What makes different amps produce different sound?

Hi Jeff,

One design in particular, negative feedback has a rather substantial effect on sound... way back, adding massive amounts of negative feedback was a popular way to woo a consumer by drastically reducing THD or Total Harmonic Distortion... In reality, anything below 1% THD is considered (by most) to be inaudible... negative feedback seems to greatly reduce the 3D soundstage abilities of an amp... other features such as high current can sound different based on the power consumption needs of a particular pair of speakers...

There are a multitude of different design philosophies, each seemingly providing the silver bullet to fidelity. Nelson Pass has his own philosophy and mentions a list of amp fads and design issues in his owner's manual for my Aleph 3. The link is www.passlabs.com/pdf/aleph/a3man.pdf. Look under the "Product Philosophy and Design Theory" section. Here's an excerpt:

"We have heard Triodes, Pentodes, Bipolar, VFET, Mosfet, IGBT, Hybrids, THD distortion, IM distortion, TIM distortion, phase distortion, quantization, feedback, nested feedback, no feedback, feed forward, Stasis, harmonic time alignment, high slew, Class AB, Class A, Pure Class A, Class AA, Class A/AB, Class D, Class H, Constant bias, dynamic bias, optical bias, Real Life Bias, Sustained Plateau Bias, big supplies, smart supplies, regulated supplies, separate supplies, switching supplies, dynamic headroom, high current, balanced inputs and balance outputs...Leaving aside the examples of marketing hype, we have a large number of of attempts to improve the sound of amplifiers, each attempting to address a hypothesized flaw in the performance."

A number of these is addressed in his subsequent comments as he describes his design rationale for the Aleph 3.

Tube amplifiers characteristically produce second harmonic distortion whereas transistors like to produce the third harmonic. Musical instruments typically make second harmonic sounds, so the tube amplifier distortion, even if rather high, is often perceived as pleasant or "musical".

Eldartford: Where did you get that information? To my (admittedly limited) knowledge, everything you've said is wrong. Most instruments produce ALL harmonics, but some wind instruments, if I'm not mistaken, produce only ODD harmonics. (Remember that the fundamental tones are themselves odd harmonics!) Also, while it is true that tube amps tend to have more even harmonic distortion than odd (or is it the other way around?), tube tend to have more of BOTH even and odd-order harmonic distortion than typical solid state designs.

Why anyone thinks that added distortion of any kind should make something sound more musical is beyond me.

I think it was Art Dudley who suggested that the color of the face plate had an effect on the sound of amps and preamps.