Bottlehead Crack W Speedball Calligraphy
I’m going to guess that the Crack is Bottlehead’s all timemost popular kit. A great little tube headphone amplifier at a price-pointnearly anyone can afford that sounds very good for the money, it’s really hardto go wrong here. The Crack has gone up in price a little bit since itsintroduction 3+ years ago, but it’s still quite a value. I also highlyrecommend the Speedball upgrade, which replaces the plateloads on the tubes with a constant current source and brings this amp into itsown with added detail and transparency. I built a Crack shortly after its release and of coursereplaced a number of the parts with racier versions and it sounded quite good.Years later, I reminisced how much fun it was to put together thatpoint-to-point Crack and decided to build a new one from the ground up withfancy parts and give it a layout that would accept that added girth.
Bottlehead Crack – “The Review”. You know what’s going on inside and can easily add to it and improve it either on your own or using the add-n “Speedball” kit from Bottlehead. Can anyone recommend a good DAC to go along with my Crack w/speedball? I was thinking the Schitt Bifrost. Bottlehead Crack OTL for sale. Up for sale is a Bottlehead Crack OTL headphone amp with Speedball upgrade. Custom built with a walnut finish. Tube set and power cord are supplied. It also has the resistor mod described here: htt. The Marvelously Addictive Bottlehead Crack. Tyll Hertsens| Sep 18, 2012 Bottlehead Crack OTL DIY Headphone Amp ($279) Over the years, I've stopped by the Bottlehead booth at shows to say 'Hi!' The Crack+Speedball has a great, colored, tube sound to it while the Soloist is exact, precise, crisp and very detailed. Which one I prefer depends.
While I normally would have turned to Keith Kirby to shapeme up a new chassis, it was time for me to step up and build my own, despitenot being crazy about working with wood. The first task was to figure out whatthe size of the top plate would be with the additional room for largercapacitors (in both coupling and power supply positions) and a pair oflarge-ish Hammond chokes for the power supply as well. This ended up being 12” x12” (more than twice the stock 10x6 size!), which is perfect as sheets ofmetal can be ordered in 12” x 12”. Rather than go with the typical aluminumplate, I spent a few extra bucks and went with a 12” x 12” x 0.1” copper plate.The copper provides even better grounding and conduction than aluminum andcomes with a nice natural color. Despite the fluctuating metal market, a copper plate this size isn't too bad at about $40.
The next chassis-related task was to create the wooden boxthat the plate would sit on top of. This is not the most trivial of tasks forthose of us not blessed with nice power tools and a garage. So, I drew up thedimensions of the plate, where the plate would sit on top of the routed edgeson the wood, noted how deep the route would be, and based on that drawing Ifound the appropriate sizes for the wood to be cut and added about a 1/16” ofan inch for wiggle room. For the wood itself, I decided I wanted something alittle more intricate (“fussy”, as someone I know would call it) than flatsides, so I went with a flat piece of pine and a piece of decorative moldingand glued the two together. I then used the router to make a decorative routealong the outer top edge and used a rabbeting bit to make the inner route thatthe plate would sit on. Four sections of this piece could then be cut at 45degree angles to make the box. Since I was cutting the wood by hand, I used aplastic miter box and did my best to cut at a straight 45 degrees all the waydown to get the corners to line up properly. Obviously, this never works outperfectly, so that’s what wood filler is for.
| Wood frame for metal plate 'gravity' mount |
| Wood frame corner detail |
Once the box was assembled with wood glue and the woodfiller sanded down smoothly, four small wood blocks were glued to the bottomcorners to provide adequate surface area for the EAR damping feet to be placed.For the finish, rather than simply staining the wood like I normally would, Iopted to use a copper leafing kit from Old World Art to bring the copper themeinto the base. The leafing kit is a multi-step process including a red basecoat, adhesive size layer, application and burnishing of the metal leaf, asealer coat, application of an antique top-coat, and then another sealer coat. The nice thing about copper leaf is it's incredibly cheap; a set of 25 sheets runs less than $10.
