2SK53 FET

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Japanese Industrial Standard JIS : K is always N

Ah, you're saying you can't tell from the JFET connections in the CPY-2 ? :clown:
 

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In fact, I had to open the cartridge which was full of glue inside. I worked with a needle to take out the glue. I cleaned perfectly the inside so I could replace the fets but the little wires that goes to the little circuit were broken during the process.

The Stax adaptor feeds 9.6V to left ground (LG) and right ground (RG)of the cartridge. The V+ goes to the (LG) and the ground of the supply goes to (RG)

From RG, two 30K resistors goes to right hot (RH) and left hot (LH)

I don't know if the two 30K resistors go to the drain or source of the fets.

On the 4 pins that go outside the cartridge, there's a ground that goes from the cartridge conductive body , There's LH and RH output signals, (which have 30K that goes to ground of the power supply.

The problems I have is that normally, the V+ goes to the Drain with the resistors. In this cartridge, the two resistors are connected to the ground of the power supply instead of the V+

I know that the bias leakage current affect the gain of this cartridge.

Best should be to draw the schematic if you have an idea how to connect the wires.

Thanks a lot
 

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Not sure if this helps you or not but the drain and source of a JFET are interchangeable as the device is symetrical.

This was something I long wondered over as I noticed circuits performed identically whichever way they were fitted.

The late and much missed Bob Pease confirmed that they are indeed symetrical and you can not tell which is Drain or Source for most JFET's
 
Finally with all the informations I had, I figured that the fets in this cartridge are used as source followers like it is on the shown picture.

Will the 2SK118 alone will be ok to do this task or I'll need a fet which has an incorporated diode as it it shown on the drawing ?

If I need another fet that the 2SK118, what are your recommendations ?

It must be really small with long leads (No SMD)

Thanks
 

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Really, is it now ? :clown:

http://www.onsemi.com/pub_link/Collateral/TF202THC-D.PDF
(mind the boundary dashes)

There's not an abundant choice of low capacitance JFETs, if not SMD (otherwise Sanyo might be an option). And if small size wouldn't be an issue, you'd get away with a K30, same same as K118, but regular/taller TO-92 package.

So are you saying the 2SK53 has an inbuilt G-S resistance as shown for the TF202THC ?

Small signal JFET's read as a "diode" between G and S and G and D with a forward volt drop of around 1.1 volts.
 
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A diode won't bias the FET. As mentioned the diode is an intrinsic property of a junction FET, if that is what they are trying to show. It doesn't bias it though.

You need a gate to source resistor for biasing, maybe of several or many megohms to prevent loading of the electret source.

What sort of FET's do electet mics use ? You can not leave the gate just floating so if the electret source has no DC path you have to bias the FET somehow.
 
The resistors inside the CP-Y are two 30K that comes from the power supply ground and goes to both outputs of the cartridge.

There's no resistors coming from the gate

The two 30K are connected to the ground, not to V+ so that's why I assumed that it was a source follower and not a gain stage.

As you specify that I need a resistor to bias the gate with a source follower, I really don't know what to do now.

Here is what I have but don't know now how it was connected to the FET.
 

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A diode won't bias the FET. As mentioned the diode is an intrinsic property of a junction FET, if that is what they are trying to show. It doesn't bias it though.

You need a gate to source resistor for biasing, maybe of several or many megohms to prevent loading of the electret source.

What sort of FET's do electet mics use ? You can not leave the gate just floating so if the electret source has no DC path you have to bias the FET somehow.

No, the gate voltage equilibrates with the back to back diodes biased by the gate leakage current. Try it some time on the bench, 2SK170 and back to back diodes. For the n'th time there are no resistors in an electret capsule.

Find a 2SK123 data sheet and you will see the operating current in a capsule is outside the Idss range, which allows for the gate floating to a slightly positive voltage (due to drain to gate leakage).

If you don't use a FET designed for capsules, just cut off the drain lead of another FET and connect the gate to source as shown as a diode.
 
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The resistors inside the CP-Y are two 30K that comes from the power supply ground and goes to both outputs of the cartridge.

There's no resistors coming from the gate

The two 30K are connected to the ground, not to V+ so that's why I assumed that it was a source follower and not a gain stage.

As you specify that I need a resistor to bias the gate with a source follower, I really don't know what to do now.

Here is what I have but don't know now how it was connected to the FET.

Looks like a source follower so the diode must go to the source not ground.
 
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No, the gate voltage equilibrates with the back to back diodes biased by the gate leakage current. Try it some time on the bench, 2SK170 and back to back diodes. For the n'th time there are no resistors in an electret capsule.

Find a 2SK123 data sheet and you will see the operating current in a capsule is outside the Idss range, which allows for the gate floating to a slightly positive voltage (due to drain to gate leakage).

If you don't use a FET designed for capsules, just cut off the drain lead of another FET and connect the gate to source as shown as a diode.

Many many thanks for your insight Scott.

Sorry if these are daft questions ;) just trying to expand my knowledge now.
You say "the gate voltage equilibrates with the back to back diodes biased by the gate leakage current. Diodes ? plural, two of. Do you mean the intrinsic "diodes" found in a normal junction FET and if so, that the leakage is both sufficient and presumably equally matched between the two ? Sufficient on their own to be used for biasing. (I am thinking that as the FET is symetrical there must be two diodes.)

Is there any reason why just one diode is shown in the picture and also in the device in Jaccos link.


I appreciate the electret in isolation has no DC path of its own... I have just never heard of FET's being left essentially with the gate OC to self bias if that understanding is correct.

So legarem is going to need a fairly specific FET for this to work.
 
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