Bottlehead Crack

It will work but not sound it's best. The output impedance of the Crack is too high. Low frequency response will be down maybe 3 db or so

Ideally you want to sprun headphone with at least 150 ohm input impedance with the Crack.

Sine my original post here I've had my Crack for ver a year. It has the speedball and otheR mods. With the right headphones (hd600's work very well) it's a stellar headphone amp

thank you Zavato

Zavato

what is your formula for figuring the 3db down point?

I have considered the HD600s but I need them for another room as well which is not suited to their 300 ohm load.

Still the Crack is a very attractive amp and I may have to figure something out...

thanks again

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.)
Read more at http://www.innerfidelity.com/content/marvelously-addictive-bottlehead-crack#825Ssd1AvxELIUMV.99

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.

Bombaywalla,

thanks for the information I have been to those websites and know they recommend against using 32 ohm cans with the Crack unit I was just curious (and hoping for better news) as to what happens in the circuit and you cleared it up nicely. I would prefer not to tax the tubes

I have decided to buy the Sennheiser HD600s and the Crack so I can hear for myself the two together.

Phil