# What's All This Matching Stuff About? - part 1



## jubal81 (Nov 25, 2020)

Chuck, you've got a real knack for explaining these things in a succinct way pedal builders can understand.

As far as selecting JFETs for phasers, I've seen a lot of hand-wringing over using specific part numbers. Is there any attribute other than |Vp| that matters? Is there a 'goldilocks zone' for |Vp| for phasers?


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## Chuck D. Bones (Nov 25, 2020)

Specific part numbers are not important, getting Vp in a zone that's compatible with the LFO and bias circuit is important.  That zone depends on the specific Phase-Shifter circuit.  Keen's circuit measures the Vgs required to achieve a specific Rds, 10K in this example.  Having that and a Vp that's not too small is good enough.  Ideally, we want to match Rds vs Vgs along the entire range of Vgs.  We only need two points to do that, so in theory you could mix part numbers if you matched Vgs at two different Rds values.  At the two extreme ends of the Vgs range, we have Vp and Idss.  If you matched those, then the Rds vs. Vgs curve matches along the entire range.


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## cooder (Nov 25, 2020)

And as we poor buggers can't pay you royalties or so we can pay you tribute by naming you *Sir* Chuck.... sort of royalties...
Cheers for that again!

So as I'm looking to build a propolis what is a recommended and easy enough procedure to measure and match Vbe?
Also: what matching would you suggest for the eqd Tentacles / Squidward?


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## cooder (Nov 25, 2020)

... and while I'm at it: which parts would be critical to get right and matched in the Foxx Tone Machine / Fuzzy Foxx?


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## Chuck D. Bones (Nov 25, 2020)

You ask a lotta questions for someone from New Zealand 

Vbe matching: use a real transistor tester if you have one, otherwise measure base to emitter with the diode setting on your DMM.  Get 'em as close as you can, preferably better than ±25mV. 

Squidward & Tone Machine: match the octave diodes for Vf, same as above.  Use 1% resistors.


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## cooder (Nov 25, 2020)

Chuck D. Bones said:


> You ask a lotta questions for someone from New Zealand
> 
> Vbe matching: use a real transistor tester if you have one, otherwise measure base to emitter with the diode setting on your DMM.  Get 'em as close as you can, preferably better than ±25mV.
> 
> Squidward & Tone Machine: match the octave diodes for Vf, same as above.  Use 1% resistors.


... well I'm born in Germany if that explains things a bit more.... .

Thanks for reply, I don't have a _real _transistor tester, just a cheapy ebay component tester. Will try with DMM and the cheapie tester and see how far it gets me.

And I'm sure I will have a lot more questions for you as we go.... thanks for spreading the wisdom.


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## Chuck D. Bones (Nov 25, 2020)

I use a $20 Chinese component tester with very good results.  I have compared the numbers against a curve tracer and they are plenty accurate for what we do.





There's a PF5102 in the socket.  These guys don't measure Idss or Vp, just Id at some arbitrary Vp.  Good for health checking JFETs, rough sorting and verifying pinout, but not very useful for matching.  They are very good for testing germanium transistors because they measure Iceo & HFE accurately.

With a nickname like Cooder, I woulda guessed y'all was from Alabama  .


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## Nostradoomus (Nov 25, 2020)

Yep I use one of those too...and a Peak DCA55 just to be sure


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## cooder (Nov 25, 2020)

Great, that's encouraging!



Nostradoomus said:


> Yep I use one of those too...and a Peak DCA55 just to be sure


How close are the cheapie tester and the Peak DCA 55 with results, have you compared them? Cheers


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## Chuck D. Bones (Nov 25, 2020)

The DCA55 doesn't measure inductance or capacitance, BTW.


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## Nostradoomus (Nov 25, 2020)

Chuck D. Bones said:


> The DCA55 doesn't measure inductance or capacitance, BTW.



No it doesn’t, I was surprised when I threw an inductor into the cheapo tester and it gave me anything at all! Haha


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## Chuck D. Bones (Nov 25, 2020)

It won't measure pickup inductance because the resistance is so high, but it will measure 500mH wah inductors no problem.

I just measured the primary inductance of a Mouser 42TM013 transformer I bought from Small Bear.  1.96H end-to-end, 132mH either end to the center-tap.  The 132mH reading is plausible, but 1.96H is about 4x too high. This thing has issues measuring some inductors.  

