jfet matcher -Quest for markm - Im clueless-also looking for layout

[jimbob]

http://aronnelson.com/gallery/album76/JFET_Matcher_LAYOUT

I decided I would go ahead and build yet another phaser (phase 90) and need to match the fets. I came across this and looks great. But- How does it work? I can see where the transistor would be placed and 2 leads of the dmm, but what about the grounds? Anything connect to that/those? I assume the neg lead of the battery and the posit goes to the +9v. Anything else I need to know to match these damned things? What do you set the dmm to while testing?

Im also looking for a Phase 90. The one at Tonepad doesnt seem to be available

Maybe Ill just change my forum name from jimbob to clueless

[ulysses]

hey jimbob

yeah you only need to connect the ground to the neg lead on your battery

i would not use a battery myself as the voltage will drop as you test your fets and give you slightly differnt results. use a wall wart and dc jack.

if you are testing 500 fets at a time then you may end up with very different results that differ enough to throw them out. then end up having to recheck everything.

http://aronnelson.com/gallery/album75/Fet_Matcher_1 is the one i built and it works very well. its a bit easier as its on vero.

cheers
ulysses

[ulysses]

depending on the fets you are matching you will need to set your dmm to the voltage that is the on/off switch voltage of the fets

so for 5458's like i used i set my dmm to under 2000mv and it gave results in the 700-1170mv range.

i found that if they were a couple of mv out then they would still phase ie, 832mv and 834mv would work.

cheers
ulysses

[markm]

i would not use a battery myself as the voltage will drop as you test your fets and give you slightly differnt results. use a wall wart and dc jack.

cheers
ulysses

Nahhh!
I use a battery and the difference is minimal at the most.
It's not an exact science, it's gets you close enough that whatever you need matched JFETs for, it should work fine.

[ulysses]

depends how many you are matching

i was matching 500 and the results did slip by 5-10mv by the end of it.

enough to make me think that there were less matches that there actually were.

cheers
ulysses

[markm]

i was matching 500 and the results did slip by 5-10mv by the end of it.


cheers
ulysses

Now that's a different story!!