matching FETs

[Mark Hammer]

To add to that, the criticality of matching is partly a function of the sort of effect aimed for.  It is well understood that one generally reduces sweep width as sweep speed is increased, and that, conversely much wider sweeps are tolerable when the sweep rate is very slow.  The things that matching affects are MOST audible when one sets a phaser to slow sweeps, since the quality of the "sweep turnaround" is most noticeable under those circumstances.  If what you prefer is subtle gurgley or "spongy" phasing sounds, then matching is not so critical.  If what you like are slow "jet plane" sweeps, then matching starts to acquire importance.

Of course, if you are aiming for a unit that would encompass both possibilities, you plan around the most demanding requirements and match the FETs.

FWIW, I bought myself a wad of 2N5952s from Mouser, threw together one of RG's matcher circuits on perfboard with a decent 3-pin socket to plug the FETs into, and worked out what has to be 6 or 7 matched quartets and even a couple of matched sextets and maybe one octet.  I don't think I have to match anything for a long.  I can't be the only person to have done this.  We should probably start sending each other our used matcher boards.  Or maybe matched sets.

[ghostsauce]

I'd gladly buy 5 matched j201's right now. I've got 15 I've been swapping into my dr boogie this past week and I can't seem to find anything I like.

[solderman]

Thanks for the explanation.

I guess i did not pay that much attention to the subtile parts of the sound. I was so surprised that it worked at all. Then I put the matched ones in and boxed it up.

BTW
Here is my testrig. The pins are for attaching the test clips from the DMM

[fretzburner]

Can we use dual opamp like 4558? what is the technique in measuring the Vgs voltage when it will vary in time? Should we only take note only of the first reading just when we switch on the power supply? My first time here with this FET matching thing.

[R.G.]

Can we use dual opamp like 4558?

Yes. Just use one section, not both.

what is the technique in measuring the Vgs voltage when it will vary in time?

Don't get it hot. the Vgs changes with time primarily when the temperature of the device changes. Your *fingers* are about 86F/30C. They will heat a small semiconductor device several degrees and you can watch this change the readings in many cases. Either wear gloves, use pliers/tweezers to insert and remove the devices.

Should we only take note only of the first reading just when we switch on the power supply?

It's important to do the SAME thing for every device. If you insist on using your fingers to insert the devices to read, hold each one for exactly the same amount of time. Consistency is much more valuable than perfect accuracy.