Why use an output capacitor at all – why not incorporate a servo, etc., as found in some competing designs?
Balanced Audio Technology has built its reputation for superior sound largely due to its trademark use of very short signal paths, with only a single gain stage used in its preamplifiers. Any single gain stage known to man today will shift the DC level of the signal. A typical gain stage will introduce anywhere from 10V to maybe 400V as the output DC component (depending upon its technology – tubes or transistors). Op Amp circuits can ostensibly get around this by being internally composed of three or more gain stages as well as relying upon a tremendous amount of negative feedback. This type of penalty is unfortunately typical when trying to “defeat” the DC component in the output signal without the use of output coupling capacitors or transformers. In order to remove the DC component resulting from the normal operation of a tube amplification stage, at least one additional gain stage (often a cathode follower) must be used, in conjunction with some type of DC servo circuit. Needless
