More JFET questions

[electricstorm]

I asked about the J201 in another post regarding the Chunk Chunk and am satisfied with the answers I received. Now, I need clarification on JFETS in general but I'll use the J201 in this post. I am not that familiar with JFETS as I have not used them before in a project.

I ordered 20 J201's from Smallbear and 10 from Mammoth. The one's from Smallbear are Fairchild devices and the one's from Mammoth are IRC devices (manufactured by Fairchild and IRC). My first question:

Can you mix devices from different manufacturers in peddals? In my usual dealings with electronics, it is OK to mix them except in rare instances or critical circuits. But I'm not sure in audio circuits.

My second question is in regards to matching. How close do they have to be matched? I have used the JFET matcher circuit from JMK and grouped them to what I think are close matches. Here's what I have from each manufacturer (single listings didn't appear to match closely with anything, the othere are grouped to what I believe to be close matches):

The specs say that Vgs(off) should be between -0.3mv to -1.5v. As you can see, they are all on the low side, not close to the minimum spec. at all.

Fairchild (readings are in mV and are negative voltages)

.033

.068, .074

.095, .099, .099

.187, .191, .191, .193, .194

.123, .129

.137

.156

.209, .211, .212

.251, .259 (these may be too far apart to be a match)


IRC (readings are same criteria as Fairchild above)

.110

.127, .132

.146

.160, .163, .165, .165

.176

.196

I need to know if any of these can be more groupings and if I am grouping them correctly. I do know I need to order more than 20 or 30 to get more matched sets. I had not read the articles on matching when I originally ordered.

One last question. Do I want to use the highest value matched sets (or for that matter, highest value single devices if ony one is needed)?

Any clarification would be greatly appreciated.

Jim

[Vallhagen]

If that really is millivolts (you say it twice in your post, so i guess it's not a typo?), then i guess something is wrong in your test setup.

jfets are known to be widely speced, and out of range, but from a batch of 20+, there should be at least a few that are within spec.

...as always, i could be wrong. Cheers:)

[midwayfair]

You can mix manufacturers. You're unlikely to find something varying wildly between manufacturers. NOS might different -- some older versions of components are different, particularly transistors. Depending on when a circuit was first made, there COULD be something funny going on with the transistors.

FETs do not have to be matched in any circuit except a phaser.

I agree that something weird seems to be happening with your matching circuit. If you were just using your multimenter, try breadboarding one of the simple FET matchers instead. I tested 30+ 2N5457 not too long ago and they almost all fell between .74 and .78. J201s were a little higher but I only tested about 10.

[electricstorm]

Thanks guys. I'll have to recheck my test circuit. I am using the JFET Matcher from JMK Pedals (I think that is Josh's circuit). The DMM was set to the 2v scale and the above readings was what I got.

Jon, I'll breadboard the test circuit and try again. The test circuit I used was on perf board. I could have made an error in wiring it.    I'll let you know later.

There's a phaser circuit I wanted to try out and that's why I was trying to match the JFETs. I probably won't use the J201's for that but I wanted to at least get familiar with matching them. If the readings above are correct (not saying they are at this point), do I have them matched close enough?

Jim

[electricstorm]

I breadboarded the JFET matcher circuit and re-checked the J201's. Basically, I got the same readings as above within a mV or two. So either my JFETS are wacky or the JEFET matcher is screwy. I'm pretty sure I wired the circuit correctly and tested them according to the GEO article on matching JFETS.

Can anyone shed some light on this at all? They all seem to be way below the specs in the datasheet (Vgs(off) -0.3v to -1.5v).

Thanks,

Jim