[richidoo]

Woke up thinking about this today, output impedance of linear ss amps v. switchers. Curious to hear that Spectron...

Let's say a tube amp with a good transformer has output impedance of 1 ohms. A bipolar SS amp has outputZ of 0.1 ohm. And a switching amp has outputZ of .01 ohm.  Let's say speaker load is relatively flat around 4 to 8 ohms and a decent quality, short length speaker wire with minimal reactance.

It is usually obvious to hear the difference between the tube amps and the linear SS amp in damping control, with output Z is ~10x lower. Bass is tighter, cleaner, more impact, etc.

But how 'bout comparing the linear SS amp at 0.1 ohm to the switcher at 0.01 ohm? Still 10x lower again, but now the absolute magnitude of the difference is also 10x smaller than with the tube/linear. So is the difference in damping with linear/switcher just as audible as the difference heard between tube and bipolar output stage? What matters more, the impedance ratio which is increased 10x, or the absolute impedance, which has only decreased by ~1/10ohm. I guess they are the same in essence, but what is proper way to view it? Ratio, I bet...

Are these awesome specs for switching amps really significant? Or is typical SS output impedance close to the peak of the audible benefit?

People continue to rave about switchers' great bass performance, even compared to good ss amps. Is lower output Z a major reason why?

Thanks - and TGIF, have a great weekend everybody!
Rich

[Steve]

Hi Rich,

    The ratio of .1 to .01 will not be as noticeable as one has to figure in the speaker , Xover and wire impedances.

In the cases you site above, let's say the speaker impedance is approx 4 ohms, for simplicity sake. 4.1 vs 4.01 (1.0224 ratio) is not as much difference as 5 ohms vs 4.1 ohms (1.22 ratio).

Hope this helps Rich.
Steve

[*Scotty*]

richidoo  My answer to your last question,"People continue to rave about switchers' great bass performance, even compared to good ss amps. Is lower output Z a major reason why?" Possibly. The Tripath amp I used to use had only one large pair of Mosfets in each channel. There were no resistors in the output stage at all, so the real world output impedance before feedback is applied is very low and apparently the propagation delay in the feedback loop is also very low. Both of these factors could contribute to the amplifiers transparency and bass quality. Another factor that contributes to the bass is that the amplifier is around 90% efficient and does not load down the transformer by having bias current in the output transistors.
This is like having a Class AB amplifier with a much larger transformer, perhaps as much as 40% larger. A Class D amp with a .5kva is roughly equivalent to a Class AB with a .8kva transformer depending on how far it is biased into Class A. I am addicted to the bass quality that the Tripath amp had, but it had a slightly harmonically threadbare midrange caused by the switching delay between turning one output device on and turning off the other one already in use. This is called dead-band  time by Tripath. The midrange could be improved by reducing the deadband time, but you had to have a gap between turn off and turn on to prevent a dead short in the output stage in the Tripath amp I had.
Scotty