Please explain amplifier output impedance

There is no hard and fast threshold but IMO, anything over 1 ohm is definately high output impedance. Many SS amps will be about 10x lower and tube amps are up to 10x higher so 1 ohm threshold seems to a decent rule of thumb.

Sean - My comment about amp impedance rising above 50kHz was based on at least a 3dB rise so it would visibly start to deviate around 20kHz. And you are definately correct in saying that many amps can't even do that well. I read all the Stereophile measurements several times each, no matter the piece of equipment. I am happy they are still around to do the good old fashioned measurements, even if I realize they aren't very applicable to musical reality. Nonetheless, I feel there is a lot to be said for an amplifer with an elegant set of curves.

Arthur

High damping factor is allways desirable. Since speakers are a reactive load they respond to the amplifier signal with a counter eletromotiv force that the amp must deal with, and with a low damping factor the amp will have more intermodulation distortion because of this fact. Low damping factor will cause the amp to have more problems in controlling the speakers drivers properlly.

Yes, it is impossible to make voltage without current. Power=Voltage X Current. Even in a preamp the voltage is there because current is there also. This fact is inescapable and is the result of Ohm's Law, the basic law of all electricity.

The reason Negative Feedback does not work is two-fold. Propagation delays inside all audio amplifiers insure that negative feedback arrives with a delay with respect to the input signal its supposed to provide correction for. At bass frequencies this problem is not profound, but at treble frequencies it is responsible for added odd-ordered harmonic content which (although in small levels) is something that the human ear uses as loudness cues- in effect a source of unnatural harshness to the human ear.

Negative feedback runs counter to the rules our ears use and we're stuck with the ears we have. If we could eliminate the propagation delays inside audio amplifiers and gain stages, NF would work, but until then Negative Feedback is a failed concept.

10-10-06: Atmasphere
The reason Negative Feedback does not work is two-fold. Propagation delays inside all audio amplifiers insure that negative feedback arrives with a delay with respect to the input signal its supposed to provide correction for. At bass frequencies this problem is not profound, but at treble frequencies it is responsible for added odd-ordered harmonic content which (although in small levels) is something that the human ear uses as loudness cues- in effect a source of unnatural harshness to the human ear.

I believe it is this issue that Dakiom Feedback Stabilizers claim to correct. I have no idea if they work as advertised on amplifiers.

I've specifically mentioned the Td ( Time delay ) of a circuit that Ralph makes mention of several times in the past. Shorter signal paths with a consistent impedance will have a lower Td, which is a good thing. I only know of one manufacturer that has ever published this spec as standard procedure.

Speed and time delays are one of the reasons why local feedback works "better" than global feedback. That is, local feedback isn't as slow to respond and the correction factor is smaller in amplitude. On the other hand, global feedback is both slower with greater correction factors involved, making it less desirable. No matter how fast the error correction rate is, it is NOT "instantaneous". As such, it has the potential to introduce other distortions into the equation. Kinda funny how circuitry that is designed to cancel distortion can actually introduce distortion, isn't it???

As far as having maximum voltage with minimal current flow, this is definitely a reality. If such were not the case, we wouldn't have to worry about such things as arcing or corona. Yes, there is current flow involved, but it is minimal compared to the amount of voltage involved.

Try to measure the resistance of air by holding two test leads a few inches apart. With that high of a resistance ( next to infinity ), the current flow involved in arcing across that gap would be quite low even though the voltage required would be quite high. Kind of an extreme example, but i used this as i thought it would be easier to understand than trying to explain antenna theory : ) Sean
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