Well, we certainly seem to have struck a chord with the publication of the Mudlark valve amplifier design in the preceding two issues, August and September. We have had some very enthusiastic letters from readers. At one level, I can understand the enthusiasm. With their glowing valves and the heat rising from them, valve amplifiers can seem almost animate, in much the same way as a steam locomotive at rest can seem almost "alive".

But on a pure performance level, I really cannot understand the attraction. Many people claim to love the sound of valve amplifiers, citing their "soft" overload and tendency to produce low-order harmonic distortion instead of the "highly undesirable high order" harmonic distortion of modern solid-state amplifiers. Now it is one thing for a musician to prefer a valve amplifier because of the particular sound it can be made to produce when playing a guitar. It is quite another for someone listening to CDs to prefer the sound of a valve amplifier over modern solid-state hifi designs which DON’T suffer at all from high-order harmonic distortion.

Unfortunately, there is lot of myth-making out there in the hifi market-place and too many people just swallow it. For example, among some valve enthusiasts, single-ended amplifiers such as the Mudlark are much preferred over far superior class-AB push-pull valve designs. Partly, this is because single-ended valve designs have predominantly second harmonic distortion which is preferable to higher order harmonics. But what people do not realise is that these single-ended amplifiers have LOTS of second-harmonic distortion.

Furthermore, if you have high harmonic distortion in a circuit, you will ALWAYS have high intermodulation distortion. This is never mentioned when you hear people waxing lyrical about valve amplifiers. Intermodulation is the product of two different tones fed to a system – sum and difference frequencies are the result and these are never harmonically related to the input tones. On complex orchestral and choral music, high intermodulation sounds horrible.

Interestingly, before the advent of solid-state amplifiers, high quality push-pull valve amplifiers were the order of the day – single-ended designs were regarded with disdain.

But forgetting distortion – and many valve amplifier enthusiasts seem happy to do this – there is a huge amount of nonsense being circulated about valve amplifiers. For example, printed circuit boards are regarded (by some self-appointed gurus) as undesirable because they can lead to earth loops while supposedly, such problems do not exist in amplifiers with point-to-point wiring! In fact, some amplifiers are assembled with silver wiring because this supposedly minimises earth loop problems. What utter drivel!

By all means, build and listen to valve amplifiers if that is what you enjoy. They do sound quite different to the best solid-state amplifiers. They can even sound very pleasant. But to genuinely believe that typical valve amplifiers with low orders of feedback are more "hifi" and sound better than the best solid-state amplifiers is merely self delusion.

Leo Simpson