Tim Williams wrote:

Yes, same way. DF more than a few is useless as speakers have a DC
resistance in excess of a few ohms, resulting in their impedance
never dropping below that value. Odd crossovers might skew it though..

The most I can see you'd ever need is 10 (i.e. .8 ohm Zo vs. 8 ohm
speakers). SS only has a high DF due to its design.

Indeed the design makes low Ro easy with SS, because of the high level of
NFB.

But in fact, collector resistance is high compared to the loads
that are used with bjts, rather like pentodes have a high plate resistance
compared to load value, and in effect, bjts are
current sources, not voltage sources, like triodes.

In old radios, where there was say a 6V6 used as the beam tetrode output
tube,
there was often no NFB loop.
The speakers used blended well
with current source drivers.
The bass resonance gave a bit of a rise in the bass, where you could do with
it,
and the rising impedance and acoustic output with rising frequency
meant the roll off in amplifier and radio AF bandwidth response was
compensated for
by the speaker characteristic.
The net result was tolerable radio on the mantle peice
telling us about WW2, the cricket, or baseball scores.
Some such radios are remarkably listenable,
but for complex music over a watt, they are awful, with distortion
products being such a high level that they exceeded the natural HF content
of the program.

If NFB is applied in such a radio, often the sound is worse,
bnecause the bandwidth is reduced further, since it isn't boosted
"artificially".
The answer is to use full range speakers where FB is employed.
This approach makes old radios sound a lot better.

If the Ro of an amp is 0.8 ohms, ie, DF = 10, for an 8 ohm speaker,
the DF when RL = 4 ohms is only 5.
Or its 40 whan the bass impedance rises to say 32 ohms.
So quite a bit of eq occurs if the speaker Z varies a lot.

But not a single speaker has a flat response, and all have
dips and peaks, and it would be sheer luck that an amp
with high Ro would result in interacting with a given speaker
to make its response flatter.
I am in favour of a DF of at least 10, with a 5 ohm load,
preferably 15.

Speakers are usually designed to have a low Ro feed for the
designed output.
Some I have tested have a deliberately engineered contour
to give them a "loudness profile", ie some extra treble and low bass,
to make then have presence, but a highish Ro amp
may not fix that problem, and it is a problem.

Patrick Turner.



Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"Scott Gardner" wrote in message
...
I've noticed that solid-state amplifiers tend to have much
higher damping factors than tube amps. Is damping factor measured the
same way for both types of amps (load impedance divided by output
impedance)?
What's a good minimum damping factor that won't introduce
audible artifacts, and is that minimum number the same for both
solid-state and tube amplifiers?

Thanks,
Scott Gardner