2. amps-preamps
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Specs to look for when matching tube pre to SS amp

I would like to not make a costly mistake and learn how one determines (at least from a specifications standpoint) on how to match equipment. I have a deHavilland UltraVerve tube preamp and am looking for a new/used SS amp. The Dehavilland specs are:

Input signal: 2v RMS maximum
freq respon : 10Hz to 80kHz
noise : <80db
Max output : 8v RMS
Gain : up to 10db

The pre only uses single ended inputs and I want to match to a SS amp. My monitors are Focus Audio FS688 (85db) so I am looking at amps in the 200+ wpc range. Someone told me that I should go with an amp that has no more than @ 1.5 input sensitivity. Some of the amps that I'm looking at, GamuT and the Classe CA 2200 are in that range. I would like to consider an amp like the Blue Circle BC26MK2 as I have read it sounds somewhat like a tube amp and matches well with the Focus speakers, but it's input sensitivity rating is 4.48 to 200W. Would this create a mismatch? I believe the Pass Labs .2 series is also well over 1.5 . I do not often listen at loud volume levels. Is there more than amp input sensitivity to consider when matching to a tube preamp? I can not demo a lot of equipment, but would appreciate your suggestions. Thank you!
classical1
classicjazz
153 posts
 
I would find out what the output impedance of your preamp is, how much capacitance the output stage has and what the manufacturer's recommended minimum amplifier input impedance is. Sometimes solid state amps have input impedances as low as 10 kOhms, which cause problems with tube preamps. I had this problem with my ARC Ref 2 and Gryphon amps.
mitch2
4,223 posts
 
I believe one "rule of thumb" is the input impedance of the amp should be at least 10x the output impedance of the preamp. My McCormack DNA 500 is one of those SS amps with input impedance of only 10K ohms, and it works fine with the SF Line series preamps, which have relatively low output impedance in the range of about 100 to 300 ohms balanced. I have heard the UltraVerve is a great preamp. Good luck matching.
aball
2,018 posts
 
Input sensitivity is the input voltage required by the amp to output maximum voltage so it is related to the amp's gain. So, your preamp puts out 8V max - this means that the input sensitivity of your amp needs to be less than 8. You will of course find that basically all amps will be below 8 which means that the designers of your preamp aren't dupes. They made it so that it will work with any amp so you wouldn't have to ever worry about input sensitivity....

The output impedance of your preamp is the only spec you really need but you apparently don't have that number. I would ask deHavilland and see if they will tell you. In most cases, since the designers aren't dupes, you don't have to worry about this number either but with tube preamps, you should ask.

The rule of thumb of the amp's input impedance divided by the preamp's output impedance being 10 OR MORE is pretty good to assure that your bass doesn't get lopped off.

The cases where there are some technical mismatches are in fact quite rare (unless the designers are dupes). What happens far more frequently, IMO, is that the sound qualities don't match your desires. In this case, no numbers will help you, only luck and patience will. Good luck! Arthur
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