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The stock Alpha potentiometer has been replaced by a higher quality Audio Note version, and Greg let me know he has ample real estate there to mount a larger stepped attenuator.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. 

Octal OTL DIY Tube Headphone Amp

Another day, another headphone amp :) One of my life's pleasures is digging around on eBay for exciting finds, whether it be obscure vintage tube equipment or interesting/useful PCBs. This article covers the latter, a very nicely made PCB which features an octal (8-pin) tube OTL headphone amp circuit. Specifically, this is an Aikido input with a White Cathode Follower output, based on John Broskie's design. The circuit is designed to power most headphones, including those with a 32 ohm impedance. This is relatively uncommon with OTL headphone amps, which usually get along best with headphones ~300 ohms.

Top and Bottom of PCB

The tube compliment is a pair of  6BX7 or 6BL7 output tubes, a pair of 6SN7 input tubes, and a 5AR4 rectifier... because tube rectifiers are fashionably old school. Using all these tubes requires a hefty transformer, the 8.6lb.Hammond 272JX, which has a 5V, 6.3V and 600V secondary outputs. Yes, 600V, so this is not an amp for beginners. 

One can utilize the 6BX7 or 6BL7 tubes by switching two pairs of jumpers on the board, or the circuit can be configured to only work with one of the two tubes, but you can select between 32 and 300 ohm outputs using the jumpers. I personally chose the 6BL7 tubes and two different impedance outputs. 

One nice thing is that getting pairs of vintage 6BX7 / 6BL7 tubes is pretty reasonable ... $25-30 a pair for many different brands and vintages. Same for the 6SN7. You can get the GTB variants which are built to a slightly higher spec. For the 5AR4 you'd probably want to get new construction from Sovtek or similar. Guitar center is a good source. 

All the stuff on the BOM is of great quality: WIMA film caps, Vishay resistors, Nichicon electrolytics... all the good stuff. I ended up digging around the workroom to see what I had first... mostly Kiwame and carbon comp resistors, hand matched as carbon comp values can vary by 10% or more. Film caps are compact Panasonics. For the power resistors I think I went with Koa Speers as the Vishays were oddly overpriced on Mouser.

PCB populated with the smaller components

Ceramic tube sockets soldered in place

For the larger film caps, I wanted to incorporate some of the EVO oil Mundorfs. The sizing is tough, as the Mundorfs are fairly compact, but wide, and the chassis is about 3" tall, so some unique fitting was required. As most of the area underneath the caps on the circuit board doesn't have any traces running through it, I used a cutting disc and Dremeled away the area on each side... this would give an extra 1/4" to 1/2" height lost from the PCB and standoffs for extra clearance. I drilled a hole on each side of the PCB as well so a zip tie could hold each cap in place. 

The chassis I selected is from IAG DIY Tube Audio Products. He lists his chassis on ebay and on his website. Hand-made in the USA and built like a tank. The chassis gauge is relatively thick, but aluminum so easy to work with. I chose to cover up the pretty polished aluminum with painters tape to try and prevent any scratches.

Using a step drill bit to make holes in chassis

Using a Greelee punch to make the holes for the headphone outputs

Dremelled out area for IEC power inlet

I accidentally inverted the drawing when punching the holes, so we have an extra hole here. No big deal, it can be covered with a 1 1/8" Hillman hole cover.

Interior of the chassis

The populated PCB slips right in place. There aren't too many wire connections needed, just the transformers, pot controlled RCA input, and headphone output. Shielded Cardas 2 x 21.5 was used for the input and output (as they no longer make the 2 x 24 for some reason). I also wired up a pilot light to the 6.3V heater. The Hammond comes with a 115V and 125V primary. Typically you use the one that closest matches your house's voltage. As mine is 120V on the dot, I used the 125V as it didn't really matter. You dial in the voltage via the two adjustable resistors inside anyway.

When adjusting the 300V secondary, I noticed R24 was dissipating a bit too much heat and starting to smoke. Per the seller, R24 has been changed to 22K, so I went ahead and swapped that out.

