Crack amplifier

It may not display this or other websites correctly. You should upgrade or use an alternative browser. Thread starter amirm Start date Sep 1, This is a review and detailed measurements of a built Bottlehead Crack Tube headphone amplifier. It was sold from one member to another and kindly sent to me in between for testing.

The original owner did a beautiful job of building this kit:. Joined Jan 7, Messages Likes The panthers seem to be getting more and more unpredictable. Or more predictable? Joined Mar 27, Messages Likes Apart from the bass boost, how else would you describe it affecting the sound of the HD ?

Joined Oct 20, Messages Likes I would love to see the schematic for this amp. Lots of second harmonic Found it! Very interesting. Very low cost construction style. Simple power supply and transformer-less output. I have a lot of NOS twin triodes IBM branded too! Last edited: Sep 1, Click to expand Doodski Master Contributor Forum Donor.

After looking at solid state stuff to look at the bottom of this it is so simple. It's sole purpose in life is to add color to the sound by adding lots of harmonics multitone? The imbalance is tube dependent because of the speedball current source. Should be less in the original version but that one distorts more more 2nd harmonics because of even poorer linearity. 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 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. 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. He says. The manual is very informative and you will actually learn many good practices and procedures by carefully abiding by what it tells you to do.

Make no mistake, the voltages in a tube amp can be dangerous, but the instructions explain fully how to build and test safely. Read carefully. Follow the instructions and warnings. Take your time. Double check everything as you go. Experience is the process of gaining knowledge or skill from doing. Clearly, this is intended to convince you to DIY. The kit is shipped completely unassembled, ensconced in packing peanuts in a small cardboard box. Inside you will find four perfectly cut, unfinished wooden boards and an unfinished metal plate with all the necessary cut-outs for the top.

The wooden bases are made by a local woodworking shop that has been providing them for about 20 years. Being in the pacific northwest, alder is one of the few commercial hardwoods cut locally.

The process of creating the wooden parts is complicated and extensive. It ensures a perfectly cut and finished end product. Fight the urge to just launch right in and start assembly. While you can leave the wood and plate unfinished, the best-looking result will come from properly finishing the surfaces FIRST.

Luckily it will take a few weeks for the kit to arrive after ordering it. This gives you plenty of time to google pictures, and decide what looks best to you.

Does the retro design inspire thoughts of cream and teal antique automotive styling? Perhaps a dark stain and hammered metallic finish to enhance the steampunk sensibilities? Design it to best fit your tastes. Clean the surface of the top aluminum chassis plate and steel end bell with soap and water or isopropyl rubbing alcohol.

Ensure there is no residue left behind to interfere with the paint. The finish on the plate and bell is sufficient for adhesion, so no sanding is required. The manual states that the end bell will rust if not treated with paint or a clear coat. Of note, you can sand the top plate with a random orbital sander and get an interesting brushed finish. I recommend sanding the bottom of the plate after painting to make sure it is clean and ready to act as a ground for the electronics.

Follow the directions on the can, but several light coats and at minimum several days a week or two is better of drying and hardening time pays off dividends. For the kit in the pictures, I had actually painted the top months before starting assembly. Clearly most folks will not want to wait that long, but as much patience as you can muster is recommended.

I recently had the chance to chat with the shop responsible for providing the wooden case parts for Bottlehead. Then flip them over and apply some wood glue to the inside, letting it soak in just a bit before folding it into a box and taping up the last joint. Do this on a flat surface and make sure that it sits as level as possible. Once the glue is dry, I sand off any residue. A sheet of fine sandpaper laid flat I contact cement it to a flat piece of scrap works well.

Plan on doing fine sanding cleanup to ease the sharp edges before any finish goes on. The outsides of the miter corners can be fully closed up by carefully rubbing them on a hard surface to slightly fold over the wood fibers. Allow to dry overnight or as per the glue instructions and make your final finish decision.

When sanding, move upwards through a few sandpaper grits and finish with a grit or there about — for example, in that order.

On a theoretical future build, I plan on using a router to round the top outer edge, while leaving the other edges and corners sharp. I think this will yield a nice finished look. You could just oil the box with Tung oil or seal it with a clear coat and be done with it. Since you are stuck waiting for the paint to cure and dry fully, you might as well take your time and make the box as attractive as you can.

If staining, I would recommend sealing with a Varathane semi-gloss or gloss after a few coats are allowed to dry. Small dents can usually be swollen back up with some warm water and resanded. Alder has complex grain structure that can get blotchy if you go straight to stain. A wash coat followed by very fine grit scuff sanding before adding any color is the usual method.

It definitely creates a more professional looking result. Included in the kit are 4 rubber feet that lift the case. Adding the feet are not optional. Tube rolling is a fun and easy way to tweak the sound to your preferences. I speak from experience here. Try to remember that in general the changes will be fairly subtle and tubes may sound somewhat different but not necessarily better or worse.

Rolling tubes, while having absolutely nothing to do with physically rolling the round tube down a surface, may have been named from the circular rocking motion used to remove a tube from a socket.

