Manley TNT MICROPHONE PREAMPLIFIER - Manual (Page 20)

Audio Precision 06/26/06 18:06:03
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Audio Precision 06/26/06 17:55:11
FFT SPECTRUM of THD Residual @ 1kHz
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TUBE CHANNEL DISTORTION FFT
TUBE CHANNEL DRIVEN JUST 2 dB HOTTER
The TOP graph shows the distortion harmonics just prior to full clipping.
Notice both even and odd harmonics and a smooth decay of upper harmonics.
The BOTTOM graph shows just slightly hotter signal brings the unit into
deeper clipping and the symmetrical clip brings in more odd harmonics
and involves more upper harmonics.
These graphs illustrate that tube circuits do not just create even harmonics
and that they don’t just create low order harmonics, nor does clipping just produce
odd harmonics. It is a little more complex than that. It depends on the topology,
circuit details, levels and measurement techniques.
What matters in this case is the lack of harmonics before clipping (low THD) which
is not graphed here because it is just a boring noise floor
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