At least a ratio of 10. The output impedance of the preamp indicates its reluctance to deliver current--the higher the impedance, the harder it is to send current. The input impedance of the amp is associated with its need for current--the lower the input impedance, the more current that it requires to perform the same task.
A voltage divider effect ensues, which is minimized as the ratio of output/input impedance increases. I have heard that for good sound, 10 is the minimum for this ratio, but the higher the better.
A voltage divider effect ensues, which is minimized as the ratio of output/input impedance increases. I have heard that for good sound, 10 is the minimum for this ratio, but the higher the better.