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Old 11th March 2006, 10:48 AM   #1
bappe is offline bappe  Sweden
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Default My JFET project

Hi!

This is what i plan to put together when i get my hands on a few LU1014Ds.

BR,
Anders
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Old 25th July 2006, 05:41 PM   #2
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I'm assuming this is a balanced design? Where are the inputs?
I'd really like to come up with a LU1014D design that can
drive my 4 ohm Carver Ribbons, maybe even with super-
symmetry. Would I need to parallel the VFETs and use something
rated higher than the IRFP240's?
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Old 27th July 2006, 02:49 PM   #3
bappe is offline bappe  Sweden
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The input is at the connection between the 100k and 100 ohm resistors at the jfet input. This one would have no problem driving 4ohm speakers.

BR,
Anders
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Old 29th July 2006, 11:31 PM   #4
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Anders,

Excellent concept,

I bit like a balance follower idea using the cascoded power Jfet.
Please keep us informed with your project.

Macka
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Old 24th January 2007, 11:59 PM   #5
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Anders,
Have you received your LU1014D s yet?
I have mine already and also have some 800 watt Astec MVP
switchers with two of the 24V 15A modules per chassis.
I couldn't tell if your rails are +36v and -36v or +36v and -3v?

I still think that because of the impedance that I will need
to parallel about 4 of the FETs so that they are biased at
the most linear point as in Nelson's Zv9

Anybody else know anything about the Astec MVP series for
audio?
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Old 25th January 2007, 12:16 AM   #6
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It does not appear to me to be biased heavily enough to handle a 4 Ohm load well. That's not too difficult to fix, though.

Grey
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Old 26th January 2007, 07:35 AM   #7
bappe is offline bappe  Sweden
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Default Project progression

Hi!

The amp was built the way it is shown in the first post and showed real promise sonically, it was running a bit hot with the heat sinks i had laying around though. To tackle that problem i decided to choke load it. This dropped the idle power by 50% AND it sounds better to my ears. I have also built one more jfet amp that you can see below, this one is not a transconductance amp and it is also quite happy as high bias class-B amp (500 mA or more). It sound is not quite as relaxed as the other two but it has more "grunt" and drive and i am using it now for bass only. The one below is the class-A version, in the class-B version i have removed the 0.5 ohm source resistors and inserted a bias supply in front of the output stage.

Regards,
Anders
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Old 26th January 2007, 12:33 PM   #8
flg is offline flg  United States
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A hybrid Circlotron Nice
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Old 26th January 2007, 09:32 PM   #9
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Looks good to me. Are the 100pF caps at the Gates of the LU1014Ds necessary?

Grey
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Old 27th January 2007, 08:52 AM   #10
bappe is offline bappe  Sweden
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They are not really needed whith the tube input stage, driven as a buffer from my signal generator they where so i kept them just in case.

Anders
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