Hi Jim,
Nice to see you back here.
The input impedance of the Rocket 88R is 150K (150,000 ohms), which is easily high enough to make impedance compatibility a non-issue with virtually all preamps.
Ideally the input impedance of the amp should be 10 or more times greater than the output impedance of the preamp, at the frequency for which preamp output impedance is highest. Otherwise audible frequency response irregularities MIGHT result, depending mainly on how the output impedance of the preamp varies as a function of frequency.
If, as is often the case, the highest output impedance of the preamp across the audible frequency range cannot be determined, and only a nominal output impedance is specified (which is often based on a frequency of 1 kHz), I suggest using a ratio of 50 or more, and preferably 75. As Erik alluded to, many tube preamps and some solid state preamps use a coupling capacitor at their outputs, which can cause their output impedance to be much higher at deep bass frequencies than at higher frequencies.
The same principles apply, btw, to assuring impedance compatibility between source components and preamps. Although the issue seems to arise less often in those cases.
Best regards,
-- Al
Nice to see you back here.
The input impedance of the Rocket 88R is 150K (150,000 ohms), which is easily high enough to make impedance compatibility a non-issue with virtually all preamps.
Two local guys, though, expressed ... [that] if I insisted on mixing the technologies, put the tubes in front.This is incorrect. While there are many exceptions, in general an impedance compatibility issue has the greatest likelihood of occurring if the output of a tube-based component is driving the input of a solid state component. That is because more often than not tube-based components have higher output impedances than solid state components, and more often than not solid state components have lower input impedances than tube-based components.
Ideally the input impedance of the amp should be 10 or more times greater than the output impedance of the preamp, at the frequency for which preamp output impedance is highest. Otherwise audible frequency response irregularities MIGHT result, depending mainly on how the output impedance of the preamp varies as a function of frequency.
If, as is often the case, the highest output impedance of the preamp across the audible frequency range cannot be determined, and only a nominal output impedance is specified (which is often based on a frequency of 1 kHz), I suggest using a ratio of 50 or more, and preferably 75. As Erik alluded to, many tube preamps and some solid state preamps use a coupling capacitor at their outputs, which can cause their output impedance to be much higher at deep bass frequencies than at higher frequencies.
The same principles apply, btw, to assuring impedance compatibility between source components and preamps. Although the issue seems to arise less often in those cases.
Best regards,
-- Al