Matching Jfets

[ildar]

Matching Jfets-How do (can) I use my multimeter to do this?

[petemoore]

The Jfet matching fixture at GEO
 Or there's an 'improved' Jfet matcher somewhere...

[Mark F]

Go to R.G.'s site(GEOFEX) the link is at the top of this page. Build his JFET Matching circuit and you can match your JFETS. If you mean can you match JFETS with only a DMM and nothing else I don;t think you can.

[ildar]

Went to Geofex and found the schem for the jfet matcher. Just one thing I don't recognize-the triangular part of the schem coming from the pictured DMM. What is that?

[cd]

Went to Geofex and found the schem for the jfet matcher. Just one thing I don't recognize-the triangular part of the schem coming from the pictured DMM. What is that?

It's an opamp.

[ildar]

If it's an op-amp, why are there only 4 pins accounted for?

[MartyMart]

When the standard triangle op-amp symbol is used in a schematic, the numbers relate to the "used" connections in the circuit, any which are missing, are therefore not required/connected.
Cheers,Marty.

[Gringo]

Hey Al, check this out:



Hope it helps.

[ildar]

Thanks, Pablo!
So, assuming U1 is the opamp (IC1?), it looks as if only 2 pins are connected. Is that right?

[Lonestarjohnny]

Nice layout, Paul,      
Lonestarjohnny

[ildar]

So, is it just 2 pins connected on the op amp?

[Gringo]

Pins 2, 3, 4, 6, 7 are used.

Pin 7 -> 9v
Pin 4 -> Gnd

Pin 2 -> fet source, etc
Pin 3 -> "lower" test point, etc
Pin 6 -> fet gate, "upper" test point, etc

[ildar]

Right, I see that now. I just wasn't looking at the pcb very closely. Sometimes things have to be spelled out for me...   :lol:

[littlegreiger]

I have a question: What IC do I use? Like would a TL071 work?

[Hal]

yea it looks like any single opamp with standard pinouts will work there (like the tl071)

[Gringo]

Yes, about any standard single opamp should work.

[Fret Wire]

Pablo, is that a new layout?

[Gringo]

No, it's not a new one. I once had a small piece of board that i wanted to use, so i built a fet matcher. The whole thing is available at my site, but it's such a simble thing to perf...