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Impedance Question: Tube Preamp with SS Power Amp

Having researched this issue with the archived threads, I am still having difficulties understanding the problems of impedance mismatch between Pre and Power amps. As a budding audiophile moving onto my first separates Pre/Power, I want to know more about impedance matching. I have several questions that I hope veterian audiophiles can help me out with.

1)Is the 10:100 ratio between the output impedance of preamp and input impedance of the power amp an absolute rule?

2)What would happen if impedance mismatch do occur? Will the sound be any less satisfying?

3)I understand that Tube preamps generally have higher output impedance values compared to SS, so does that make it problematic to use it with a SS power amp even though tubed preamps are often priased over their SS counterparts?

I ask these questions because I recently purchased a tubed Preamp (Musical Design SP-2B)that has an impedance of 2K Ohms. I want to match that with a SS power amp with an impedance value of 20K Ohms. Am I cutting it too close? (exactlly 10:100 ratio) Or are all of these issues irrevalent and I should just listen to that setup and hear for myself if it would work or not? Thanks in advance for the answers.
speedracerucr
newbee
4,767 posts
 
Answers by the number -

1) No its not an absolute rule is just a general guide

2) Rolloff of the highs and lows - probably some softing of the bass impact

3) I can see no reason why these shouldn't work in theory, but most folks would really want more leeway, like money in the bank so to speak. I've successfully used a 10K impedence amp with a tubed pre in which the manufacturer recommended a minimum of 20K (which was a 40 to 1 ratio). But as a practice, to keep my options open I usually only buy amps with imput impedences of 47K or more. In your place I would want to hear the amp - preamp combo before I commit.
marakanetz's avatar
marakanetz
5,473 posts
 
Sonic Frontiers preamps have output impedance almost the same as SS preamps. Same with AudioResearch ones.
glai's avatar
glai
446 posts
 
Hovland HP100 into Pass X150. Output Imp. 2K Ohm quoted by Manufacturer but rise to 4700 Ohm towards 20Hz per stereophile test report. Input Impedance of Pass Lab approx 22K Ohm. This yields a 1/10 ratio at most freq but 4/10 at base. Theoretically should lead to base rolloff. In practise, HP 100 does not give up much base comparing to X1 preamp. 1/10 is a only a general rule. If system works, I wouldn't worry about numbers.
(If thread help, don't mind grammar)
joeabrams
132 posts
 
You can help stack the deck in your favor by keeping the interconnect cable lengths SHORT. 1 or 2m is fine, but if you had to go to 15 ft of interconnect cable with this heavy of a mismatch, I'd say fuhgedabowdit.
gs5556
1,236 posts
 
Many tube preamps will also have a higher gain, which can offset any power losses from high output impedance. High frequency roll off can be an issue if the input circuit is shunted with a filtering capacitor (R-C impedance) but amps with resistive only impedance are not affected.
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