Probably the second most critical interface connection in the audio chain is the interface between the preamplifier and the power amplifier. The interconnecting cable can also have an impact in this interface, especially if the cable is very long or is highly capacitive.
For the best and most predictable results it is often best to use pre- and power amplifiers from the same manufacturer, as it stands to reason that these components would form the most synergistic combination together, allowing the design engineer to make the best decisions for each component.
If different makes of pre- and power amplifier are being considered it may become necessary to compare the output impedance of the preamplifier and the input impedance of the power amplifier. Generally for full frequency response it is advisable to match component impedances with a look-up factor of at least 200.
This is not to say that the components would not work together. The audio industry does have open architecture and a common interface between components. However what can happen with disparate impedances is that there could be substantial frequency response roll-off between the two components, particularly in the low frequency bass region. This is only potentially a problem when considering a tube preamplifier to drive a solid state amplifier, as many tube preamplifiers have very high output impedances, (designed to drive high input impedance tube power amplifiers) and most solid state amplifiers have low input impedances. Sometimes a high output impedance preamplifier can be very sensitive to the capacitance of the interconnect cable, which tends to roll off the high frequencies also.
The combination of tube front end for voltage amplification and a solid state power amplifier for current demands can work very well in delivering the best that both technologies have to offer. This is provided the preamplifier is designed to drive the lower input impedance that solid state amplifiers typically present to the preamplifier. The VTL TL2.5 and TL5.5 with their output impedance of approximately 200ohms are both designed to be able to drive solid state amplifiers down to 45k ohm and 20k ohm input impedance respectively, with little or no noticeable roll-off in the bass.The TL7.5 will drive any power amplifier through any reasonable length of cable with predictable performance, with only slight bass loss into the punishing 600 ohm studio standard.top
Cheers!George