Layout fof JFET Matcher anyone

[Austin73]

Just read RG 's JFET  matcher with great interest but just wondered if anyone had a vero layout of it as I'm lazy tonight.

Sorry in advance

Aus

[Seljer]

theres on in the gallery http://aronnelson.com/gallery/album75/Fet_Matcher_1

[Austin73]

Cheers Just what i needed

Aus

[zjokka]

hi all,

sorry but could somebody explain me what's to be matched in jfets.
you wire up this one and measure the voltage? but what is that voltage?
might matched fets solve the problems i'm having with the fet based amp simulations?

thanks beforehand
zj

[Thomas P.]

the voltage between gate and source.

[R.G.]

sorry but could somebody explain me what's to be matched in jfets.you wire up this one and measure the voltage? but what is that voltage?

This matcher measures the voltage between gate and source which makes the drain-source channel resistance match a 10K resistor for DC current flow.

You can match many things in JFETs. The most important ones for use in phaser circuits are the drain to source resistance that results from a specific gate-to-source voltage. That lets you use several JFETs as resistors and have the resistances change together with the same signals on the gate.

might matched fets solve the problems i'm having with the fet based amp simulations?

It's unlikely. That requires a different set of issues. The maximum current that a JFET will conduct is called "Idss", which stands for the current (I) that flows from drain to source when the gate to source is shorted. The transconductance also matters. This is the amount of drain current which flows per volt of change on the gate.

[zjokka]

thanks RG,

but where then does this great difference between the same type of jfets manifest itself? some people don't use them, because of that. since I learned that I'm always suspecting the difference between fets to be the problem in my builds.

more and more i learn you can always bias them, if not your wiring is wrong.

see this thread