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In Reply to: RE: About Krell KAV-400xi posted by Pakard on March 07, 2008 at 05:28:55
Krell lists an output impedance of 0.17 Ohm.
DF equals speaker impedance (of 8Ohm) divided by amps output impedance.
In the case of the Krell that gives ca. 47 (a pathetic number really!).
Rotel states a DF of 1000 for RB1080. Neither states at which frequency, it should be stated at two or three (100Hz, 1Hzk, 10kHz for example). DF tends to decrease as freq. rises.
Guess the Krell might have a higher resale value tho'…
Follow Ups:
I had Rotel RB-1080 and now i bought Krell KAV-400xi so this is weird, 23DF on my 4ohms Jamo D870 speakers compared with 500DF of RB-1080 on 4ohms and all other specification are better on Rotel and the sound of Krell is incomparable better for human ear. Im much more satisfied with the Krell, definitely another class.
...and as i calculate with DF 1000 on 8Ohm the output impedance on Rotel RB-1080 is 0.008 its unbelievable...
and DF is where the Krells designer compromised (either that or he intentionally tried to make the amp sound more 'tubey'). I would guess the Rotel designer compromised mostly in the area of component and/or labour cost.
I haven't heard either amp personally so I can't say say which I would prefer. That said in my own experience any increase in control the amp has over the connected speaker/driver also increased the accuracy of the reproduction as compared to the original. Consequently my speakers are fully active, using amps with a fairly low output impedance. In a direct comparison between two identical amps, one was bridged the other wasn't, the difference between a DF of 200 and a DF of 400 was clearly audible using passive speakers. Subtle but clearly and repeatedly identifiable and in favour of the now lower-powered non-bridged amp.
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