First up, I am selling my beloved Bottlehead SEX amp. This is the 3.0 version with C4S upgrade. No unofficial modifications were made, and original tubes are included as well as brand new spares from The Tube Store. I'll also include a power cable I made for it. The unit is fully assembled and in great condition.
Editor’s note: In this article, you will learn to BUILD the Bottlehead Crack. If you are interested in UPGRADING the Crack,.Originally announced in 2010, the Crack is an affordable tube-based headphone amplifier kit offered by the located in Poulsbo, Washington State, USA. The company was created by the ‘President for Life’ Dan ‘Doc B’ Schmalle in the mid-1990s, and primarily offers DIY tube audio kits for both headphones and home stereos.The is Bottlehead’s biggest selling kit and has earned a reputation as a fun and easy-to-build project. Yet it yields an amplifier whose performance punches well about its price point. These are impressive results for an amplifier that Doc B originally: “ was done partly as an exercise to see just how quickly and efficiently we could get a project from the hand waving phase to the production prototype phase.” The finished product.Bottlehead considers the Crack a simple circuit “ Skill Level 1” kit.
This makes it first-time builder friendly. It has a low parts count which keeps the price reasonable.
It’s on its second revision (version 1.1) since release and can typically be completed in 5-10 hours depending on expertise and level of care.One of the best things about a Bottlehead kit is the instruction manual. It is chock full of friendly hand-holding steps and pictures.
It includes information on how to solder components for beginners and troubleshooting steps if things don’t go as planned. Coupled with the excellent community found on – where all questions you have will be (or already are) answered. – the support is outstanding. This takes a lot of the fear out of tackling a DIY product.Tyll Hertsens, the former writer for Inner Fidelity. “the Bottlehead Crack is a superb introduction into the world of DIY audio.
The parts quality is very good, the documentation is truly excellent, the Bottlehead forums provide fantastic peer-to-peer assistance, and construction is very easy. The Bottlehead Crack is an outstanding first project for the novice audio DIYer. The big win, however, is that once you’ve finished your build, you’ll have a fantastic sounding for your high impedance headphones.
I simply can’t recommend the Bottlehead Crack highly enough, if you’ve got a yen to try a little soldering, this is the way to go. You’ll love it!”. Building a Bottlehead CrackLater on, I’ll caution you of some serious limitations of the design of the Crack, while hopefully conveying just how good this kit can sound (if paired properly!).
But first, let’s take a look at building one. I’ve been through the process a few times, so I should have some tips and tricks you will find handy. All the parts organized.Please note that Bottlehead is rightfully protective of their intellectual property. The excellent and detailed instruction manual is what keeps a frugal DIYer from simply sourcing most of these readily available parts themselves (beyond a few kit specific parts such as the power transformer). The manual is available as a single time download upon purchase of a kit, and as such will not be shared here.
I will try to walk the line between providing detailed information with good pictures, and not sharing too many specifics.I’ve owned a version 1.0 Bottlehead Crack for a few years now. It sounds so good, that I’m happily limiting my headphone choices and I’m in no way looking to replace it.
In this crazy hobby of upgrade-itis, that’s saying something significant.I love DIY, and recently when a friend mentioned they were interested in the Crack, but lacking the skills and tools to build it, I happily volunteered. So what follows is tips from the building of their Crack version 1.1. Knowing it was going to be documented, and since it is for a friend, I completed it in a rather neater manner than my own.
Necessary ToolsBottlehead’s Doc B recommends getting a decent digital multimeter (DMM) first. “that will be your primary test gear 98% of the time”. Rather than buying an expensive DMM, such as a Fluke, buy a basic one rated minimally for 500VDC and “if you want to spend on something fancy, put your money into a good solder station A good moderately priced station like a Hakko will make soldering so much easier that you will need test gear to sort out your messups far less often. Good wire strippers are another must have. I like the Ideal type, but whatever works well for you is the thing to use. “A good solder joint should encapsulate the terminal (or solder pad) and all the wires connected to the terminal. This begins with a firm mechanical connection between the wire and the terminal.
The solder should be shiny in appearance and it should have flowed into the joint well enough to create fillets in the ‘corners’ where the wire and terminal meet.”There’s a lot more detail in the manual. You should read it! Input WiringRCA input wires are braided to resist noise (it doesn’t require shielded wire) and are attached to the volume potentiometer. From there to the small input tube socket and onwards to the headphone socket. The delicate LEDs on the input socket.Bottlehead uses LEDs to set the bias for the input tube to 1.56 volts.
The used is unfortunately fragile with very thin legs, but it has a low effective resistance and is electrically quiet, making it an excellent choice. Soldering the LED is the first tricky part of a basic Crack build. Ensure the correct orientation, cautiously curve the legs to allow for the flexing of the tube pin sockets when tubes are inserted and removed, and carefully solder in place. The addition of a couple of resistors rounds out the input wiring. The Power SupplyNext up is the high voltage power supply. In my opinion, orienting and soldering the 4 diodes in the power supply is the least enjoyable and most fussy part of the build. Especially if you are trying to do it neatly with nicely squared off bends.
