Cascode topology for Power Output like STASIS - no longer used in today's amps; why? - diyAudio
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Old 14th October 2009, 11:51 AM   #1
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Default Cascode topology for Power Output like STASIS - no longer used in today's amps; why?

Both in commercial as well as diy currently power amplifier circuits there are no longer power cascode output stage in use , such as e. g. in "Stasis" and "CAS" circuits. What is the main reason for this? Here two weblinks for quickly find the advantages:
http://www.firstwatt.com/downloads/cascode.pdf
stasis 2 and 3 schematics
(schematic page 2 #19)
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Old 14th October 2009, 11:10 PM   #2
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Quote:
Originally Posted by tiefbassuebertr View Post
Both in commercial as well as diy currently power amplifier circuits there are no longer power cascode output stage in use , such as e. g. in "Stasis" and "CAS" circuits. What is the main reason for this?
That's a good question. I think it has more to do with fashion
than technology. The first Stasis amps were pretty warm but
not so dynamic. Later, it was apparent that the market was
buying dynamics, as in Krell and Levinson, and cascoding
the output stage appeared to be compressing the dynamics.
Don't ask me why - that's just what we heard.

So the cascoding of the output stage was dropped and
beefier Motorola MH15022's and such put in, and the sound
became more dynamic. Stasis amplifiers were shipped that
way thereafter.

When I formed Pass Labs, I decided that there was enough
in the way of dynamics in the market, and I was tired of
that anyway, so I began pursuing a different sort of sound,
and what I came up with managed to fit the wants of a
segment of the market, and here I am today.

Where does that leave Cascoding? Still a viable tool. ZV9
(the DIY F3) used cascoding and Cascode Modulation (tm)
to good effect. Perhaps someday it will become very
dynamic sounding...

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Old 22nd October 2009, 11:39 AM   #3
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Quote:
Originally Posted by Nelson Pass View Post
The first Stasis amps were pretty warm but
not so dynamic. Later, it was apparent that the market was
buying dynamics, as in Krell and Levinson, and cascoding
the output stage appeared to be compressing the dynamics.
Don't ask me why - that's just what we heard.

So the cascoding of the output stage was dropped and
beefier Motorola MH15022's and such put in, and the sound
became more dynamic. Stasis amplifiers were shipped that
way thereafter.
Thank you for those comments, Mr. Pass.

Currently I'm trying to compile schematics from all Threshold devices (from the "400A/800A" to the presently models), and unfortunately I do not get it from all the exist models in whole or in poor resolution handcrafted sketching.
But I discover in some cases (for the aim of protection) a serial fuse between the power output and the speaker terminals (e. g. Stasis 3), have a look about the URL
Imageshack - regalorgikea3yi.jpg
That usually causes the effect you describe. Especially if I have loudspeakers with complex character (colored sound) or very low impedance like some types of Infinity Kappa series.

Could this be perhaps the real cause for your described lack of dynamic and not the cascode topology?

Last edited by tiefbassuebertr; 22nd October 2009 at 11:43 AM.
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