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In Reply to: How has solid state advanced in the last 20 years ? posted by PeteL2 on June 3, 2001 at 09:39:00:
[soapbox]Although there have indeed been incremental advances in both the devices and the implementation of the devices, there still remain fundamental issues that are not adddressed by the vast majority of designs.
[/soapbox]
I would hazard a guess that the biggest [ but not the only ] differentiating factor between solid state and vacuum tubes relating to sound quality is not an electrical characteristic, but a *thermal* characteristic that influences electrical parameters.
Other fundamental characteristics give vacuum tubes the edge [ pun time ] : a vacuum is as close to textbook perfect as we can get for a dielectric so device stray capacitance has less of an influence on the sound quality, and electron [ not current ] density is not impeded by a minority carrier junction.
In typical implementations, thermal self induced parametric shifts
[ "thermal tails" ] are orders of magnitude worse for solid state circuits than vacuum tube ones. The knowledge of thermal tails is not particularly new, but the vast majority of circuits show no signs of having been designed with that awareness.Unless specifically designed [ or accidently put ] in constant power mode, any device will shift it's characteristics with a time smeared envelope of the music signal as it heats up and cools down. Sharing substrates [ as in monolithic integrated circuits ] further complicates the equation, with different devices no longer being individuals, and each one heating up the others with varying thermal time constants. Adding loop feedback makes things worse, as the input differential pair is unable to function as a true difference stage when perturbed thermally by the mishmosh of thermal fronts on the substrate. Of course, put a steady state signal through and all looks well.
Hope this is not taken as a troll, but I think we have a way to go in implementing what we already know about the devices available. Tubes just happen to have characteristics that lend them to more musical, enjoyable sounding designs. Don't tell anybody, but there are solid state devices in one of my systems, just no opamps.
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- It's getting better...no your not, you'll be stone cold dead in a bit - wildmonkeysects 17:08:35 06/05/01 (0)
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