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Old 28th September 2004, 02:16 PM   #11
bocka is offline bocka  Germany
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Hi Konrad,

the schematic you've posted ist not a folded cascode. It's a simple two stage amplification design with sym longtail input stage, VAS (Q3 and Q6) and an output stage. Minor changes can make a folded cascode.
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Old 28th September 2004, 02:30 PM   #12
MikeB is offline MikeB  Germany
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Hmm, except q10 & q5 and the outputstage its identical to mine ?
X7 & X8 are a bit unluckily, but was already mentioned ...

Mike
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Old 28th September 2004, 02:54 PM   #13
Konrad is offline Konrad  Norway
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Quote:
Originally posted by bocka
Hi Konrad,

the schematic you've posted ist not a folded cascode. It's a simple two stage amplification design with sym longtail input stage, VAS (Q3 and Q6) and an output stage. Minor changes can make a folded cascode.

Ypp. I simply dont see the great benefits of folded kaskode. I prefer the buffered OTA (all symetric).
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Old 28th September 2004, 02:59 PM   #14
Mr Evil is offline Mr Evil  United Kingdom
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Quote:
Originally posted by Konrad
...Faster off, a tiny litle help from a transistor. Here in the att: Q5 and Q8...
Ahah! That really works, thanks.


Quote:
Originally posted by MikeB
Hi mr.evil !

You might have a look here:
Have you ever succeed in buiding a input stage with current mirror?

But good that you opened a thread for folded cascode...
It's a very interesting topology ! And my prototype of a symetrical
folded cascode is already running !

Mike
I do like using unusual topologies. If they happen to work well too, then that's an added bonus.


Quote:
Originally posted by bocka
Hi Konrad,

the schematic you've posted ist not a folded cascode. It's a simple two stage amplification design with sym longtail input stage, VAS (Q3 and Q6) and an output stage. Minor changes can make a folded cascode.
Are you sure? Q9/10 and Q4/5 are connected in common-base configuration. They follow after Q13/14 and Q2/6, which are CE. CB following CE is the definition of a cascode, if I recall correctly.
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Old 28th September 2004, 03:02 PM   #15
MikeB is offline MikeB  Germany
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oops, i didn't realize that konrad's circuit was referenced by bocka,
this is not a real folded cascode.
Folded cascode has the advantage of being superfast, thus creates
a perfect gain/bandwidth/phaseplot. This gives superb performance
on trebles, the big weakness of most SS-amps.

Mike
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Old 28th September 2004, 03:51 PM   #16
bocka is offline bocka  Germany
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Hi Mr. Evil,

I was refering to the circuit Konrad has attched. Your design is a folded cascode.

Mike:

Welcome to the folded cascode topology club! To my opinion it has several advantages. When you cut the folded cascode into an upper and a lower half, it contains only one amplifying transistor in each half (electrically these two transistors are paralled). This is the main reason why the folded cascode sounds better (to me) than any other topology. The first diff amp only produces K2 and K3 and this signal ist not fed into another amp stage which distorts and produces high order distortion. If you compare it to SE triode tube design, it has a similar topology. Unfortunately "PNP" tubes not exist.

Because it has only one amplification stage the folded cascode is theoretically stable into any load. Practically it needs some work to do so but I build amps which are extraordonary stable with a very low output inductor and drives high capacitive loads up to several uf. When you want to "colorise" the sound try to use highest quality feedback resistors as well as micas for the feedback and compensation caps. The folded cascode is really worth it and it shows the differences of these components very clearly. Also try to increase the driver and bias currents. The more the better.
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Old 28th September 2004, 04:03 PM   #17
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I'm new to the folded cascode, and it looks an interesting topology.

If you have the supply rails available though, a conventional cascode stage followed by a current mirror to change the output to be ground referenced (rather than referenced to the supply rail) seems to give better performance. At least SPICE says so!

Any comments regarding folded cascode versus conventional cascode + current mirrors?
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Old 28th September 2004, 04:06 PM   #18
MikeB is offline MikeB  Germany
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Hi bocka !
Yes, i look forward to finetuning the circuit, i hope i get the same
performance for mids like my other symamp. For trebles the folded
cascode definitely outperforms all amps i have access to.
At this moment my amp sounds too "dry", but it's the first version
and there are many possibilities for optimizing sound. I haven't
really adjusted the feedbacknetwork yet, in my experience the most
important thing for good sound...

Mike
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Old 28th September 2004, 04:26 PM   #19
mlloyd1 is offline mlloyd1  United States
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Default i am curious ...

I haven't played with "official" folded cascodes in a power amp yet. I have played around with circuits simular to what Konrad posted, also shown on Borbely's web site. Overall, I've been pretty happy with the results.

I have read a number of comments here and elsewhere about sonic benefits of folded cascodes topologies. I am curious if anyone can pose sound theories as to why folded cascodes have not caught on in a bigger way among the "I make a living at it" audio design community (Nelson Pass and Jeff Rowland excluded, of course, there may be others?).

mlloyd1
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Old 28th September 2004, 04:32 PM   #20
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Default I know of a few more...........

But then, we may be friends, and birds of a feather.................

(Actually, JR is into something else these days.)

Jocko
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