Absolutely not an expert here, hopefully someone more experienced will answer you... but I have the same issue and asked the same question...
I believe the general formula is at least 10 times, with some who think 30-40 times optimal... that is "input" impedance of your amp has to be that much greater than the "output" impedance of your preamp.
This was my link:
http://forum.audiogon.com/cgi-bin/
fr.pl?aamps&1198903877&openmine&zzElf73&4&5#Elf73
One goner mentioned a mismatch wasn't a deal breaker, only that you lose low and high end extension...and from my experience, probably microdynamics..
I just bought a tube preamp with a 3K output impedance and for the time being have it wired into the main of my budget integrated amp with a 20K input impedance....
and.. this may give me away as a total newbie.. but it sounds pretty good.. better than if I used the integrated's preamp. Of course, the tube preamp cost 3 times as much.
However, I do think I am missing a bit, especially with things like the decay, crispness of cymbals.. mostly higher frequency stuff. But it still works...
And like I said, not too experienced with this stuff....
If you're interested, you can go to this link, and read the Bound for Sound review of the M24, he uses various power SS and tube amps with the pre and gives an impression (one or two paragraph) of what various impedance matches had on the sound...
http://www.monarchyaudio.com/TubeDAC.html
Hope this helps.
I believe the general formula is at least 10 times, with some who think 30-40 times optimal... that is "input" impedance of your amp has to be that much greater than the "output" impedance of your preamp.
This was my link:
http://forum.audiogon.com/cgi-bin/
fr.pl?aamps&1198903877&openmine&zzElf73&4&5#Elf73
One goner mentioned a mismatch wasn't a deal breaker, only that you lose low and high end extension...and from my experience, probably microdynamics..
I just bought a tube preamp with a 3K output impedance and for the time being have it wired into the main of my budget integrated amp with a 20K input impedance....
and.. this may give me away as a total newbie.. but it sounds pretty good.. better than if I used the integrated's preamp. Of course, the tube preamp cost 3 times as much.
However, I do think I am missing a bit, especially with things like the decay, crispness of cymbals.. mostly higher frequency stuff. But it still works...
And like I said, not too experienced with this stuff....
If you're interested, you can go to this link, and read the Bound for Sound review of the M24, he uses various power SS and tube amps with the pre and gives an impression (one or two paragraph) of what various impedance matches had on the sound...
http://www.monarchyaudio.com/TubeDAC.html
Hope this helps.