[sdiy] Request brain dump on balanced lines

[jhaible]

> But more practically, most amps work in a balanced configuration that
> cancels out all odd order distortion products, depending on how well
> balanced things are.

If the 3rd harmonic would be so much more unpleasant than the 2nd
harmonic, there would be no such rule as trimming amps for
symmetrical clipping. (I don't know which is wrong, 3rd harmonic
being worse than 2nd, or the goal to have symmetrical clipping.
Just wanted to point out that both can hardly be right at the same time.)

> Further, this explanation assumes that our sense of hearing cares a lot
> about harmonic distortion, which is not necessarily true.

I fully agree. But maybe the ear cares for a sudden change of harmonics.
And higher harmonics will come and go much faster than lower harmonics
when the amount of overdrive changes. I think this is generally so, because
the Nth harmonic is created by the x**N term in the Taylor description
of a transfer courve. So the fundamental is just amplified like it should,
the 2nd harmonic comes in with input_amplitude**2, which is still rather
smooth, but a 7th harmonic comes with input_amplitude**7, which is
almost like a hard switch. Maybe that's the main reason for the "scratchy"
sound of a distortion that contains a lot of higher harmonics: not the
harmonic
content by itself, but the sudden change of harmonic content.
Does this make sense?

JH.

-----Ursprüngliche Nachricht-----
Von: Don Tillman <don at till.com>
An: <madhun2001 at yahoo.com>
Cc: <debus at cityweb.de>; <synth-diy at dropmix.xs4all.nl>
Gesendet: Sonntag, 13. Oktober 2002 22:29
Betreff: Re: [sdiy] Request brain dump on balanced lines


>    > Date: Sun, 13 Oct 2002 10:47:05 -0700 (PDT)
>    > From: Tim Ressel <madhun2001 at yahoo.com>
>    >
>    > The best explanation I have heard is this: all semiconductor
>    > amplifiers add 3rd harmonic distortion, which is unplesant to the
>    > ear. Transformers tend to add 2nd harmonic distortion (as do tube
>    > amps), and 2nd harmonic distortion is pleasant to the ear.
>    >
>    > There are as many opinions on this as there are people, but this
>    > explanation makes sense to me.
>
> Really?
>
> If a tube stage was exactly a square-law device it would only have 2nd
> harmonic distortion.  But tubes aren't exactly square-law devices,
> more like 1.5-law, so a single tube stage does contribute third
> harmonic distortion.  And if there's feedback involved, that will also
> change the distortion products.  Multiple stages changes the
> distortion products more.
>
> And a single transistor stage has significantly more 2nd harmonic
> distortion than third.
>
> But more practically, most amps work in a balanced configuration that
> cancels out all odd order distortion products, depending on how well
> balanced things are.
>
> Further, this explanation assumes that our sense of hearing cares a lot
> about harmonic distortion, which is not necessarily true.
>
> So while this explanation is the popular one -- it comes from that
> engineering math class where you get to derrive the Fourier spectra of
> exp(sin(wt)) and (sin(wt))^2 -- I think it completely lacks
> credibility.
>
>   -- Don
>
> --
> Don Tillman
> Palo Alto, California, USA
> don at till.com
> http://www.till.com
>
>