That looks like it took some serious gymnastics to get everything soldered together!
Crack;Bottlehead OTL
- Thread starter ironbut
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Sounds good and has given me no trouble since built over 18 months ago.
Paladin79
Previously MOT: Cables For Less
I may need to get my BHC out one of these days for a close listen to 12AU7’s. A gentleman on here gave me a large collection for use in my PrimaLuna integrated power amp (it uses 6) but a more isolated listen would be nice.
skhan007
1000+ Head-Fier
I've got my BHC stored in the closet now, as I've been listening to bigger tube amps these days. On occasion, I think about selling it, but think I'd likely give it to one of my sons to use at college. Who knows. Maybe I'll plug it in again, as it's a fantastic sounding amp. Punches way above its class, especially with the good vintage NOS glass.
Paladin79
Previously MOT: Cables For Less
I must have 6-8 headphone amps I have stored away, I am more into tube power amps as well right now.
My power tube of preference are these KT-90’s
dstarr3
1000+ Head-Fier
One of the headphones in my collection that I'm struggling to enjoy is the AKG K712 Pro. Great soundstage and very energetic and engaging, but the highs are just so grainy. I bet my BHC would do a good job of smoothing them out, but I'm hesitant to connect the two since the K712 is only 62 ohms. But there's also a number of people in the K712 thread that talk about great success running theirs from OTL amps.
Thoughts? I always thought the BHC was best reserved only for headphones at 250-ohms and up for technical and electrical-engineering reasons beyond my comprehension. Is that right? Or should I give my 62-ohm K712 a spin on my BHC?
Another option is connecting it to my Liquid Platinum for injecting some tube magic into the headphone, but the SE out on the LP is mediocre at best and the balanced output is where the magic is, and that would require modding the headphone to connect the two. Which I'm not opposed to doing, it's just obviously more effort than just connecting it to my BHC as-is if that's reasonable to do.
Thoughts? I always thought the BHC was best reserved only for headphones at 250-ohms and up for technical and electrical-engineering reasons beyond my comprehension. Is that right? Or should I give my 62-ohm K712 a spin on my BHC?
Another option is connecting it to my Liquid Platinum for injecting some tube magic into the headphone, but the SE out on the LP is mediocre at best and the balanced output is where the magic is, and that would require modding the headphone to connect the two. Which I'm not opposed to doing, it's just obviously more effort than just connecting it to my BHC as-is if that's reasonable to do.
I plugged in my Susvara of 60ohms just to see what it was like…very quiet! Didn’t do any harm to my BHC.
HTSkywalker
Headphoneus Supremus
The BHC can even be turned on without any load attached to it so it's safe to give the K712 a spin.
Like others have said, it won't damage anything to plug in your K712 pro. However, you're correct in saying that the BHC should really only be used for high impedance headphones. When pairing headphones to amps, you should aim for a minimum of a 2-3x damping ratio, meaning the impedance of the headphones should be 2-3x the output impedance of the amplifier. The output impedance of the BHC is around 120-150 ohms, which is why it's recommended to use 250+ ohm headphones.
Using a 62 ohm headphone will result in about a 0.5 damping ratio, well below the minimum recommended. You can do it, but it probably won't sound good.
Beefy
Headphoneus Supremus
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What's going to kill you for the K712 is the current draw. Headphone power calculator says K712 needs 28 mA RMS to hit 110 dB.
Very different from something like a Focal that would also be underdamped, but wouldn't draw nearly as much current.
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HTSkywalker
Headphoneus Supremus
True as the Focal Elear & Utopia with 80 Ohms pair nicely with the BHC and the DV but still not at its best, 250+ Ohms cans are your way to go. The Sennheiser HD 600 is one of the best sounding cans with tube amps.
Just realised my BHC has been much modified and can do headphones from 100ohms with 0.3watts.
Beefy
Headphoneus Supremus
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What mods magically reduce the output impedance of an OTL amp? The 5998 tube drops it from the nominal 120R to 80R, but other than that I'm drawing a blank.
I have no idea, the amp was built for me, and these figures were suggested. Couple of pics or so.
Beefy
Headphoneus Supremus
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That looks like PSU chokes, Speedball (seemingly setup to allow different input tubes), and stupidly large output caps.
The last one is probably the one you were told would let you use low impedance phones. Indeed, that will drop the corner frequency for bass roll off with low impedance phones. But it does absolutely nothing for output impedance, damping factor, or current delivery; they are the *real* barriers to using Crack with low impedance phones.
The last one is probably the one you were told would let you use low impedance phones. Indeed, that will drop the corner frequency for bass roll off with low impedance phones. But it does absolutely nothing for output impedance, damping factor, or current delivery; they are the *real* barriers to using Crack with low impedance phones.
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