Translation needed

[lumanauw]

I found an old article, by Norman H. Crowhurst originally in Audio magazine may 1959, title " The amplifier distortion story", re-printed in Glass Audio volume 7 no.6 1995.

He based his writings on tubes.

Anyone can translate how would his writings like if "tubes" are replaced with "transistors"?

[richie00boy]

Without seeing the article it's difficult to comment, but probably the two are not really interchangeable because of their different law and transconductance characteristics.

[sreten]

Hi,

If I remember correctly that is the article that states THD (total
harmonic distortion) (+noise) as a figure is entirely misleading.

He suggested harmonics should be weighted logarithmically.
The most common accepted form is by (n sqared) over 4.
That leaves second harmonic as its real value, 3rd = x 2.25,
4th = x 4, 5th = x 6.25, 6th = x 9, 7th = x 12.25, 8th = x 16 etc.

This has serious repercussions for standard solid state amplifiers.
They routinely produce harmonics at least up to the 20th (x100)
for 1kHz crossover distortion, and due to the nature of standard
feedback the higher harmonics are emphasised, they double in
level for each octave.

Not surprisingly with the advent of the new fangled transistors
giving power amplifiers with lower THD+N than valve amplifiers
the significance of such work was quietly ignored.

The claim is his work only applied to the first few harmonics
of valve amplifier distortion, and cannot be applied to the
crossover distortion of transistor power amplifiers.

Me, I think it can, and does apply to transistor power amplifiers.

, sreten.

[richie00boy]

Well now I've seen that abstract I would have to agree with sreten. The higher the order of harmonic the worse the shape of the in/out curve is along it's whole length which says more about linearity range. A more simple deflection of the in/out curve would yield a lower order but possibly higher level (which seems to be more benign) distortion. So it seems fair to say higher harmonics are worse and weight them accordingly.

Distortion and harmonics are the same evil whether the amplifying device is valve or solid state.

[lumanauw]

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