Steampunk Modified Bottlehead Crack DIY Headphone Amp

If you're here you're probably a fan of steampunk, DIY audio, or hopefully both. I wanted to show off my buddy Greg's absolutely beautiful Steampunk themed Bottlehead Crack. I guess technically you might not be able to call it a Crack anymore given nearly every piece of the kit has been swapped out, but the amplifier section of the circuit the same, a simple tube buffer design. 

The Bottlehead Crack has been a popular staple for aspiring DIYers thanks to the lowish price and accessible build. Bottlehead includes step by step directions with pictures so you don't need to know how to read a schematic (although it's fairly easy for tube amps as they are typically simple circuits, so I recommend learning if you can). The stock Crack has very few parts and lacks output transformers so most can complete it in a single evening. 

That being said, many users like Greg like to customize their Bottlehead gear, so bespoke wooden bases or unique paintjobs aren't uncommon. Others choose to modify the internals to enhance performance.You will see the frequently replaced electrolytic capacitors with big honkin' film caps. Greg also designed a lovely pair of custom brackets to nestle around the Clarity Caps. 

Lots of audiophile goodies inside

You will see a small power filter near the power IEC socket, then a CRCRC high voltage power filter with Nichicon electrolytics, and near the front switch is a rectifier board. The stock crack has you mount the rectifier circuit on solder tabs around the transformer so this is a nice little improvement. Some people also elect to install ultra-fast diodes as another option. The tube sockets are replaced with the high quality CMC Teflon PTFE sockets which can help dampen tube vibration. These were directly soldered to however you can find PCBs on eBay or AliExpress to make things a little easier. CMC is also now making Bakelite versions of the socket if you are feeling especially vintage.

The stock Alpha potentiometer has been replaced by a higher quality Audio Note version, and Greg let me know he has ample real estate there to mount a larger stepped attenuator. You'll notice this Crack does not have the Speedball upgrade. While the Speedball enhances the performance of the amp as a constant current source for each channel, some people prefer the more "tubey" sound of the stock circuit. I can tell you they are two different flavors and each have their charm. I prefer to mate a Crack with the Speedball upgrade with some warm tubes and a I feel like it's a nice compromise.     

While there are plenty of improvements on the inside of the amp, the outside is the bee's knees. You'll see a polished copper chassis adorned with brass acorn nuts, a custom copper heatsink, the obligatory steampunk gears, and an old fashioned double pole knife switch. There is a reason why knife switches have been relegated to Frankenstein films and not household electronics; they are inherently unsafe and can arc when connected to high voltage. A shame as they look bad ass. This one is just for show.  

You will also notice there transformer is a little larger above. In fact Greg installed a dedicated heater transformer for the tube heater pins rather than requiring the single transformer from the kit to do all the work. 

An earlier version of the unit before the heater transformer was added

The whole unit is a work of art and has great personality. Despite being Steampunk, there were unique choices. For one much of the copper and brass is shiny and polished vs. aged/scuffed. I think it's great to not force yourself into one line of thinking; make it unique, make it you! Now Greg might have to make a pair of headphones that look equally amazing.    

For more steampunk related audio gear, check out this post.

Creator's Bio: Greg Ritacco started mis-wiring audio kits in the 1980's. Gradually fire became smoke and smoke became music. Encouraged by this, Greg briefly pursued a career in audio, first building speakers and later working for Threshold in the "lab". Family pressures and a desire to have his own back yard caused Greg to become more "serious" about his career, and as audio became the stepchild to home theater, and CD's washed vinyl away, Greg gave up and bought a Walkman. These days, he has rekindled his love of LP's and exploding electronics, built a few projects, and he and his daughter share their discoveries of new artists.

Please remember that building/modifying circuits can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. 

Tube Kits, Solid State Kits, PCBs, Transformers, and Where to Buy

I've been quite busy over the last couple of years and haven't been able to build as much as I would have liked, but now that I'm getting back into the swing of things, there are a number of DIY providers who have left the space, so I wanted to put together a list of all the great companies who still offer DIY kits, boards, transformers, etc. I hope it's of use to you, and please try to support the DIY community in any way you can. There's not much money in selling just boards, it's more of a community service in many cases. This is a growing list and I'll be adding more as time goes on. If you have one you'd like to see here, please add in the comments section.

ACTIVE BUSINESSES FOR THE DIYER

AMB Labs (Solid State board and part provider): Ti Kan has lots of great solid state options including headphone amps (desktop and portable), power amps, DACs, power supplies and more. The famous β22 (Beta 22) balanced headphone amplifier is here, as well as the portable Mini³ headphone amp which shouldn't be too hard for beginners. Tons of boards and parts available and a good forum.

Antek (Transformers): My favorite provider of toroidal transformers, Antek has fantastic pricing and a large variety of values, most of which are typically in stock. You'll find tube-friendly 6.3V and 12.6V heater secondaries here as well.

