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Damping factor - tubes versus solid state?



 
 
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  #1  
Old December 3rd 03, 07:04 PM
Scott Gardner
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Default Damping factor - tubes versus solid state?

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

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  #2  
Old December 3rd 03, 08:24 PM
Chris Berry
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yes. 300 or so is good - the more the better.
cb


  #3  
Old December 3rd 03, 08:57 PM
Tim Williams
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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.

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
>



  #4  
Old December 3rd 03, 09:52 PM
Andy Evans
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I was reading about this re the Menno van der Veen post about super-triode and
super pentode circuits as he calls them. Have a look at these figures!
http://www.plitron.com/PDF/PB/Article/Atcl_4.pdf

The damping factor for tube circuits (8 listed) goes from .05 to 2.5 with no
global feedback.


=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.
  #5  
Old December 3rd 03, 10:13 PM
Patrick Turner
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Scott Gardner wrote:

> 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?


triode amp without FB can be built to have a DF of around 5,
which satisfies a lot of people.

With around 12dB of FB, their DF can be say 10, or 20.
Other tube amps running in UL or pentode
need around 16 to 20 dB of FB to get the same DF as a triode amp.

SS amps with a total of 80 dB of FB manage DF = over 100.

Once the DF rises above 10, I doubt too many folks can hear any
difference.

Patrick Turner.

>
> Thanks,
> Scott Gardner


  #6  
Old December 4th 03, 02:28 AM
123 123
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That's just an accidental by-product of the types of components, Scott.
Once you go into double figures, you have much more than enough damping
already. It is a mistake to make damping into a single measure of the
goodness of an amp, sometimes done by commercial interests because it is
so easy. They're generally the same guys who will pile on the feedback
regardless, until they've turned what should be a lobster dinner into
goop. Many ZNFB SE fans are very happy with amps that have damping
factors in the region four or five or six.

Andre

Scott Gardner > wrote:

> 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



  #7  
Old December 4th 03, 09:03 AM
Scott Gardner
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Thanks for all the replies. Between what you all have said here and
other research, I realize now how closely damping factor and negative
feedback are related, hence the typically-higher numbers for
solid-state equipment.

Scott Gardner

On Thu, 4 Dec 2003 02:28:46 +0000, (123 123) wrote:

>That's just an accidental by-product of the types of components, Scott.
>Once you go into double figures, you have much more than enough damping
>already. It is a mistake to make damping into a single measure of the
>goodness of an amp, sometimes done by commercial interests because it is
>so easy. They're generally the same guys who will pile on the feedback
>regardless, until they've turned what should be a lobster dinner into
>goop. Many ZNFB SE fans are very happy with amps that have damping
>factors in the region four or five or six.
>
>Andre
>
>Scott Gardner > wrote:
>
>> 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

>
>


  #8  
Old December 4th 03, 09:41 AM
Phil Allison
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"Scott Gardner" >

> 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)?



** Yep.

> What's a good minimum damping factor that won't introduce
> audible artifacts,



** 50 to 100 is a good range - but the whole DF issue depends on what
speakers you are using.

An ideal power amp is one that can be used with any commercial hi-fi
speaker system without audible change in the output due to variations in the
speaker load impedance with frequency.

If an amp has a specified DF of 10 then that means the output impedance is
0.8 ohms. If a speaker system ( 8 ohm nominal) is used that has a minimum
impedance of 2 ohms at some frequency - which is not that uncommon - then
there will be a 3 dB loss of input level at that minimum. A 3 dB dip in the
mid or high band is VERY audible.

Speaker designers usually assume that a high quality amp is going to be
used - ie a SS amp with high damping factor - so they do not often design
their creations to suit amps with low numbers like 5 or 10.

One major reason why tube amps are claimed to sound "different" is their
low DF figures.



.......... Phil


  #9  
Old December 5th 03, 03:25 PM
Patrick Turner
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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
> >


 




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