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 from another. In crowded circuit boards, signal paths often run in parallel causing interference and this can be avoided to some extend with solid core wiring. The obvious disadvantage of course, is that even simple circuits take up much more space.
Bottlehead Crack overview:
- Part 1: Cabinet and chassis
- Part 2: Mounting the parts
- Part 3: Soldering the components
- Part 4: Speedball Upgrade
- Part 5: Hot Rodding with film caps
Time to install the different components and solid core wires.
You can bend the solid core wiring and they’ll stay in place. They are of the Coral brand and made in USA. Notice that the signal from RCA to potentiometer needs to be braided. The power lines from the transformer to the two tube sockets are twisted.
The tiny LED’s going from the center terminal of the nine pen socket to A3 and A8 are a bitch to fit and solder, so you better be prepared for that. Plate load resistors are installed above the tube socket.
The power transformer is rigged up and soon we have a genuine power supply going. Rectifiers are used to make a full wave bridge
Resistors soldered directly to the headphone jack. From ring terminal to each channel.
Power supply filter capacitors (220uf 250v) are attached. The final capacitor is fitted with a 270k ohm 1w resistor. A 270 ohm 5w ceramic resistor is attached from one capacitor to another.
Output stage cathode resistors. There are joined and soldered before being mounted. Notice the vent above the resistors, they get really hot and need somewhere to dispose of the heat.
Almost complete. We need the output capacitors and the wires connecting them to the tubes.
Output capacitors installed and ready.
First the resistors are checked with a cheap, but pretty good voltmeter. Then all the voltages are checked with the power jacked in. This is dangerous stuff, so be aware of the hazards. The 270K ohm resistor between the last filter capacitor caused some problems and I had to find a replacement. I contacted Bottlehead about it, but they didn’t respond to my email.
It’s done. How does it sound? Pretty awesome and definitely a little better and more dynamic than my O2 amp. It has a bigger bottom while retaining all the details. But it hasn’t got a completely silent background above 40% volume or so.
I am very satisfied with the looks of the amplifier. I can honestly say it’s the most beautiful piece of audio equipment I have ever owned. I am proud that I actually made this I have the Speedball kit waiting to be installed and I can’t wait to hear the difference, I expect it to be huge.
Go to part III here: Speedball Upgrade