Aikido octal mono PCBs and 5687 PCBs and Aikido and 300B amplifiers

Posted on Feb 7, 2014

Buffers belong in a subset of amplifiers, in general. In addition, power buffers can be thought of as belonging to a subset of power amplifiers, in specific. (Isn`t taxonomy fun ) The uniting features for all buffers are unity gain and a low impedance output (and, we would hope, low distortion). When we look for commercially made buffers, however, we see that a third feature has

Aikido octal mono PCBs and 5687 PCBs and Aikido and 300B amplifiers
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been wedged into the feature list ”namely, wide bandwidth. Yet for our ear-restricted purposes, bandwidth to 100 kHz is more than enough. (In fact, many great sounding tube amplifiers have a power bandwidth that only extends up to 40 kHz. ) A common, but not universal, additional feature that many buffers share is that they are feedback free well, at least, global feedback loop free. (Since the buffer is often used to replace the power output stage of an amplifier ”say a low-noise amplifier that cannot on its own drive low impedance loads ”feedback-free allows more latitude in wrapping one global feedback loop around both the voltage amplifier and the power buffer. ) For our purposes, namely, using a solid-state power buffer after a vacuum tube voltage amplifier, low distortion is primary; with low-output impedance and freedom from feedback coming second and third. However, a low distortion buffer comes at a price: high idle current. Ideally, our buffers should only be run under class-A operation. Push-pull class-A output stages are naturally clean, as sharp on-off transitions are excluded and the two output devices` transfer curves combine in single flatter curve; additionally, class-A operation prevents the problems of switching distortion, gm doubling, and tweaky bias adjustments. Class-A operation, however, is far from efficient. In spite of what the glossy ads say, class-A is brutal, requiring a heavy current draw and...

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