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Old 27th May 2006, 09:01 PM   #71
The one and only
 
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Yes, this is definitely a Class A circuit.

As to the cascode, you can approach it either way, I don't think
it's going to make a lot of difference. Self biased JFETs are
elegant, but you have to take the voltage they offer.
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Old 27th May 2006, 10:14 PM   #72
EUVL is offline EUVL  Europe
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May I ask for one more hint ?

Suppose I only want 10-15W Class A (just to drive tweekers), and I want to use Loveltech Power JFETs with Cascode as output, like Grey is proposing. I guess I would be biasing single JFET at 1.3A (2 Power JFETs per channel). Would I still be able to use the triode parts of the curves ? I have no Power JFETs on hand yet, and there is insufficient information on the datasheet. What would be the best cascode voltage ?

Many thanks in advance,
Patrick
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Old 27th May 2006, 11:09 PM   #73
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Of course. You get to the triode part of the curve by operating
at the lower voltages, and the cascoding can easily be set for
any operating point you want. It's just lucky that the spot you
want is 2-3 volts or so, so the dissipation will be low on the JFET.
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Old 28th May 2006, 06:08 AM   #74
EUVL is offline EUVL  Europe
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Any chance of publishing some measurements (Id vs Vds for various fixed Vgs) around that region ?

Most grateful,
Patrick
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Old 29th May 2006, 04:58 AM   #75
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Quote:
Originally posted by Nelson Pass

Kirchoff's Law dictates that the circuit will not work unless there
is some DC attachment from the input circuit to the output
circuit to allow a difference in drive current to the output devices.

Aha . . . Kirchoff's rule . . .

The basic is almost same as shear flow analysis with multicells we are working on it daily.
By the way, I was always confused if the simultaneous linear equaions are more than two. Never improved yet . . .

Regards

JH
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Old 30th May 2006, 06:10 PM   #76
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Quote:
Originally posted by EUVL
Any chance of publishing some measurements (Id vs Vds for various fixed Vgs) around that region ?
You are in the region where it varies quite a bit. If you check
ZV9, you'll get some incomplete information.
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Old 2nd June 2006, 09:47 AM   #77
EUVL is offline EUVL  Europe
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> You are in the region where it varies quite a bit. If you check ZV9, you'll get some incomplete information.

Had done so already before asking. Guess I just have to wait until the JFETs arrive, whenever that might be.

In the meantime, this is the first attempt for the power JFET version. Of course you are right, the MOSFET version published earlier here has very little gain. This should have about 30dB at 4 ohms, and is, at least according to quick hand calculations, stable to over 1MHz.

The over-current protection is probably not quite sufficient, but I have not figured out an elegant way of doing that yet.

Should I expect expect quite a bit of thermal drift for the Power JFETs, bearing in mind their very high transconductance ?


Patrick

Attached Files
File Type: pdf 2 stage circlotron pjx v1 simplified.pdf (76.0 KB, 529 views)
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Old 2nd June 2006, 03:33 PM   #78
EUVL is offline EUVL  Europe
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Firstly my apologies for posting the wrong schematics. It was of course not the one with Power JFET, but the previous MOSFET circuit.

It had taken some time and I still could not make the file small enough for posting, so we'll have to do it in two halves.

This is the overall view.


Patrick
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Old 2nd June 2006, 03:34 PM   #79
EUVL is offline EUVL  Europe
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And the left hand half in pdf.
Right hand half is identical but mirrored.

Patrick
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File Type: pdf 2 stage circlotron pjx v1 simplified hlf.pdf (73.3 KB, 443 views)
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Old 14th June 2006, 07:37 PM   #80
gl is offline gl  United States
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Hi Grey,

How is the development of the New-tron going? There have been lots of ideas floating around on this thread. Have you made any further updates or had any further progress? Thanks.

Cheers,
Graeme
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