lower than that (the specified nominal output impedance is 100 ohms), while the resulting mismatch will produce a slight rolloff and a bit of phase shift in the bottom octave, that is unlikely to be the major contributor to the problem. More likely the single tube that is used in the unit (assuming the optional phono stage is not included) is the major culprit, as Ralph (Atmasphere) suggested. And if the optional phono stage is included, given that you are using a line-level source the single tube that is used in the preamp’s line section is what should be focused on.
Regards,
-- Al