Measuring output impedance

[barbz]

Hi,

Is there an easy way to measure the output impedance of the crackatwoa? I keep seeing comments where the 5998 tubes can reduce the OI but im not sure on what the OI is with a 6080 vs the 5998.

Ideally trying to see if I can reduce it to around the 60ohm mark to run my Final d8000's (efficient planars).

Thankyou

[Paul Birkeland]

Play a 120Hz tone into the C2A and set the output voltage for 2V (no headphones attached).  Clip lead in a 10K pot wired as a variable resistor, then turn it down until the output voltage of the C2A drops to 1V.  Remove the variable resistor and measure its resistance, and that will be equal to the output impedance of the C2A.

Going to a 5998 makes a very, very small difference in output impedance. 

If the impedance curve of the D8000 is relatively flat, it may work reasonably well with the Crack/C2A.  If it's not, a different amp would be a good idea.