F2J JIG using Depletion Mode JFETS.

[Zen Mod]

DC is lowest line on right
then you have 10mS, 1mS, 100uS .........

 

[twitchie]

You already knew this Canuck is the blind one

 

[EUVL]

Of the 2 devices you listed, the UJ3N120070K3S should work nicely.

Datasheet from Mouser says Vgs = -12V at ~1A. So depletion mode.
Or I misunderstood what you said ?


Patrick

 

[EUVL]

You can use a MOSFET gate driver opto-coupler like the Vishay VO1263

Are you sure they deliver enough current to drive the capacitances of the FETs at low voltage ?


Patrick

 

[EUVL]

A simple way to measure the intrinsic distortion of these depletion devices is wire them as a follower.
Feed it with a sine wave signal and measure the distortion spectrum under load.
Also possible to measure gate leakage across the gate stopper.

Also possible for the enhancement mode devices, but a bit more complicated at the input side.


Patrick

.

 

[myfirstamplifier]

Seems to want to go in spice eh! I'm going to order some parts and tinker with it this weekend.

 

[myfirstamplifier]

FWIW, I found that ONSEMI has quite a large selection of SiC Mosfets:

https://www.onsemi.com/products/discrete-power-modules/silicon-carbide-sic/silicon-carbide-sic-mosfets

 

[petoluk]

I'll try with UJ3N065080K3S

This was already mentioned elsewhere, but while the UJ3N065080K3S is the cheapest of the 5 in-production USCi JFETs, hence, not such a huge sacrifice if it goes up in flames during mad experiments , the UJ3N120065K3S at ~2x the price is the only one of the quintet with a more reasonable VGS(th) of around -6V.

It's a pity though this new series of JFETs all have negative VGS(th) tempco, unlike the previous, now obsolete UJN1205K, UJN1208K or UJN171K0K...

 

[claudio52]

I played a few years ago with UJN1208K. Now it rests in a drawer along with an IRFP9240 and a TL431. It's an ultra simple DEF. It worked very well. The PSU was a lab power supply

as a lab power supply.

 

[andynor]

Hi All!

I'm looking at trying to cobble together an F2J JIG that I can test UnitedSIC JFETS with. I'm not looking for the magical "Triode" like behaviour or any special tones. Just an amplifier of around 5 Watts with a relatively low distortion figure and can drive 88dbw/M speakers 6 OHM. (Paradigm Signature Reference S2) I spoke with Mr. Pass (Papa Pass) and he stated I can just plug them in and tinker and warned me about using depletion mode JFETS (which I have studied in class A self biasing modes) in the f2J, however he chose a rare variety of enhanced mode JFET. I asked my professor about these and he said they don't exist and told me to start designing with common parts! So, I looked into it further and actually they are mostly normally off devices (the common JFET needs a few volts negative to turn it on!) well... yes.. hes correct in that ALL of our tests and labs we are using small signal JFETS which are only depletion mode devices and enhancement mode devices are usually strictly Mosfets and further I learned today that they are now discrete cascode MOS/JFET design. (UJ4C075060K3S) which is actually a JFET/MOSFET in the same package. 🤔

My main idea for this year end project was to demonstrate a small 5w Amp using PAPA F2J to my class but instead of trying to find or buy rare R100 Semisouth devices I wanted to use something common like depletion mode devices from UnitedSiC, biased in CLASS A with liquid cooling; more specifically these SiC depletion devices I found and are easily available to me: UJ3N065080K3S or UJ3N120070K3S

Using his production ready circuit and trying to "plug in" these devices will not work as the original F2J is using rare enhanced mode JFETS with positive bias on the gate, so...

My question what is the most elegant way to develop negative bias to the gate using a simple bench power supply? Obviously, Opening R4 and directing it to a negative voltage regulator source came to mind? Is there anything else I need to change in the F2J layout so that I can save some time and headaches with my project? I am seeking to demonstrate a low noise and low THD CLASS A amplifier with a liquid cooling system.

I hope to learn and build with modern Silicon Carbide or GaN devices so please go easy on me!

Thank you so much.

Jeff

Check PM, clue is there to perhaps move your ambition to the next level or two 🙂

Existance has always been relative.

 

[myfirstamplifier]

for F2J -- I am closer to get getting all the parts to try DEF and F2J. I was wondering what is the best way to get 10w instead of 5w from this design? I feel like I need the extra power because my speakers not easy to drive.

 

[Zen Mod]

Don't use force, use a bigger Hammer

speakers not easy to drive, F2 no bueno

 

[ripson]

I am experimenting with LTSpice to bias the depletion devices in F2 (including 2SK82 without a degeneration resistor). However, it is not acting as precisely as F2 with enhancement devices as a current amplifier.

I like what Mark Johnson did on his Theseus project with a DC-to-DC converter to get 5V negative voltage without the need for an extra transformer winding

How is the DKW amp going? 🙂

 

[Zen Mod]

DKW still sleeping on shelf, same as several new ones

Well, that's life of ZM