Impedance match

10x is usually the recommended amount, but usually the vendor should post this in the spec.

It is instructive to look at some of the reviews at Stereophile for tube preamps. The main issue is the volume control, and response at the ends of the spectrum. This will give you a very good idea of how tube electronics will perform when feeding other electronics.

The issue for tube amps feeding speakers is more complicated because since speaker impedances tend to be complicated, with multiple peaks and valleys.

Thanks, posters!
+1, Al, for the article link.

 

noble100

    I always read and was taught by members here that the guideline was at least 10x but will work well together with anything greater, too. Identical match is definitely not correct.

With source to pre, pre to amp.
Once you have a "Output to Input" impedance ratio of say 1:10 or more, your fine.
 
We had a large participant demo at our audio society meeting, about 35-40 "golden ear'ed" audiophiles were present.
I designed a switchable on the fly input impedance changer on an excellent amp that was in a very good system.
 
This impedance changer change the "O/I" impedance ratio in 20 increments from 1:100 down to 1:5. It was at 1:5 that only two "super golden ear'ed" audiophiles "thought" they could hear a difference for the worse, but they also both said they probably couldn't pick it in a blind A/B.
All said they heard a difference at 1:3.
AC levels were checked to the mV for all ratios to be the same.

Cheers George      

georgehifi,

     Interesting experiment.  You used slightly different phrasing, but thanks for validating the general impedance matching guideline of the amp input impedance being at least 10x the output impedance of the preamp or source component (if the source is connected directly to the amp) or, in your phrasing,  an output /input ratio of 1:10.

Tim

Yes when the output impedance to input impedance (O/I)  ratio got down to 1:5 then a couple listeners said they could hear the dynamics may have been getting a little effected, but they said it was very small and don't think they could of blind A/B'd it.
But most of the 40 odd listeners said they could just detect 1:3 ratio. So a safe bet would be say 1:6 or higher.

Cheers George