Category Archives: Bottlehead Crack OTL

Stepped Attenuator & legendary G.E.C CV 2523 tube

The stepped Attenuator is an alternative to the usual potentiometer controlling the volume. The difference is that the potentiometer uses a track of a resistive material like carbon or plastic, where a stepped attenuator uses a mechanical switch combined with traditional resistors.  A metal film transistor should be less noisy than the resistive material in a potentiometer and hence the improvement sound quality. The other benefit is that the balance between the channels should be absolutely perfect. That’s the theory at least.   There are different types of stepped attenuators…

Bottlehead Crack and Speedball review

The Bottlehead Crack OTL tube amplifier is widely praised  for it’s smooth, but neutral and detailed sound. If you own a pair of Sennheiser HD600, HD650 or even the HD800 flagship model, this is what many will recommend you to buy. This is especially true if you ask the question on the Head-Fi forums. Coming from the very neutral and lovely Objective2 amplifier, I wished for something more dynamic, more alive, simply with more feelings to the sound. Don’t get me wrong, I love the O2 and ODAC combo more than…

Speedball Upgrade

When I ordered my Bottlehead Crack kit, I also ordered the Speedball upgrade right away. Everybody that tried it, including reviews, said it was a night and day difference from the default Crack setup, and that you basically had to upgrade it. So of course I wanted to hear that for myself. Bottlehead recommends building the default Crack and make sure it works properly before moving on to the Speedball upgrade, so this is why I have done so.

Soldering the components

The Bottlehead Crack is not made on a printed circuit board like modern amplifiers. Instead all the parts are mounted and soldered on terminal strips and connected with solid core wires between the components. If done properly with good soldering skills and quality wires, this is a very good way of making circuits for amplifiers. It’s also a way of using three dimensions, instead of the two dimensions you are often restricted to with circuit boards. Another obvious advantage is more space between components, wires and interconnects, causing less interference…

Mounting the parts

This is the second part of the Bottlehead Crack build. It’s time to place all the parts on the freshly painted chassis and prepare for the final assembly of the amplifier. This part is just the preparation of the chassis before soldering the part on the terminals,tube sockets and power transformer. From here on, it’s all about the circuits and electronics.

Cabinet and chassis

This is the first part of the Bottlehead Crack build. In the following parts I will show how I made my Bottlehead Crack amplifier and maybe even give you some inspiration for your own DIY projects. Bottlehead Crack is an OTL tube amplifier for high impedance headphones. OTL means that it’s an Output Transformer less design. The output transformer in a tube amplifier causes a lot of distortion because it’s located directly in the signal path.