In rec.photo.digital.slr-systems Alan Browne <
alan....@freelunchvideotron.ca> wrote:
> On 2013.05.07 16:25 , Me wrote:
>> On 8/05/2013 1:02 a.m., R. Mark Clayton wrote:
>>>
>>> There might be a bit of nostalgia for vinyl records and even some
>>> misplaces
>>> preference for valve amps, but I doubt many other than Kodak will
>>> mourn the
>>> passing of wet film.
>>>
>> Some of the preference for valve amps isn't misplaced. They're still
>> the standard for some instrument amplification (guitars).
>> There's also a parallel there with film/digital photography, as digital
>> sond processing is used in sound-processing in so-called "modelling
>> amps" (solid state) to replicate the "tone" (non-linear response) of
>> valve amps. It's a bit like using a "velvia" filter in photoshop etc,
>> to replicate the look of film.
> The sole advantage tube amps have over transistors is the continuous
> smooth transition of -ve to +ve voltages through the signal range
> whereas transistors have a discontinuity near 0 volts (for both the
> "push" transistor (+ve side) and "pull" (-ve side) of the output in a
> class B amplifier).
That's not an inherent charcteristic difference between transistor and
tube amps, it's simply a difference in the way te amplifier is
designed, e.g. class A, B, etc.. Neither device inherently can make
the +ve to -ve transistion. Tube amps managed it by simply biassing
themselves high so that the zero signal point was handled half way up
its voltage range. In the earky days of transistor amps the devices
didn't have the power to do that, so they chose to switch between
devices, one handling the +ve side, the other the -ve.
But teansistors are now powerful enough to run in the smae mode as
tube amps, i.e. with the zero signal point biassed half way up their
voltage range. And for those who care there are transistor amps made
to that design.
> That discontinuity in transistor based circuits
or tube amps operating the same mode.
> is audible to about
> 1/1000th of a percent of listeners. IOW, even "audiophiles" <cough>
> with the best trained ears would fail to pick it out in an ABX test.
> Anything related to the "tone" can be done in analog or digital circuits
> - more so in processing.
There were more differences than that. When tube amps were pushed past
their limits the distortion started rising, but it did so gracefully
and slowly. Whereas transistor amps pushed past their limits move very
rapidly into higher levels of distortion, and also a kind of
distortion which has a harsher sound. Since the loudest music tends to
be when lots of instruments (or voices) are playing at once, this
difference was most obvious as a muddying of clarity in loud
orchestral or large choir passages. Those with keen ears could also
pick up it with instruments which had very large sharp transient peaks
in the attack of their notes, such as a piano.
--
Chris Malcolm