Audio Note Kits (Tube amplifiers, Preamplifiers, DACs, etc.): A little higher end than the typical DIY kit, ANK has quite a few nice offerings, most of which are based around universal chassis that work with several different configurations. Also one of the very few kit providers that offer a DAC, perhaps the only tube-based one I am aware of.  Prices range from $1,300 - $6,850 per kit, so these may be out of reach for the budding audiophile, but I still consider them a good value for the parts that are being provided. One thing to note is that the tubes are hidden within the chassis on some models (many of us like the tubes out in the open because they not only look nice but it's easier to roll them).

AudioSector (Chip Amps): Nice simple circuit PCBs designed around Texas Instruments LM3875 and LM4780 chips.

Beezar (Tube Amp Kits): Tom (Tomb on HeadFi) runs Beezar and offers great, proven designs from ECP Audio (The Torpedo I and II headphone amps) as well as other DACs and headphone amps. Tom puts together a great kit and the documentation is unbelievably good. Every step is illustrated similarly to the Bottlehead kits. Highly recommended and beginner friendly.

Bottlehead (Tube and Solid State Kit Provider): Bottlehead provides mostly tube builds, from headphone amplifiers, to low-wattage speaker amplifiers, to pre-amps, etc. This is a good company for the budding DIYer as the directions are very explicit with color photographs and the support is quite good. Most of the builds are point to point with a few small circuit boards here and there for constant current upgrades usually. I'm certain they've sold a truckload of Cracks, a very affordable headphone amp offering. Below is Tyll Hertsens of InnerFidelity (great site) building a Crack.

Cinemag (Transformers): Very nicely made signal conversion and moving coil step up transformers.

DigiKey (General Supplier): Carries all the various passive and active components you'll need to fill a circuit board (resistors, capacitors, op-amps, sockets, etc.). If they are out of a product, try Mouser.

DIYAudio Store (Solid State PCBs, Kits, Chassis): Never to be overlooked, DIYAudio.com has its own store with some great little accessory PCBs like the soft start board, a universal power supply, as well as some legendary Nelson Pass designs and big hulking chassis you'll need to house them in. Pricing is very reasonable.

DynakitParts (Tube Kits, PCBs, Transformers): Kevin at Dynakit parts is an incredible guy. You can build Dynakits just like you used to back in the 1950s thanks to his incredible efforts. Dynaco, if you aren't familiar, is likely the most legendary audio kit manufacturer of all time. The ST70, their 35 watt-per-channel amplifier is a ubiquitous favorite, and their other models, including the ST35, MKIII, MKIV, and PAS pre-amp all have a very strong following. Dynakitpart's uses the original circuits, which are excellent, but perspective buyers may also use alternative boards from a variety of producers (and will need to in the case of the PAS pre-amp and SCA35 integrated). The newly designed boards have some nice attributes in some cases, but are becoming harder to obtain lately. The Quad-caps are very cool and vintage looking, but some people prefer cap boards on the inside instead. The beautiful thing is that this is DIY, and you can do whatever you like.

Edcor (Transformers): Affordable custom-made "E I" transformers with iconic blue bells. Everything is made to order at Edcor and takes 6 weeks to get produced. If you need something immediately, Hammond may be a better bet.

ElectraPrint (Transformers): Well-made custom "E I" and moving coil transformers at reasonable prices and excellent customer service. Check out the ebay page for ready made units.

Glass Jar Audio (Solid State Kit Provider): Jeff is kind enough to assemble kits with designs from AMB, Cavelli, Toole and others. It's much easier to order through him than sourcing all the parts all over the place and the pricing is very reasonable.

Glassware Audio Design (Tube PCBs and Kits): Glassware has an impressive collection of designs, mostly around the Aikido circuit. You'll find pre-amps, phono pre-amps, headphone amps, volume attenuators, and power rectifier boards. Nice really thick PCBs that are well laid out and some offer the ability to fit bypass capacitors and large coupling capacitors (for DIYers who have strong opinions ;) ). Manuals and schematics are included with purchases. Not as friendly for beginners, start with Bottlehead unless you have some experience under your belt.

Hammond (Transformers and Chassis): Hammond offers a great array of transformers, inductors and chassis which are perfect for small to large DIY projects. Hammond is carried by a number of suppliers such as Angela, Digikey, Mouser, Allied, and others.

Magnequest (Transformers): Some of the best custom wound "E I" transformers for audio. Magnequest transformers are used in designs by Wavelength Audio, Curcio Audio, Alessandro, and other well-known makes. Check out the site for Bottlehead upgrade transformers as well.

Mouser (General Supplier): Need to populate a PCB? Mouser likely has everything you need aside from tubes and traditional tube sockets. If they don't... try Digikey.

