Class-A Buffer

Class-A Buffer

Drag Control

Tonebone Classic
StageBug™ SB-15 Development

Over the years, Radial has gained tremendous accolades for the sound of our signal buffers. Buffers are most often unity gain amplification circuits that enable the circuit designer to manage the signal and make it do something. That 'something' could be the input section of a distortion pedal, a phase shifter or simply drive the input to a tuner.

As with anything… not all buffers are created equal. In fact, buffers – or shall we say – less than ideal buffers, are the primary reason that more discerning guitar players prefer 'true-bypass' pedals and hate the sound of wireless systems. So why do guitarists hate the sound of buffers? It actually has to do with several factors including the type of circuit being used, the part selection, how the circuit loads down the pickup and noise.

Circuit types

Ask any audiophile and they will tell you that class-A circuits sound the best. The reason for this is actually quite simple. Class-A circuits use a single gain stage to amplify both the positive and negative side of the wave. The problem with class-A circuits is that they are very inefficient. This makes them a terrible choice for integrated circuits or ICs that pack thousands of transistors into a small, highly efficient and low cost chip. Guitarists don't give a hoot about saving calories… they want tone.

Part Selection

Chips or ICs are amazing! They generate tons of positive gain in a very small package… in fact so much gain that they require huge amounts of negative feedback to keep them in check and make them controllable. For cell phones, TV sets and car radios, they are great! But for toniacs… the massive amounts of negative feedback makes the guitar sound thin and electronic. By employing discrete transistors at each stage, we can eliminate most of the negative feedback and it ends up sounding more natural.

Loading the pickup

Blame it on Leo Fender! Over the years, we have come to realize that solid state circuits react differently than tube circuits. When Leo launched his first tube amps, he chose 1 meg-ohm as the perfect load for his Fender Telecaster. So the world followed. Way back in 2001, we realised that the solid-state front end actually sounds and feels more tube-like when you lower the impedance to 220k-Ohms. This led us to develop Drag™ Control – a simple circuit that lets you adjust the load to suit your playing style and setup.

Noise management

There is no substitute for experience. Our team of engineers each have over 40 years of experience in circuit design. This means that they do not 'guess' as to what signal trace should go where and what part may induce noise into the next, they know. This knowledge results in lower noise and greater longevity without failure. There are more expensive products out there… but very few are better.

These are the components that make up a great sounding buffer.

The Tonebone Connection

Over the years, we have received many requests to make our big Tonebone pedals work with 9V power bricks. Although 9 volts is plenty for average pedals, the higher voltage (15V) and double the average current (400 milliamps) increases the headroom and dynamic range.

So instead of reducing the quality… we have come up with a cool solution… take two 9V outputs from a power brick and combine them to deliver the 15 volts!

Integrated circuits versus discrete electronics

The easy way to design a booster is to employ integrated circuits or ICs. The marvelous technical wonders pack hundreds or even millions of transistors into a very small space to generate huge gain. Once the gain has been produced, negative feedback is sent back into the audio stream to control the gain so that the amplifier does not run away. Mix negative gain with a positive signal and something has to give – phase cancellation! This is why most 'purists' hate the sound of solid-state amplifiers. The Elevator employs individual transistors for each gain stage so that negative feedback is minimized. The result is a much more natural sounding signal path.

Class-A versus Class-AB amplification

Early amplifiers were class-A, meaning that they employed a single gain producing devices such as a tube or transistor to amplify the full audio wave. The problem with class-A circuits is that they never shut off and are not very efficient. Class-AB amplifiers were developed to solve these problems by breaking the wave into two parts – positive and negative (push – pull) where each half of the wave is amplified individually. After the signal is amplified, the two half waves are brought back together to produce the final output. The problem of course is bringing the two half waves back together in perfect alignment. As this is practically impossible, zero-cross distortion in introduced causing the harshness that folks do not enjoy.

Integrated Circuits
Integrated circuits contain hundreds of transistors in a super compact package.
Discrete Components
Individual transistors allow precise control of the gain at every stage.
Negative Feedback
The signal is first amplified and a portion is sent back as negative feedback (R2). Less negative feedback sounds better.
Class-A Buffer
The simplicity of a class-A circuit with a single-ended design is free from zero-cross distortion.
Class-AB Buffer
Class-AB circuits break the wave in two components and then bring them back together.