This blog post was sent in by a loyal customer, R.T. reviewing the Bottlehead Crack Headphone Amplifier kit and detailing some of his very own tweaks. In outline, US-based Bottlehead has been creating valve kits for some time and have a good following. This kit is their all new output transformerless valve headphone amplifier featuring the double triode 6080 valve. This kit suits high impedance headphones. In his own words:
"Here we have details of my latest build and modding journey for the newest kit in my collection, the excellent Bottlehead Crack with Speedball Upgrade. As always big props go to the awesome guys here at HifiCollective.co.uk for the majority of the mod parts that I’ve used in the build. Also, a big thank you to the lovely Queen Eileen over the sea at Bottlehead HQ, who helped me out resolving some issues I was experiencing placing my order and for generally being lovely throughout the process. Thanks again Eileen…
For this build I have chosen to go with a slightly more modest approach to the modifications, trying where possible to keep the costs down overall. As much to reflect the modest cost and budget nature of the Crack kit itself, why spend loads on tweaks when you could simply spend the money on something better in the first place.
See my first build images below, showing the kit with the Speedball upgrade fitted. Unfortunately, I forgot to take any pictures of the kit pre-Speedball. TBH, it looked just like the pics on the Bottlehead website anyway.
In this initial build, I included a couple of bits I had left over from my earlier ANK EL34 build and modding journey. You can find the fairly long detailed story of that journey further down the Blog if you’re interested (‘Modding an ANK EL34 Level 4 C-Core – A journey down the rabbit hole’). As ever, everything is glued together with AN 6% Silver Solder. (Love this stuff)
As you can see from the pictures, the initial build includes a piece of the rather excellent IMO ‘Yarbo Audio pure silver interconnect’. I had this left over from the EL34 build and I’m using it here to connect the input RCA sockets to the volume pot. The pot is an Alps blue I had replaced early on, during the ANK work.
An initial change to the original kit-supplied parts was to swap out the original 100uf 160v electrolytic output capacitors with the excellent AN Kaisei Electrolytic. I’ve read the bumph and these are supposedly the closest you can get to the renowned Black Gates. The truth in that statement I wouldn’t know, as I don’t think I’ve ever knowingly heard some before. Personally, I love the Elna Silmac but unfortunately, these can’t be bought as a 160v version so AN is my second choice.
I also swapped out the supplied 6080 power tube for the wonderfully detailed and far sexier looking ‘Svetlana Winged C 6AS7G 6H13C Black Plates’ courtesy of the guys over at Watford Valves. I have a slew of 12AU7’s (ECC82) that have been tested through this Crack now and could go on about how each one sounds, but I’m not going to (another article for the future perhaps), needless to say, I have settled on either a Mullard (Blackburn) Short Grey Plate or an RCA 5963 Long Black Plate depending on the mood. Rich, fat, lush and involving or super balanced and detailed with astonishing extension respectively. In fact, I think the RCA is probably the most “HI-FI” sounding 12xx7 I’ve ever heard, but perhaps a bit Marmite to others.
Detailed here are the more specialist mods I’ve made. I’ll simply bullet point them below and include some pics.
- 3x Mundorf MCap MKP 2.2uf 250v bypassing each of the three Electrolytic caps on the power supply.
- 2x Mundorf MCap Supremes 1uf bypassing each of the AN Kaisei.
- 1x Triad C-7X 270ohm Choke replacing the 5w wire wound resistor between U21 and U15.
- A polished brass washer to go under the nut that holds the headphone socket in place on the chassis. Looks great IMO with the black paint job and polished gold volume knob I’ve fitted.
Some may scoff at the use of bypass on the AN output caps and TBH I was dubious myself but thought what the hell. The Kaisei Capacitors have fairly low ESR for an electrolytic so you can just give it a go and if things don’t work out you can just remove them. Simples… Needless to say, it all actually worked out quite nicely. The Mundorfs seem to have given the presentation a little bit more extension at the top end and a slightly sweeter treble. How much of that could be attributed to the other mods I couldn’t say but, hey, it all sounds great and I have noticed a small improvement overall, so I’m happy and the tweaks didn’t break the bank.
A note to potential Crack builders out there: The wires that connect to the headphone socket red and white as seen in my kit are often shown in the manual as running parallel to a bunch of other wires flat against the chassis. I found that having them like that would mean the wire closest to the wire group could pick up a 60 Hz buzz from one of the other wires in that collection: the red right-hand channel wire in my case. Be sure to lift them away from the other wires if you can, buzz gone...
To conclude… I loved building this kit. The manual is excellent and holds your hand for every step of the way. The only fiddly part is the fitting of the tiny LEDs on the B7G valve base. I feel quite proud of the finished kit, the stained waxed wood and gloss black finish to the metalwork looks awesome IMO. The kit itself sounds wonderful with a dead quiet background, bags of detail with a big soundstage. The joy of swapping around various valves in my collection so I can finally get to truly know them all intimately is great. At last, I have a headphone amp worthy of my vintage Sennheiser’s."
As ever many thanks to R.T. for this thorough write up, always exciting to see the projects your working on! If you have a project or upgrade that you'd like to share with the hi-fi community please get in touch with Nick at email@example.com
To check out the items used in this build please follow the links below: