[Ardour-Users] New tube amps

David Kastrup dak at gnu.org
Tue Dec 26 04:07:20 PST 2017

Will J Godfrey <WillGodfrey at musically.me.uk> writes:

> First, let's be clear. I am not suggesting a valve amp can't be emulated, but
> your drawing is, to put it mildly, 'basic'.
> A friend of mine retired recently (well into his 70s) from a company
> that does indeed make amps with extremely good emulation, and if it's
> good enough for him, having cut his teeth on valve stuff, it's
> certainly good enough for me - a mere refugee from the valve TV days.


> Your drawing looks similar to one I've heard in operation, and where it failed
> was on long slowly decaying single notes. As the volume dropped you could
> clearly hear the steps in the harmonic content change. This of course doesn't
> happen in a real amp where the non-linearity is a continuous sweep until actual
> hard limiting is reached (quite difficult to get to).


> You'll get even better results using an FET, but by then you might as well use
> a JFET wired in a similar way to a triode! Wire two in cascode configuration
> and you'll get somewhere near pentode behaviour.
> Talking about pentodes, why on earth emulate an EF86? They were
> horrible valves. Fragile, microphonic and frequently suffering from
> heater-cathode leakage - everything you *don't* want in an AC heated
> input valve... in kit that's going to be rattling around in the back
> of an old Bedford van. The only ones I saw were in amps people were
> desperately trying to get rid of!
> Back to subject, your drawing seems to try to combine the features of
> the input stage (creating mostly even order distortion) with the
> output stage (mostly odd order). This takes away control from the
> guitarist who may want to overdrive the input for consonant harmonics
> with just a little compresssion, then with a quick flick of the wrist
> change to clean input and heavy overdrive of the output.
> Added to this your need for EQ, if it was adequate to tame the sound
> for open strings, would completely flatten the 'edge' when working
> high up the fretboard. Watch the best Rock guitarists. They are all
> over the fretboard!

I think we are getting back to a point seminal to instrument design: the
imperfections one had to live with in the past were used to carve out
musically useful compromises with a broad brush.

The resulting systems were hands-on and coherent.  Current technology
does not have the coarse elements of the past and can present anything.
But to many the ultimate challenge seems to be modelling the past's
deficiencies as well as possible since that lends the illusion of being
hands-on and coherent, in reality being arbitrary within the constraints
of the modern components.

David Kastrup

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