Ignore the power wiring in this image, the ground is isolated on the board and is wired differently

By default for a tube amp, I wired in a filtered IEC outlet, however these are incompatible with this design as there is a ground isolation circuit built in. Once everything was corrected, I ensured the secondaries were dialed in correctly, but was getting a high DC offset. Chatting with the designer, he suggested just loading the circuit with 32 ohms on each channel. Upon measuring this, all was well. The unit started up without any issue and sounds excellent.

Completed headphone amp rear

I had a nice little brass tag made for the nameless amp, simply calling it "High Voltage OTL Aikido Octal" as the seller's eBay name is HVforless and it employs an Aikido circuit. The front features a 4 pin XLR for convenience with a shorted left and right ground.

Completed headphone amp front

You can get vintage driver tubes for this amp on the cheap, so that's another nice bonus.

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. 

WHAMMY Pass Labs DIY Headphone Amp

Wayne Colburn of PASS Labs was kind enough to release a new DIY headphone amp circuit into the wild, the WHAMMY, standing for Wayne' Headphone Amplifier Must Make Yourself. It's a nice simple build, no need to match parts or make adjustments, so it's perfect for the budding DIY builder. It's also inexpensive. The PCB, parts and chassis should be under $200 without much effort. Jim Tiemann aka 6L6 of DIYAudio has been kind enough to coordinate the project and has been instrumental in making it accessible. Having a headphone amp of this caliber available at this price is an incredible opportunity and I hope many can take advantage of it. If you're not familiar, Pass Labs is very

You can read more about the project here and boards can be purchased for a very reasonable price at DIYAudio. And you can learn more about the circuit design by watching this Youtube video:

Wayne Colburn of Pass Labs, the designer of the WHAMMY

I'll be briefly walking through my own build. I encourage you to also check out Jim Tiemann's build as it is more granular. My parts choices are also going to be outside of the standard BOM to some extent and will be more expensive, but DIY is fun because you have the freedom to make some unique choices without deviating from the original circuit.

As I knew I would have a little bit of extra headroom in the chassis I'd be using, so I added a piece of Dynamat between the board and the transformer just for a little bit of extra vibration damping. There's electrical tape over some of the larger contacts to prevent any shorting with the aluminum on top of the Dynamat.

Dynamat mounted on the PCB

After this, the power supply components were populated on the board. Normally, you would populate the small components all across the board such as the diodes, resistors, etc., however in this case populating the power components first allows you to test the power supply and ensure it is running properly and within tolerance before moving on. Review Jim's write-up for additional information on the measurements.

Please note the snubber capacitor (C20) should be an X-type, so you might see X1 or X2 in the model number. Before buying the capacitor, check the datasheet to ensure it is X1 or X2 rated. The lead spacing is 22.5mm. I personally used part 594-2222-336-10224 from Mouser. The PSU caps are Nichicon "For Audio"... for whatever that's good for ;)

Power supply populated and ready for testing

After the power supply is tested, fully disconnected, and the caps allowed to fully discharge, I moved along to populate the smallest parts first. If you've read my blog in the past, you'd know I really like Kiwame/Koa Speers resistors. These can be found at Mouser under SPR2 and are 40 to 50 cents each, rated at 2 watts which is far above what's actually needed. Not all values are there, so you can get the remainder at a boutique provider like PartsConnexion or just get some Vishay Dales at Mouser. 

Adding the resistors

Then the rest of the parts are added. While Wayne mentioned that the Silmic IIs, which are now being produced in China, aren't as reliable as they used to be, I still like the sound of them so I went ahead and used them. They're over-rated too @ 50V, so hopefully they'll last a while. You'll notice they're a bit large, so some creative mounting is needed. Wayne suggested using Nichicon BPs (bi-polar caps, they're iridescent green) if you'd rather not use Silmics. C1 and C5 are the input coupling caps and should be of high quality as they're directly in the signal path. I personally used some vintage Sprague paper-in-oils, but you can likely fit some of the smaller narrow Mundorf EVO caps or Clarity Caps, either of which can be found at PartsConnexion. The lead spacing is roughly an inch. 

