My JFET project

bappe · 11th March 2006, 10:48 AM

Hi!

This is what i plan to put together when i get my hands on a few LU1014D´s.

BR,
Anders

coloradosound · 25th July 2006, 05:41 PM

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?

bappe · 27th July 2006, 02:49 PM

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

macka · 29th July 2006, 11:31 PM

Anders,

Excellent concept,

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

Macka

coloradosound · 24th January 2007, 11:59 PM

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?

GRollins · 25th January 2007, 12:16 AM

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

bappe · 26th January 2007, 07:35 AM

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

flg · 26th January 2007, 12:33 PM

A hybrid Circlotron

Nice

GRollins · 26th January 2007, 09:32 PM

Looks good to me. Are the 100pF caps at the Gates of the LU1014Ds necessary?

Grey

bappe · 27th January 2007, 08:52 AM

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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25th July 2006, 05:41 PM	#2
coloradosound diyAudio Member Join Date: Nov 2005 Location: colorado	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?

27th July 2006, 02:49 PM	#3
bappe diyAudio Member Join Date: Sep 2002 Location: Furulund, SWEDEN	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

29th July 2006, 11:31 PM	#4
macka diyAudio Member Join Date: Dec 2001 Location: Australia	Anders, Excellent concept, I bit like a balance follower idea using the cascoded power Jfet. Please keep us informed with your project. Macka

24th January 2007, 11:59 PM	#5
coloradosound diyAudio Member Join Date: Nov 2005 Location: colorado	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?

25th January 2007, 12:16 AM	#6
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	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

26th January 2007, 12:33 PM	#8
flg diyAudio Member Join Date: Jul 2005 Location: North East	A hybrid Circlotron Nice

26th January 2007, 09:32 PM	#9
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Looks good to me. Are the 100pF caps at the Gates of the LU1014Ds necessary? Grey

27th January 2007, 08:52 AM	#10
bappe diyAudio Member Join Date: Sep 2002 Location: Furulund, SWEDEN	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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