Those pesky diodes.Note that wire lengths, component spacing, and component orientation matter and making a mistake here can irreparably damage the power transformer. An expensive ($100 + shipping) punishment for not being careful.On the topic of neatness, I eyeball the appropriate length and use the needle nose pliers to bend 90-degree angles in the component leads wherever possible. It looks so much tidier, but it isn’t necessary to do so.Remember that those rectangular sand block resistors in the kit are big and beefy because they get HOT. Ensure when you install them to give space around other components wherever possible. Sand block resistors in the power supply.A note about the capacitors and diodes in the kit. They must be installed with the correct polarity.
Polarity is marked with bands physically on the component. Follow the directions carefully and triple check. Things will catastrophically fail if installed in the wrong orientation. Output WiringThis is the final stage of the basic Crack build. Add a couple more capacitors (note orientation!) and a couple of resistors on the headphone jack.
Power tube socket and output capacitors.There is a simple fix if you find the Crack is too loud and you would prefer more usable range in the volume potentiometer (this also solves any channel imbalance at low volumes). Add a couple of 75K resistors (1/10 Watt or greater) where the red and white wires connect to the volume pot and a 33K resistor between each of the outer pair of lugs on each level of the volume pot and ground lugs on the pot. Nice and tidy. Testing and ListeningThat’s it. Soldering is done.NOW DOUBLE CHECK ALL YOUR CONNECTIONS TO MAKE SURE YOU DIDN’T MISS ANYTHING! CHECK THOSE CAPACITORS AND DIODES AGAIN!You will do a resistance check and if passed, a voltage check before plugging in a source and headphones.
Once everything tests in the correct range, I recommend finding a pair of inexpensive (and sacrificial headphones) for the first listen. Better safe than sorry.
If everything still goes well, grab your favorite high impedance headphones and give it a real listen. Listening for the first time. The Crack is known to be very quiet with little to no audible hiss, but with nothing playing “there will likely be some noise with the volume control at its maximum level. The amount of noise will depend greatly on the impedance of the headphones, but the important thing to remember is that this is well beyond a comfortable listening level.” –If you run into any odd issues, check all your connections for the umpteenth time, follow the troubleshooting steps in the manual, or if all else fails, join those asking for help in the forums.Why Doesn’t Everyone Own One?In very many cases, the performance of a Crack is very favorably compared to amplifiers costing much more. It is almost universally hailed as the affordable end game option when paired with the timeless or ’s.It offers top tier sound at a mid-tier price – especially with the release of the $200 (identical to the HD650 at a much lower price point).
A Controversial Design Everything is located on the top plate.The design of the Crack delivers both its principal strengths and weaknesses. The Bottlehead aesthetic tends to be a polarizing one.
Atypically, all components, controls and inputs/outputs are on the top plate which sits unattached on a plain wooden case. This simplifies the design, makes it easier to work on and lowers the price, but creates a retro-utilitarian look that you either embrace or not.Aesthetics aside, the critical thing to understand about the Crack before purchasing, is that it is an. OTL AmplifiersThe OTL design seriously LIMITS the variety of headphones it is compatible with. Really there are only a few that will work and sound proper powered by a Crack. However, those that do, sound wonderful.The Crack will not work well with most headphones. I want to make this absolutely clear.
The Crack is extremely picky with headphone pairing.The Crack has no output transformers and as a result of its particular design, it has a high (120 Ohm). Output transformers in tube amplifier designs are typically used to lower the amplifier’s output impedance and to make them more universally compatible with many headphones. Benefits of OTL AmplifiersTube amplifiers with output transformers are typically preferred due to the flexibility of headphone pairing options for the owner, however the OTL design has a few significant benefits.Output transformers are large, heavy, and difficult to manufacture. This results in significant cost savings if there are no output transformers in the design. Additionally, output transformers can be a major source of distortion, so higher sound quality can (theoretically) be achieved with a properly designed OTL amplifier.
OTL Amplifiers are Current Limited but High VoltageWhile it can provide high voltage, the combination of the Crack’s high output impedance and the headphone impedance limits the amount of current it can provide. This creates a couple of compromises:1. Will it work well with,?No. The Crack is not suitable for headphones which require a lot of current. Look elsewhere for an amplifier if you own this type of headphone.
“Ohm’s law tells us that Power=(Current 2).Resistance. When resistance goes down, power also goes down. While this may not be that big of a deal for a sensitive headphone that is low impedance, it is a big problem for power-hungry headphones that are also low impedance.” –2.
The Crack is only suited for high impedance headphones that require (or benefit from) a lot of voltage.The rather unique specifications of and Beyerdynamic headphones are why they are frequently mentioned when discussing the Crack.For instance, the HD6xx line can require high voltage (3-6V) at around 100Hz, making it a poor pairing for many lower powered mobile devices, but an ideal match for the Crack’s characteristics. Low Impedance Headphones will Suffer from Distortion and Bass Rolloff.