All PCB parts populated

I hate this picture as it looks terrible from all the flux (this is before I cleaned it with some isopropyl alcohol and a toothbrush), but It shows where the film bypass caps are. The units in the audio section are polypropylene and the units in the power supply are polyester. The twisted pair is pulling off the 22V secondary for a pilot light.  

WIMA film bypass caps on bottom of PCB

The chassis I selected is from IAG DIY Tube Audio Products. He lists his chassis on ebay and on his website. Hand-made in the USA and built like a tank. It would be a slightly tight fit so I needed to see where items would be mounted to the front and back of the chassis so they wouldn't bump into any parts on the inside. The IEC filter in particular needed to be offset from the center so it didn't bump into the PCB mounted transformer. I decided to mount the 0.5A fuse and socket on a blank part of the PCB so there'd be one less hole drilled in the chassis. 

Lining up the chassis-mounted parts

Once everything was lined up and the holes cut, the PCB was secured in the enclosure using 1/2" standoffs. The front panel has a four pin connector in addition to a locking Neutrik TRS as most of my headphones are wired that way, so it saves me from having to use an adapter.

Wiring is scraps of Cardas I had in my wire bin, 4x24, 2x24 and 2x21 and some 24AWG, all litz in teflon. The potentiometer is the $40 100K Audionote with solder tags. It's nice and small so I didn't have to worry about it bumping into a discrete opamp. The IEC filter is from Furutech, gold plated. I normally wouldn't spend the money on it but it was discontinued and quite a bargain. RCAs are Cardas rhodium plated. The switch is a simple 3A rated toggle I picked up from Radioshack when they were clearancing everything. The LED pilot light is one from a guitar shop typically used for an effects pedal. Everything else is from the BOM. 

Wiring everything up

Here's a few more images of the chassis with the wood panels.

Front of the WHAMMY amp in the chassis

Back of the WHAMMY amp in the chassis

I used a very simple circuit from ClassicValve for the LED. 

Pilot light circuit to protect LED

Here's an image with the bottom panel and feet installed. 

Bottom panel with vents

...and here's the WHAMMY almost done, just missing the knob. 

Nearly complete

It's quick and easy to swap the op-amp on the unit to slightly alter the sound. Dropping in a Burson Supreme Sound V5 soundeda bit less constricted than the Texas Instruments op-amp that's in the BOM. The difference was less pronounced than if you use a Burson in a DAC, but still an improvement and worth the price of admission (you only need one). I found the V5i picked up a little more noise in this particular amp, so stick with the V5 if you get one. I also swapped in and out the optional capacitors just in case they improved the sound with the Bursons, but wasn't able to hear any difference in any of the configurations. 

Final pics coming soon. 

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. 

The Objective2 (O2) Headphone Amp

People feel so strongly about audio reproduction that it often becomes akin to religion and politics and arguments ensue. Some listeners feel that a perfectly flat response curve and fully diminished THD levels (total harmonic distortion) are the holy grail, while there are others that enjoy the warm distortion and harmonics achieved with old triode technology and a frequency response that tapers the upper and lower extremes. Both are right in their own way, the former looking for perfect accuracy, the latter looking for a relaxing listening experience, and there are probably many listeners that fall in between.

The Objective2 headphone amp falls into the first category, where good measurements are the paramount objective. NwAvGuy has gone to great lengths to provide what many headphone listeners have been pining for, a low-cost headphone amp that achieves great measurements in a vast number of categories. While I don't fall into the category of pursuing perfect measurements (just look at all the number of tubes used in the builds on this site), I highly respect the effort that went into this build and all subsequent documentation.

Something that's quite impressive is that NwAvGuy does not make a penny from these designs. The PCB files are open source and circulated freely; users are encouraged to arrange group-buys on forums such as DIYAudio.com in order to procure the board and/or the front panel. Also, as of this writing, JDSLabs is offering both the O2 board and a unique front panel (to see the JDSLabs CMoyBB being built, please see my previous post). The total cost of the build is very reasonable and should fall under $100 including the case, custom front panel and wall-wart. Add a couple hours of soldering time and you'll have yourself an amp.

