A few word to relate my Bottlehead DIY experiment with the Crack...
Woodworking is real part of the fun and is not to be neglected. Glueing this nice wood box, then applying hue and layers after layers of varnish is rewarding at the end. I applied a layer of hammered paint to the plate too.
Believe it or not, but the crack worked from the beginning, both the standard and speedballed version ! Every resistance checks, every voltage checks were dead on. Nothing needing to be corrected ! Beginner luck perhaps, probably helped by this excellent step-by-step manual !
Only surprise, when initiial power up for the speedball voltage check, the leds of the left small card did not ignite. I stopped power too soon to double check each continuity. Finding nothing wrong, I offered it a new chance, letting it more time and after ~20s of running, the leds finally ignited like on the right card.
I keeped the crack stock one day, enough to revisit part of my music collection and be stunned by its ability to drive the Senn HD650. It's my first dedicated headphone amplifier, tube moreover, experience. The spectrum delivered is wide and coherent, letting the music be delivered naturally.
Put the HD650 to the TRS output of the dac integrated amplifier and the sound seems thin, harsh, segmented in bass, medium, highs frequencies, not that pleasant indeed. I'm not saying that the amplified output of the dac is bad, I loved it a lot before the crack !
Switch the HD650 back on the crack and the image is large, the message is transparent (much appreciated on live records), embodied, smooth. On old recordings, the amp lets the defaults of the vinyl aside and delivers what matters, the music. The power is stunning : at nominal RCA output level (no attenuation on the output of the dac), the pot of the crack stays at 10-20% for a comfortable listening level.
And all that was before the speedball upgrade which drives these qualities far further ! There will be fun rediscovering my musics !!
Only a faint hum on the left channel only audible at no input level. I've read on a recent thread someone had the same problem and it was due to a faulty 12AU7. Having bought a few spare tubes while I was waiting for the kit, I'll check that when I'll start rolling them.
Nevertheless perhaps a problem when pot is at 0 during the first few minutes after the 30s power up : heavy noise on both channels. Disappears when the volume pot is turned to listening level. No reason to put the pot at 0, so it's not a real problem.
Last thing the DC voltage surge during the first 30s goes up to a 18V reading, perhaps more due to the low refresh rate of my meter. But it goes back to ~0V almost immediately. Simply wait to put the headphone in the TRS, not a huge deal.
Congratulation to the Bottlehead team for this great experience !!
My config :
- flac data source on iPhone
- iFi iDSD Nano USB dac for single-ended analog dual RCA output (
http://www.ifi-audio.com/en/nano_iDSD.html )
- speedballed Crack, 240V transformer version.
- Sennheiser HD650