| Old World Art Leafing Kit |
| Red base coat |
| Copper leafing process |
Once complete, it looks like the texture you would find on an old frame on a painting in an art gallery.
| Copper leaf after burnishing |
| Copper leaf over the whole frame |
Now the copper plate could be cut, punched, drilled, Dremeled,etc. to hold all the parts in place. The layout used to plan the initial platesize was used to determine where each hole would fall. Small holes were drilledusing the drill press, larger holes for tubes and the Neutrik locking plug werepunched using GreenLee punches, the extra-large holes for the capacitors werecut using hole saws on the drill press, and square holes, like for thetransformer and IEC inlet were cut using a Dremel metal cutting disc. Thecopper is a little denser than aluminum and requires a bit more effort to cutthrough.
Once the chassis plate had all the holes necessary toaccommodate the parts for the build, it was sanded down, starting with 80 gritsandpaper and ending with 600 grit. Next, a coat of clear satin finish was sprayedon each side to protect the copper, otherwise it tends to pick up fingerprintsand oxidize. Gloves needed to be used after the sanding process so my fingerswouldn’t leave any oil on the copper. Once the clear coat was dry, parts couldfinally be fastened onto the plate.
| Copper plate after sanding and satin finish |
Aside from the PT-3 transformer from Bottlehead, a little bit of the wiring, and the Speedball upgrade, all other partswere swapped. For the wiring, silver plated copper in PTFE/Teflon was used forpower connections, including the heaters, Cardas 20.5g internally litzed copperin Teflon for the signal, and Kimber 19 gauge copper in Teflon for capacitorconnections, etc. Shielded Cardas copper in Teflon was used for the input andoutput wiring with the copper mesh shield grounded. A few of the nice goldplated solder posts from VT4C were used in place of the tin plated ones, andshort turret boards were used to handle the power supply connections, which Ifind a little more robust for multiple connections. The tube sockets wereTeflon with gold plated copper contacts and matching miniature PCBs. Couplingcaps were a combination of a 47uF Obbligato Gold Premiums and 70uF ObbligatoFilm in Oils, both good values for the money. The final power supply capacitorwas replaced with a set of three 75uF Axon caps wired in parallel (simplybecause the three together were a bit cheaper than a single 220uF film cap).The volume control was a relatively low-cost Taiwanese ladder steppedattenuator. Resistors were all of the Kiwame / Koa Speers carbon film 2 wattvariety. The knob was a solid aluminum one with set screw from Kilo. Finally,the switch was a nice little brass plated 3A DPDT that was made for guitars.
Wiring up the unit went just like a stock unit aside for a fewthings. The Hammond 159M chokes (measuring 254 ohms resistance) replaced the 270 ohm resistors, the Obbligato Goldand Film Oil caps were wired in parallel and soldered in place of the couplingelectrolytics, the pilot light was wired up to the 6.3V heater , and a few ofthe ground connections were moved about. Also is the 6SN7 driver tube. A big thanks toGrainger who posted the alternate wiring information at Bottlehead which isduplicated below:
12AU7 PIN Wiredto 6SN7 PIN
21
47
65
86
| Initial parts installation on the copper plate |
Even though the stock Bottlehead PT-3 looks great as-is, I wanted to try something a little different for this build, so I opted to use a transformer cover from VT4C. The transformer cover base had to be trimmed to fit the PT-3, but it's a perfect fit length and width wise.
| Bottlehead PT-3 sitting on top of VT4C transformer cover base |
| Fabricated FRP board |
| Fully wired up in stock configuration |
Here's a shot of the completed amplifier sitting on the copper leafed base. I really love the look of the copper color and black on this build.
| Completed Coppermine Crack |
Crack W A R Full Album
| Engraved plate and copper plated earrings on top of the oil caps |