The Objective2 Sept 2011 PCB board

What's especially important with closely populated boards is starting with the small parts (resistors and diodes) and working your way up to the larger items such as capacitors and MOSFETs. If one doesn't follow this basic principal, it's much more difficult to fit your fingers into the small recesses between the larger items on the board.

Partially populated, all resistors and small parts in place

The battery clips may look crooked, but they were lined up carefully before soldering to ensure a perfect for for a 9V. This is something one doesn't want to try and adjust later as desoldering them can be difficult. The faceplate shown was procured from a DIYAudio group buy. Many thanks to MrSlim and FlynHawaiian for their efforts.

Fully populated board with faceplate

Faceplate from the DIYAudio group buy

There are a number of testing procedures on NwAvGuy's site to ensure the amp is working properly before you plug a pair of headphones in to ensure that you don't inadvertently damage them with high DC output.

A pair of Tenergy 9V rechargables were dropped in and secured with double sided tape and the unit was boxed up with the case specified by the bill of materials, a Box Enclosures B2-080. Gold was chosen as it's a bit more flashy than a plain black box. Screws were replaced with brass counterparts and the knob was a generic aluminum one from the parts bin, possibly made by Kilo.

Assembled Objective 2 amp

Once the amp had a few minutes to burn in, some cans were plugged in for a listen. All online reviews of this amp were avoided so the initial listening could be done without any pre-conceived notions. The amp reminds me quite a bit of the headphone output of the Benchmark DAC from a HeadFi meet. It's very crisp, clear and has strong, effortless bass. The bass may even be a bit better than the Benchmark was, if memory serves correctly. Both amps are quite analytical; I wouldn't choose them for my own personal musical enjoyment as my ears are sensitive and need the treble and upper-midrange to be a bit rolled off or fatigue sets in too quickly. One can see this amp being highly recommended for audio mastering work as it should convey every detail possible to the editor.

Immediately after building the amp, the input and output jacks were shorting with a variety of different plugs. It appears I received a bad batch as I didn't see any other documentation online regarding issues with the Kycon jacks. Rather than replace them with the identical items, Switchcraft jacks will be wired in as they are very trustworthy. The opamps will also be switched to the low-power versions made by Texas Instruments, which hopefully will be a little bit warmer.

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. 

The Millett Jonokuchi Headphone & Speaker Amplifier

Our industrious friend Pete Millett has released another build of note, the Jonokuchi headphone / speaker amp. The Jonokuchi, like the Engineers Amplifier, makes use of a compliment of very reasonably priced Edcor transformers. Unfortunately, or fortunately depending on your tastes, the Edcor iron is only available with Royal Blue powdercoated bells, so if you'd prefer another color, be prepared to pay for your local shop to sandblast it off or purchase some unpainted bells of the same size.

The Jonokuchi, like the Engineers Amplifier, makes use of old television tubes that are cheap and readily available. It's a single-ended affair that uses 13EM7 tubes with 13V heaters. As stated on Pete's page: the amp design was optimized for headphone use, but still makes a fine amp to drive small speakers to reasonable levels. This is a relatively low cost build at approximately $200 in parts, just add a chassis. Assuming you make use of the PCB, you'll want to go with an 8" x 12" chassis as it should fit everything perfectly. Hammond makes a cheap one for ~$30, or you could get something more exotic like...

... a Hammond Chassis with Walnut Side Panels

...or a custom chassis from ebay seller po1019

Pete also put up plans for a Front Panel Express Chassis that comes with all the holes already trimmed out and labeled, but for nearly $300 for the chassis alone, I think I'll pass ;)

Jonokuchi with custom FPE panels

I was able to pick up my red board just recently from Pete and I've dropped a few parts on it so far.

