What makes different amps produce different sound?

Just for the record, there is a school of thought (and a rather well-credentialed one) that holds that competent amps operating within normal limits do NOT sound different at all. To be more specific, they would argue that if two amps sound different, it will be for one of three reasons:
1) Their levels are not matched.
2) One or both has a frequency response that seriously diverges from flat (as might happen with amps with a high output impedance driving certain loads).
3) One or both is clipping.
Of course, lots of audiophiles reject this, as is their right.

Since every amp sounds different that's probably the reason people reject that idea. There are many people who think nothing sounds different and that there is no reason to buy anything but a Bose Acoustic Wave Machine.

The same equipment in a different room sounds different.

I bought a highly regarded pair of speakers once based on a review. I sold my other speaker to facilitate this change. When the speakers arrived I hooked them up, let them break-in and then sat down to listen. I almost cried since I was a struggling music lover on a very tight budget and these speakers sounded terrible at best. At a loss to know what else to do, I rewired them with some audioquest wire I had left over from some evil experiment I had conducted on an unsuspecting victim.

I hoped for an improvement, but what I got was much more. These speakers actually sounded good. I kept them for some time before moving up to something else.

The point of all this is to say that something as seemingly inoccuous as wire can make a huge difference. When two amps with similar design use different componants they will sound very different.

Consider too, the companies that modify CD players with new caps and resistors. People swear by these mods, or was it that they swear about the mods... I can't remember.

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".