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Re: Sound of tube amplifiers

Dear Linda + list,

One likely physical explanation for the "warmer" tube sound, is the type
of non-linearity in tube amplifiers compared to solid-state amplifiers.

The static input/output curves of tube amplifiers are asymmetrical,
causing distortion products that are even harmonic (2nd, 4th etc..).
These even harmonics are musically pleasant to the ear as they are in
familiar intervals (2nd harmonic = 1 octave etc..).  Furthermore, the
tube amplifiers tend to saturate in a nicer way at high levels, known as
"soft" clipping.

Transistor amplifiers, on the other hand, produce symmetric artifacts,
both at zero-crossing and at clipping.  The harmonic distortion is
dominated by odd harmonics (3rd, 5th etc..), which are not like any
musical interval.  This is believed to cause the "cold" sound.  At high
levels, the amplifier will hit the power supply rails very suddenly,
causing "hard" symmetrical clipping and eventually turn a sine wave into
a square wave.

Hope this qualitative info helps..

Lars Bramsl°w
Bruel & Kjaer
Skodsborgvej 307
DK-2850 NŠrum

Tel (front desk):       +45 45 80 05 00 
Tel (direct):   +45 45 80 78 55 (tone) 2663
fax:                    +45 45 80 40 82

email:                  mailto:lbramslow@bk.dk
web:                    http://www.bk.dk

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