Introduction to the Beta22
To start with, the Beta22 amplifier is a design by AMB Laboratories. It is a fully discrete, high current, class A headphone amplifier that’s considered by many to be the best of the best in solid state headphone amplification. To quote AMB Labs:
The all-discrete (no integrated circuits), fully complementary and cascoded topology, high-current MOSFET output stage, full class A operation and carefully tuned operating points provide vanishingly low distortion, high speed, wide bandwidth, low output impedance, and high output power. All elements of the design were critically examined to create an amplifier that performs as well on the test bench as it does with music.
The default power supply for the Beta22 amplifier is the Sigma22 which is specially designed to provide high quality, dual rail, regulated power for the Beta22.
σ22 (“sigma 22”) is a high-performance DIY dual-rail, tracking, linear regulated power supply (PSU). Originally designed as a companion PSU for the β22 amplifier, the low-noise, high-current, excellent line/load regulation, wide-bandwidth, and stability characteristics makes it also ideal for other DIY stereo headphone amplifiers, preamplifiers, power amplifiers and other applications requiring a dual-rail regulated PSU.
Since the Beta22 is a do-it-yourself (DIY) amplifier, build quality will vary from amp to amp, and so will the sound properties. Ultimately, the sonic signature of an amplifier depends on the design, and so if you follow the guidelines from AMB, it should be relatively easy to achieve the reference-class sound output. In solid state amplifiers, op-amps and capacitors often provide the biggest tuning capability to the sound. On the Beta22, no op-amps are used (since it is fully discrete), and none of the capacitors are in the signal path, so that takes out a lot of the variables in the sound properties.
The Beta22 is modular, and you can shrink/expand the size of the amplifiers as such:
- Two boards build, sometimes referred to as a “two channels”, is the cheapest and simplest build. It requires two Beta22 amplifier boards (one for each stereo channel), and one Sigma22 power supply board.
- Three boards build is the default configuration. Where in addition to the two boards, another board is added to provide an active ground channel. This requires three Beta22 amplifier boards, and one Sigma22 power supply board.
- Four boards build, often referred to a “Balanced Beta22”, one board for each of the four channels in a balanced stereo configuration (L non-inverting, L inverting, R non-inverting, R inverting). The four boards build can be powered with a single Sigma 22 power supply, or dual Sigma22 power supply to have a dedicated power supply for each stereo channel. The four boards can also be wired for handling a regular unbalanced headphone, in which only two boards will be used.
- Five boards build gives the benefit of having a four boards for balanced operation, as well as a three boards configuration for an unbalanced operation with active ground. (The active ground board requires a different configuration, hence you can’t have active ground in a four board build)
- Six boards build gives the benefit of having four boards for balanced operation, as well as two sets of single ended amplifier outputs with active ground on both.
Clearly, the number of boards will add to the total cost and complexity of the project.