Neurochrome (Tube and Solid State PCBs): The Modulus86 seems to be a popular design based around the LM3886 chipamp with some performance enhancements. Very low total harmonic distortion, if you're into that ;) Also a very cool 300B SET (single ended triode) PCB set is available.

Oddwatt (Tube Kits): Oddwatt is a two person team (Bruce and Rodney) offering a number of tube amplifiers and a preamplifier with simple but effective circuitry. The kits include Edcor transformers and custom chassis and PCBs. I don't know too much about the company,  but there is a nice write up on DIYAudioProjects.

Pete Millett (Tube PCBs): Tons of great designs for tube amplifiers, pre-amplifiers, headphone amplifiers and the like. Some beginner friendly designs like the Butte and Jonokuchi headphone amps, as well as expensive, esoteric amplifiers designed around unusual tube compliments. Definitely worth checking out!

Transcendant Sound (Tube Kits): I havent purchased a kit from Transcendant Sound (yet), but have heard many good things. From what I see they look to be a tremendous value. The Grounded Grid pre-amp is quite popular, and the OTL (output transformerless) tube amp designs are said to offer treble clarity rivaling solid state.

Triode Electronics (Tube PCBs and Kits): Dynaco-based amp kits as well as some guitar amplifier kits. Very nice selection of parts and tubes as well if you are building a vintage amp. Directions not quite as perfect as Tubes4HiFi or Beezar, but still very good.

Tube Audio Lab (Tube Amp Kits and PCBs): Great and not overly complex tube-based point-to-point kits and PCBs using the classic 300Bs, 45s, 2A3, etc. Parts selection based on your preferences.

Tubes4HiFi / Bob Latino (Tube PCBs and Kits): Roy and Bob run a really great DIY amp and preamp site. There are models based on the Dynaco ST70 and MKIV, as well as some higher wattage versions if you have some pretty demanding speakers or a big room to fill with sound. Lots of great kits, excellent directions for most offerings (some of the pre-amps have more basic schematics, etc).
Great products at reasonable prices from my experience.

NO LONGER PRODUCING DIY PRODUCTS / IN HIATUS

ChipAmp (Solid State PCBs and Kits): Allen at Chipamp has a fantastic array of chipamp / gainclone builds based on the LM1875, LM3886, and LM3875. He also has some great power supply, volume and switcher PCBs. Very simple and easy builds. Beginner friendly except the power amps use high amperage and would be dangerous if safety measures aren't followed carefully. UPDATE: per communications at DIYAudio.com and HeadFi.org, it seems there may be issues with order fulfillment in 2016-2017.

Classic Valve (Tube and Solid State PCBs): Geek at Classic Valve is getting out of the PCB business to shift his attention to building turn-key amplifiers. I encourage you to buy up what he has left. There are a number of very unique Dynaco boards for the PAS, ST70, MKIII and MKIV as well as power filters and other great stuff.
UPDATE: It looks like the supplier CK Magnetics is also clearing out their leftover PCBs, so grab em while you can: http://www.ebay.com/usr/ckmagnetics

DIYTube (Tube PCBs): Shannon at DIYTube is getting out of the PCB business to shift his attention to building turn-key amplifiers. You will still find excellent documentation on DIYTube.com and a semi-active forum, however the boards are no longer available.

Transcendar (Transformer Producer): Once an extremely high value "E I" transformer producer, this maker appears to no longer be producing new products.

The Fine Print: DIYAudioBlog and Zynsonix Audio, LLC does not represent or have any business affiliation with any of the above businesses or individuals. Building/modifying circuits can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

Bottlehead Crack Coppermine Edition

I’m going to guess that the Crack is Bottlehead’s all time most popular kit. A great little tube headphone amplifier at a price-point nearly anyone can afford that sounds very good for the money, it’s really hard to go wrong here. The Crack has gone up in price a little bit since its introduction 3+ years ago, but it’s still quite a value. I also highly recommend the Speedball upgrade, which replaces the plate loads on the tubes with a constant current source and brings this amp into its own with added detail and transparency. I built a Crack shortly after its release and of course replaced 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 that point-to-point Crack and decided to build a new one from the ground up with fancy parts and give it a layout that would accept that added girth.