The lovely red Jonokuchi board

Mostly populated, a few things left to source

I'll update in the coming weeks as the remaining parts arrive. Should be a fun little project. Now which film caps should I use... Obbligato, Mundorf, Sonicraft... oh the possibilities :)


UPDATE (3/05/11): I decided to go with the Hammond Chassis and AmpOhm Paper in Oil caps. Yes... the AmpOhm caps are a bit large, but with some creative mounting, they didn't pose a problem. Pete has the hole layouts in PDF on his website, so download and either print out yourself on a couple pieces of paper and line them up with tape or let Kinkos or Staples handle it on larger format paper. 

Chassis with drilling holes laid out on top

Drilling out the holes on the drill press.

I had Staples print the CAD drawings on the 11x17 paper, but despite saying not to resize in the instructions, they did anyway and I killed the first chassis, so be sure to measure the drawings first no matter what.

Mouting the AmpOhm PIO Caps

UPDATE (4/18/11): I finally finished up drilling the Hammond chassis, there were quite a few holes for tubes, transformers, a pilot light, the IEC inlet and the PCB mounting standoffs.

Front of the Chassis

Rear of the Chassis with oversized holes for Cardas RCAs

Bottom Plate

All holes were drilled with a trusty low-cost drill press and de-burred with a dremel tool. The rectangular opening in the back of the chassis was cut using a dremel metal cutting disc and then filed manually. Once complete, I gave the whole thing a once-over with 180 grit sandpaper.

UPDATE (7/8/11): Finally got the chassis back from my overly busy powder-coater. Now things are finally starting to come together. In place of the 5 watt 220 ohm resistor I placed a Hammond 157J filter choke (205 ohm) that was primed, painted and wrapped with leather. Cardas RCAs were installed on the back panel, along with some nice thick gold-plated binding posts that Parts Connexion was clearancing. I didn't want to splurge on Cardas posts as this amp will likely see a lot more duty as a headphone amp.

Board fitted in the powdercoated chassis

I designed a nice custom plate with the Japanese Kanji from Pete's Front Panel file and copperplate font spelling out "Jonokuchi". These little touches make the amp feel a little more polished and complete. The screws connected to the aluminum standoffs surrounding the tubes were depth-mounted as I'll be placing some decorative metal surrounds around them.

Custom plate embellishes the top of the chassis

UPDATE (8/2/11): The bell-ends are done being powdercoated in lovely a copper color and have been reassembled to the Edcor iron using my typical brass hardware and acorn nuts. I actually take the time to trim down each screw with a rotary tool to ensure that it's the proper length for the acorn. A few extra minutes of effort here and there goes a long way on the finished product.

The transformers were then mounted and the set of copper colored tube surrounds were screwed in place using very short screws as there is very little clearance between the chassis and the board. A jewel pilot light with a 12V LED was mounted on the left and connected to the tube heater pins on one side.

One the Jonokuchi was completely assembled and measurements checked for D.C., the amp was plugged in to verify the LEDs were lighting and the tube heaters were warming up. I then plugged in my trusty Panasonic tester headphones and had a listen. Unfortunately there was a bit of static noise depending on the position of the potentiometer. I ran a connection from the back screw of the Alps Blue Velvet pot to the chassis ground to ensure proper grounding, but that did not solve the issue. In Pete's design, the JP1 connection is used to connect AC ground to signal ground. After shorting JP1 with a short piece of buss wire, the noise was gone.

The amp itsself is on the lively side in my humble opinion, it possessed a detailed sound with taut bass and no rolling off of the high frequencies that I could detect. Unfortunately I was only able to source one pair of 13EM7 tubes (Raytheons), they tend to be a difficult tube type to find in the usual places. I feel that with the right compliment (some warmer tubes), I'll be pretty happy with the Jonokuchi.

UPDATE (8/8/11): I was able to get some custom engraved brass plates for the front of the unit detailing the operation of the push buttons, so those will be the final touch. Here's some final photos:

Jonokuchi Front

Jonokuchi Rear

Jonokuchi Side

Jonokuchi Inside

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.