Clive wrote:
> In message <h2lj51$8ud$2@news.albasani.net>, The Natural Philosopher
> <tnp@invalid.invalid> writes
>> I always felt the quad valves were good, but neither the 303 nor the
>> 405 were in any way special: Certainly I was able to beat them with my
>> own designs.
> H.W.Hellier wrote about the designs and the Quad triples, I seem to
> remember that these were more glowing than the later "feed forward" 405.
> When ever has there been a good Hi-Fi amp without a lot of feedback and
> a virtual earth point?

My own experience was that in chasing paper specs, a lot of relevant
stuff got missed. By far and a way the largest issue with a transistor
amp is the crossover distortion in a typical class B or AB style design.
Unlike calves, this gets much worse at low levels..but due to the way
valves work, it was usual to measure distortion at high power. And IKhz.

Whereas using a small 10KHz signal could often show ghastly distortion
of several percent..

The key is to use modified class AB with bipolars, and run in class A
for small signals, and also to try never to actually switch one side
OFF, as that led to issues with time delay switching it back on: A nasty
problem of thermal stability was then encountered.

The adoption of power FETS with much better frequency responses,
negative temperature coefficients and low switch on delays made that
almost a non problem.

Everyone used feedforward at some point to sharpen up transient
response, and compensate for overall lag. .