[BC] even or odd harmonics

[Robert Orban]

At 08:30 PM 10/1/2009, Broadcast List USER wrote:
>That is because tube amplifiers produce a lot of even harmonics.  Our
>ears LIKE even harmonics.  Solid state amplifiers produce odd
>harmonics (in general).  Our ears detest odd harmonics.  This is why
>the Aphex Aural Exciter is so popular.

A push-pull tube amplifier produces primarily odd harmonics, as does 
any other amplifier that uses a symmetrical topology, including solid 
state amplifiers. If you want even-order harmonics, you need a 
nonlinear device with an asymmetrical transfer curve. Single-ended 
tube or solid state circuits can both do this.

That being said, these days it's fairly easy to make solid state 
amplifiers with nonlinear distortion that's way below the threshold 
of hearing with program material. It's also possible to make a tube 
amplifier with inaudible distortion, but it's more difficult and in 
my opinion, pointless in 2009 unless one wants a piece of "audio jewelry."

If you had the opportunity back in the late '40s or early '50s to ask 
Frank McIntosh about even-order distortion in tube amplifiers, he 
would have explained how hard they worked to get the classic McIntosh 
tube amplifiers symmetrical and linear. They used to advertise them 
as "the amplifiers without the 'brrr...'".

Bob Orban