Among seemingly a million other projects, I have been developing a new flagship amplifier, using a newly developed topology (for lack of a better word, it pains me slightly to use it as it is so thrown about these days - but I think this just about qualifies)

The first amplifiers to use this "topology" will be 100W KT88 or compatible monoblocs. Somewhat like Radford's own ISA series of amplifiers that were conceptualised but sadly never materialised, the aim is to achieve a genuine step up in performance in valve based amplifiers which I believe I have achieved with this design, and a working proof of concept exists.

The design is inspired by Radford's own TT100 amplifier, in that it is a hybrid design. The output stage is of course valve, but driven via a highly linear differential Class-A transistor stage. The actual amplifier circuit is extremely simple, but afforded very high performance thanks to other innovations, and perhaps to the simplicity itself.

The basic thinking behind this new design is to eliminate or significantly reduce some of the misbehaviours the vast majority of valve amplifiers exhibit - ones that cannot possibly be argued to contribute a pleasant coloration. In doing so, both the subjective and measured performance significantly improves, and the benefits can clearly be demonstrated.

Chasing low distortion was not the goal, but measurements taken from the prototype amplifier, show THD on the onset of clipping at 1Khz, as low as 0.03%. Distortion reduces further with level and at typical listening levels, practically nonexistent. No extreme measures were taken to lower the THD, but this improved linearity is a natural result of removing sources of "misbehaviour" elsewhere in the amplifier.

THD at full power at 10Khz is still as low as 0.2%, which for a Class-AB amplifier using a single pair of output valves, is remarkably low.

This new amplifier will feature a few innovations such as fully automatic biasing (not a new concept in itself), using simple analogue circuitry to set the true quiescent point of the amplifier at all times. This affords a useful advantage in that valve matching becomes far less important for good performance, and eliminates all biasing worries - the bias will be set to a higher degree of precision than is strictly needed, at all times.

There are more innovations to list, so more details, including prototype pictures, to come soon!!