Hiya fellows, I'm going to do some jfet matching for some 2SJ103, 2SK170, etc. I would like to know if the below schematic is appropriate for my purpose?
Hiya fellows, I'm going to do some jfet matching for some 2SJ103, 2SK170, etc. I would like to know if the below schematic is appropriate for my purpose?
I can't comment on this matcher because I've never used it. But Anatech, one of the moderators here, designed a pretty good transistor matching jig that also matches jfets. I have used it with great satisfaction. I believe Anatech posted it in a thread somewhere on DIYAudio. You can try searching for it or just PM Anatech.
The only advice I can give you is to match your transistors at the current and temperature you will be using them at and allow sufficient time for the transistors to reach a settled temperature. Do a rough match first and catalog the results then a second accurate match.
This work for me.
Cheers,
David.
Good suggestions. I'd add one of the National temp sense IC's to your setup. A touch of Heatsink compound between the sensor and the test device. Take your readings at the same temp on each device you test. I had to teach that trick to the Racal Dana engineers who were hand selecting Transistor arrays for best offset drift on an exotic function generator. It works.
Doc
Doc
Hi loop9.
It's Anatech. If you search for anand's you find much.
Good suggestion thaumaturge. I like the idea of the thermal sensor.
Anatech's matcher is a differential circuit. Two transistor are being matched at once.
I keep the transistors against one another so they are thermally coupled and let them self heat at room temperature.
Another aspect of matching is that each transistor may have a different current-temperature curve. Therefore it maybe beneficial to test them over a range of currents and temperatures rather than just one point. This insures the transistors will stay matched dynamically.
I have done point matching to 0.1% with anatech's jig.
One suggestion from Anatech is to take one of those foam packing peanuts, hollow it out a bit and place it over the transistors under test. This jig is so sensitive that even a small room temperature change upsets the differential balance.
Cheers,
David.
It's Anatech. If you search for anand's you find much.
Good suggestion thaumaturge. I like the idea of the thermal sensor.
Anatech's matcher is a differential circuit. Two transistor are being matched at once.
I keep the transistors against one another so they are thermally coupled and let them self heat at room temperature.
Another aspect of matching is that each transistor may have a different current-temperature curve. Therefore it maybe beneficial to test them over a range of currents and temperatures rather than just one point. This insures the transistors will stay matched dynamically.
I have done point matching to 0.1% with anatech's jig.
One suggestion from Anatech is to take one of those foam packing peanuts, hollow it out a bit and place it over the transistors under test. This jig is so sensitive that even a small room temperature change upsets the differential balance.
Cheers,
David.
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Jfet matcher.
Hi Zero Cool,
I think it was in Fred's link for the Adcom power amp repair. Everybody was in on that one.
I'll see if I can find it. Better yet how about I just post the JPG of the jig.
I built this on a single perf board with the circuits back to back and used dip sockets and header sockets to plug the transistor into.
For the different polarities I just flip the board around.
The current set resistors are an example. Other values can be chosen for other currents. I used a header to connect the resistors and made the connection using one of more of those shunt jumpers you'd find on a hard drive.
Cheers,
David.
Hi Zero Cool,
I think it was in Fred's link for the Adcom power amp repair. Everybody was in on that one.
I'll see if I can find it. Better yet how about I just post the JPG of the jig.
I built this on a single perf board with the circuits back to back and used dip sockets and header sockets to plug the transistor into.
For the different polarities I just flip the board around.
The current set resistors are an example. Other values can be chosen for other currents. I used a header to connect the resistors and made the connection using one of more of those shunt jumpers you'd find on a hard drive.
Cheers,
David.
Attachments
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Jfet matcher pics
Hi All,
Here are a couple of pics of my matcher.
The 10K and 100 ohm resistors need to be hand matched.
The nominal value is not as important
Cheers,
David.
Hi All,
Here are a couple of pics of my matcher.
The 10K and 100 ohm resistors need to be hand matched.
The nominal value is not as important
Cheers,
David.
Attachments
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Long ago National Semiconductor published an app note for building an FET curve tracer to work with a 'scope. It you have a scope it's a worthwhile thing to build, though it only does small signal FETs. It gives a single curve, not a family like the Tek and other tracers do. I don't think the circuit is on-line anywhere, at least I didn't find it, but I can probably dig it out and scan it if anybody's interested.
Hi Conrad,
Was it anything like this?
Curve Tracers
We used this in school for demonstration a very long time ago.
David.
Was it anything like this?
Curve Tracers
We used this in school for demonstration a very long time ago.
David.
Attachments
Ian Fritz paper was just linked to today here
http://www.diyaudio.com/forums/analogue-source/200674-matching-2n4401.html#post2786490
I think this BJT matching method transfers to jFETs.
http://www.diyaudio.com/forums/analogue-source/200674-matching-2n4401.html#post2786490
I think this BJT matching method transfers to jFETs.
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Here's the National circuit. For educational purposes, so hopefully it falls under fair use. I've built this and it works well.
Ian Fritz matching jig works with jFETs.
I changed the Vds diode to an LED for a higher Vdg of ~ 1.8V instead of 0.6Vdg
I reduced the pair of 100k to 10k+-0.05% to allow for much higher drain currents in k170bl.
These source resistors could go much lower yet, maybe down to 1k+-0.05% if you require matching at 5 to 10mA.
DUT takes a bit of time to settle to the same temp as REF.
I changed the Vds diode to an LED for a higher Vdg of ~ 1.8V instead of 0.6Vdg
I reduced the pair of 100k to 10k+-0.05% to allow for much higher drain currents in k170bl.
These source resistors could go much lower yet, maybe down to 1k+-0.05% if you require matching at 5 to 10mA.
DUT takes a bit of time to settle to the same temp as REF.
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