While I normally would have turned to Keith Kirby to shape me up a new chassis, it was time for me to step up and build my own, despite not being crazy about working with wood. The first task was to figure out what the size of the top plate would be with the additional room for larger capacitors (in both coupling and power supply positions) and a pair of large-ish Hammond chokes for the power supply as well. This ended up being 12” x 12” (more than twice the stock 10x6 size!), which is perfect as sheets of metal can be ordered in 12” x 12”. Rather than go with the typical aluminum plate, 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 and comes 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 box that the plate would sit on top of. This is not the most trivial of tasks for those of us not blessed with nice power tools and a garage. So, I drew up the dimensions of the plate, where the plate would sit on top of the routed edges on the wood, noted how deep the route would be, and based on that drawing I found the appropriate sizes for the wood to be cut and added about a 1/16” of an inch for wiggle room. For the wood itself, I decided I wanted something a little more intricate (“fussy”, as someone I know would call it) than flat sides, so I went with a flat piece of pine and a piece of decorative molding and glued the two together. I then used the router to make a decorative route along the outer top edge and used a rabbeting bit to make the inner route that the plate would sit on. Four sections of this piece could then be cut at 45 degree angles to make the box. Since I was cutting the wood by hand, I used a plastic miter box and did my best to cut at a straight 45 degrees all the way down to get the corners to line up properly. Obviously, this never works out perfectly, 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 wood filler sanded down smoothly, four small wood blocks were glued to the bottom corners 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, I opted to use a copper leafing kit from Old World Art to bring the copper theme into the base. The leafing kit is a multi-step process including a red base coat, adhesive size layer, application and burnishing of the metal leaf, a sealer 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 plate size was used to determine where each hole would fall. Small holes were drilled using the drill press, larger holes for tubes and the Neutrik locking plug were punched using GreenLee punches, the extra-large holes for the capacitors were cut using hole saws on the drill press, and square holes, like for the transformer and IEC inlet were cut using a Dremel metal cutting disc. The copper is a little denser than aluminum and requires a bit more effort to cut through.

Once the chassis plate had all the holes necessary to accommodate the parts for the build, it was sanded down, starting with 80 grit sandpaper and ending with 600 grit. Next, a coat of clear satin finish was sprayed on each side to protect the copper, otherwise it tends to pick up fingerprints and oxidize. Gloves needed to be used after the sanding process so my fingers wouldn’t leave any oil on the copper. Once the clear coat was dry, parts could finally 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 parts were swapped. For the wiring, silver plated copper in PTFE/Teflon was used for power connections, including the heaters, Cardas 20.5g internally litzed copper in Teflon for the signal, and Kimber 19 gauge copper in Teflon for capacitor connections, etc. Shielded Cardas copper in Teflon was used for the input and output wiring with the copper mesh shield grounded. A few of the nice gold plated solder posts from VT4C were used in place of the tin plated ones, and short turret boards were used to handle the power supply connections, which I find a little more robust for multiple connections. The tube sockets were Teflon with gold plated copper contacts and matching miniature PCBs. Coupling caps were a combination of a 47uF Obbligato Gold Premiums and 70uF Obbligato Film in Oils, both good values for the money. The final power supply capacitor was replaced with a set of three 75uF Axon caps wired in parallel (simply because the three together were a bit cheaper than a single 220uF film cap). The volume control was a relatively low-cost Taiwanese ladder stepped attenuator. Resistors were all of the Kiwame / Koa Speers carbon film 2 watt variety. 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 few things. The Hammond 159M chokes (measuring 254 ohms resistance) replaced the 270 ohm resistors, the Obbligato Gold and Film Oil caps were wired in parallel and soldered in place of the coupling electrolytics, the pilot light was wired up to the 6.3V heater , and a few of the ground connections were moved about.  Also is the 6SN7 driver tube. A big thanks to Grainger who posted the alternate wiring information at Bottlehead which is duplicated below:

12AU7 PIN                          Wired to 6SN7 PIN

1                                                                                             2

2                                                                                             1

3                                                                                             3

4                                                                                             7

5                                                                                             N/A

6                                                                                             5

7                                                                                             4

8                                                                                             6

9                                                                                             8

I assume it is correct as it was confirmed on the forums by Caucasian Blackplate, but I make no personal guarantees ;)

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

In order to make a nice clean install for the three 75uF film capacitors in the power supply, I fabricated a piece of FRP (fiberglass reinforced plastic) with a few turrets that would sit on top of the caps and accept solder connections so they could be cleanly wired in parallel. The three caps wired in parallel give about 228uF (75x3 plus a little bit of tolerance wiggle room), very close to the 220uF electrolytic they are replacing. 

Fabricated FRP board

Fully wired up in stock configuration

After firing up the build in stock configuration and making sure it held smoke. I powered it down, removed the tubes and installed the very worthwhile Speedball upgrade. As mentioned earlier, the Speedball is a constant current source upgrade that replaces the plate loads of the input and power tubes. I also took the time to wire up the big 70uF oil filled Obbligato film caps.

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

Some nice little embellishments were a custom logo I made for the Coppermine Crack which I had engraved on a 3" wide copper plate, as well as some copper plated earrings which I attached to the top of the oil capacitors. 

Engraved plate and copper plated earrings on top of the oil caps

The final product looks and sounds great. I hope you enjoyed this build. 

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind.