Beepre as a headphone amp ?

[marco08]

Hi everyone,

I'm in the middle of my bee assembly. I've started wondering if it could drive my Hifiman HE500 cans ? if it's not too weird, what would it take ? (output transformers ? other mods ?).

nothing urgent, ill complete the preamp as Doc designed it, but I can't stop imagining things.

Cheers to all

[Doc B.]

Actually we have been discussing the future possibility of a 300B headphone amp, since it would need to be somewhat different than a BeePre to be optimal.

[Paul Birkeland]

I'm in the middle of my bee assembly. I've started wondering if it could drive my Hifiman HE500 cans ? if it's not too weird, what would it take ? (output transformers ? other mods ?).

If you raised the power supply voltage to ~450 volts, added an output transformer and plate choke, then a high gain triode in front of the 300B, yes, it could power your Hifiman headphones nicely, but at this point you would essentially have Paramounts.

[marco08]

whoa, that might be a mite ambitious... I was just looking to see if I might get rid of my old Xcan and impedance match the output as is. the headphone is reasonably sensitive and not a very difficult load as HE6 or LCD2s.

I'm trying to dig a bit into circuit theory as the moment (reading through Bruce Rozenblit's tube and circuit, if anyone has other suggested books for newbies?), why would it be pertinent to raise the voltage ?

sorry for the ingenuous question.

[Paul Birkeland]

If you're going to add a step-down transformer, you'll need to swing more AC voltage, and to do that you'd want to have a little more power supply voltage available. 

[xcortes]

"If you're going to add a step-down transformer, you'll need to swing more AC voltage, and to do that you'd want to have a little more power supply voltage available"

Actually I went to the 300B curves and the 60mA point at 100V with a 5k load would provide just north 0f 300mW. My headphones are speced at 100dB/100mW so 300mW should be plentiful with a 5k:50 ohm transformer (40 ohm headphones). Unless I did something stupid (which wouldn't surprise me!).

[Paul Birkeland]

You'd want to be swinging 40V at the plate of the 300B, at low voltages, the mu of the 300B is roughly 4, so you'd want to put 10V AC into the tube.

This operation has the problems of:

DC compliance between the regulated supply and the 300B plate in attempting to get that much voltage output

Insufficient bias under the 300B for the required input voltage

Finding a 12V AC source to feed the BeePre (remember, stock or BeeQuiet has some insertion loss)

I would mention that a perfectly stock pair of Paramounts paired up with a BeePre or Submissive will have none of these issues

-PB

[xcortes]

Now I get it. Thanks.

BTW, with my recent move out of tetra amping to full rangers I have lots of amps to play with. Including three pairs of uber hot rodded Paramounts