There are a huge amount of options of different manufacturers and compatible types of tubes. Sort-of-Drop-In but not equivalent — for best results, replace plate resistors with Speedball boards. So, what are the best sounding tubes in the Crack? There are MANY opinions and long posts out there on just about every audio forum. For power tubes, there is some consensus around the domino plate Tung Sol as being one of the best sounding albeit expensive option. In my opinion, the tall coke bottle shape of the is more interesting looking and distinctive than the shorter round shaped There are just so many possibilities.

Further compounding this, a product like the Garage 6SN7 to 9 pin noval adapter works perfectly to allow the use of 6SN7 equivalent tubes as well in the input socket. Replacing the two output coupling capacitors with higher value capacitors thereby increasing the capacitance can be used to avoid bass roll off for low impedance headphones.

Note that changing the capacitance value impacts the output capacitance and thus bass roll off and higher or lower values may be substituted. Only higher voltage capacitors can be substituted without issue. Unfortunately, affordable large electrolytic capacitors are non-linear with regards to frequency, so are a bit of an audio quality compromise. Suitable film capacitors of appropriate voltage are physically very large think soup can sized and tend to be expensive. In theory, all capacitors used in an audio circuit will have an effect on sound quality.

It stands to reason that capacitors that are directly in the path of the audio signal such as the output capacitors in the Crack have the largest impact on quality. Due to their linear behavior, non-polarized film capacitors are most commonly used in the audio path to minimize any degradation of sound quality. Some modders do change one or more of the three electrolytic capacitors in the power supply with a film equivalent.

Again this becomes an issue of cost and space requirements balanced with any potential benefits. Equivalent series resistance ESR summarizes all the losses due to resistance within the capacitor, including supply, contact, line and most significantly the dielectric losses in the dielectric material. As such, ESR is usually only an important consideration when selecting electrolytic capacitors.

Losses due to ESR will increase high frequency noise, increase ripple, decrease filtering effectiveness, and decrease stability in the circuit. This is another reason to strongly prefer film capacitors in the audio circuit. At the minimum, you are looking for uF capacitance and at least a Volts DC rating stock values. Here are some output capacitor options by no means an exhaustive list, but it does give you a feeling for the range of prices and sizes.

Cans of Coke and condensed soup are included for size comparison. As you can see from my pictures, I decided on the Panasonic capacitors for a couple of reasons.

They are the cheapest option especially with Canadian shipping from digikey. This gained mounting options that most have to forego with the larger cylindrical capacitors. Double-sided tape and a wooden support mounted to the inside of the case work perfectly to hold them securely. I believe the rules regarding diminishing returns apply strongly here. Bypass capacitors are a somewhat controversial inclusion in audio circuits. Whether they improve the audio path, are a potentially expensive placebo, or even a detriment to the sound quality is under some debate.

Much like so much of this hobby. Typically, a bypass capacitor is a small non-polarized film capacitor installed in parallel to another capacitor in the circuit. The theory is basically that larger capacitors are not as good at filling in current spikes and that by paralleling larger and smaller capacitors, it is possible to minimize any unwanted limitations of the capacitor in the circuit. For my build, since bypass capacitors are small in size and relatively inexpensive, I added some utilitarian Panasonic 1 uF capacitors to bypass all the large capacitors in my own Crack.

A common complaint with the inexpensive volume potentiometer included in the Crack kit is that there can be a slight volume mismatch between channels at very low volumes.

I never really noticed this issue, as at any usable listening level for me was above this minimum. However, one of the first upgrades I did in my own build was to replace the volume control. Selecting a new volume control is relatively easy. It must be between 25K and K in impedance — the stock volume control is K. It is wired into the circuit identically to the original volume control.

Speaking from my experience, it looks, feels and sounds exactly like it should. Here again, the sky is just about the limit if you feel like spending money. Stepped attenuators are another higher-level option to put in place of the standard potentiometer volume control. As opposed to a variable resistor as in the case of a potentiometer , attenuators have discrete resistors arranged in a specific number of fixed steps to lower the volume.

Theoretically, this should eliminate channel imbalances, and puts one, or at most a very few high-quality resistors into the audio signal path for the ultimate in fidelity. Supporters of attenuators claim that the sound is more refined, with added resolution and improved high-end clarity. Whether your equipment or your ears are able to discern this level of sophistication is up to the individual. They also tend to be physically much larger than a regular potentiometer, further adding to the real estate problems in a fully modified Crack.

Options include:. I would be remiss not to mention a little-discussed upgrade for all the Bottlehead kits; namely the power cord kit. The cord kit came about after Bottlehead accidentally ordered several thousand feet of gauge stranded wire. They designed a six-foot flexible cord using twisted pairs of wire that are braided together. It is conservatively rated at 3 Amps none of their kits use more than 1.

I recently had a conversation with Adam Goldsmith ohshitgorillas , a headphone and Bottlehead Crack enthusiast, and whose original Crack modification posts inspired my own upgrades and ultimately this article.

He told me the following:.