Bottlehead Crack

It uses a 12AU7A as its input stage, and a 6080 in a cathode follower configuration as its output stage. The output is capacitively coupled (the only cap in the audio path), and has an output impedance of about 120 Ohms making it an amp suited mainly for higher impedance headphones. (I'd suggest 300 Ohms and up, but some will find it fine for cans down to 100 Ohms.)
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Philjolet,
i found the above at a link from the Bottlehead website.
if you use a lower impedance headphone like the 32 Ohms you are intending, not only with you end up cranking the volume knob to get more SPL but you will also tax the circuit to output more current into your 32 Ohms headphones (to get an adequate voltage swing to create that SPL). That might work against/tax the Crack unit & it's possible that bass response will suffer. I'm not sure about the bass response being down 3dB. I'd also like to know how Zavato came to this conclusion...

the manuf is suggesting headphones with 300 Ohms impedance & higher.

Philjolet, great! let us know how the HD600-Crack combination works out. Will it be all that its Cracked out to be? Will you get high on it? ;-D

Thanks for your kind words Philjolet. :-)

Thanks Zavato. I agree with this number now. the high-pass filter is formed by a 100uF & a 32 Ohms (of the headphone) & indeed the -3dB corner of this high-pass filter = 50Hz (49.76Hz to be exact).

Philjolet, just FYI: this same FAQ #6 also states exactly what I stated - low impedance headphones will tax the Crack unit by asking it source too much current.

This FAQ section might a good one to read for you Crack owners (those that have not already read it)
http://bottlehead.com/smf/index.php?topic=4295.0