It's fun to test 2-color LEDs with it.  You get a mini light show.


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## Nostradoomus (Nov 25, 2020)

Yeah I had a few 100mH radial inductors lying around so I threw em in there just to see.


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## cooder (Nov 26, 2020)

For testing GE transistors I use the R. G, Keen method, do you gusy recommend that as well? Should be fairly good way I guess with his expertise?!
The Chinese component tester seems off for those and doesn't get the leakage properly if I'm not mistaken.


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## Chuck D. Bones (Nov 26, 2020)

I have measured Ge transistors on my Chinese tester and a curve tracer and they agree, so do not be too quick to discount the Chinese tester's accuracy.  Do you have a link to Keen's method?


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## cooder (Nov 26, 2020)

Chuck D. Bones said:


> I have measured Ge transistors on my Chinese tester and a curve tracer and they agree, so do not be too quick to discount the Chinese tester's accuracy.  Do you have a link to Keen's method?


On the geofex page 'technology of the fuzz face' he describes his method of measuring with a DMM under the header 'picking transistor for the fuzz face. What does Sir Chuck think of it?
http://www.geofex.com/

Edit: here's a better link. http://www.geofex.com/Article_Folders/ffselect.htm


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## Chuck D. Bones (Nov 26, 2020)

Seen that method before.  Steve Daniels describes the same method on his Small Bear how-to pages.  It makes a proper measurement of leakage (Iceo) and DC gain (HFE).  I expect the Chinese tester does something similar.


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## Chas Grant (Nov 26, 2020)

Thanks Chuck for another killer installment of The Boneyard! The information you put in these is Top Notch!

As for matching Ge transistors, I have used Steve Daniels method, I matched 2 Chinese Ge transistors out of a lot of them that someone gave to me. I then put them on a breadboard and cherry picked the bias resistors to get the proper voltages on the transistors, soldered them up and boxed it. It is a darn fine fuzz face if I do say so. I have a fuzz face with a matched set I bought. I compared the two, no difference really between them. They both sound great and track each other throughout the level and gain range. So Steve's method works really well.
   I've also done this with Si NPN, but didn't worry about the leakage current, and it works just as well. To me a matched set and cherry picked bias resistors sounds better than using the trimmer pot for the bias voltages, but that's just my opinion


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## cooder (Nov 26, 2020)

Chas Grant said:


> Thanks Chuck for another killer installment of The Boneyard! The information you put in these is Top Notch!
> 
> As for matching Ge transistors, I have used Steve Daniels method, I matched 2 Chinese Ge transistors out of a lot of them that someone gave to me. I then put them on a breadboard and cherry picked the bias resistors to get the proper voltages on the transistors, soldered them up and boxed it. It is a darn fine fuzz face if I do say so. I have a fuzz face with a matched set I bought. I compared the two, no difference really between them. They both sound great and track each other throughout the level and gain range. So Steve's method works really well.
> I've also done this with Si NPN, but didn't worry about the leakage current, and it works just as well. To me a matched set and cherry picked bias resistors sounds better than using the trimmer pot for the bias voltages, but that's just my opinion


Great thanks! So what is a good practical methodology to cherry pick the resistor values and what are we aiming for?

I know, more and more questions....


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## Chuck D. Bones (Nov 26, 2020)

I was saving that for Part 2.  I'm sure there will be plenty of discussion on the topic of biasing a Fuzz Face because it is very subjective.  The trivial answer is you build a Fuzz Factory and turn knobs until you get the sound you like.


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## Chas Grant (Nov 26, 2020)

Chuck D. Bones said:


> I was saving that for Part 2.  I'm sure there will be plenty of discussion on the topic of biasing a Fuzz Face because it is very subjective.  The trivial answer is you build a Fuzz Factory and turn knobs until you get the sound you like.


That would be the easy way, I will let that be part 2 then! So I guess @cooder will have to wait?


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## cooder (Nov 26, 2020)

Oh yeah more suspense... and I can wait...
.... kind of... twiddling thumbs.... 
Many thanks guys! 
Cool place to hang out, that Boneyard.


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## Jbanks (Nov 29, 2020)

Chuck D. Bones said:


> People talk about matching transistors, but what do they mean?
> 
> There are a few instances in pedal circuits where matching transistor parameters to each other or to circuit requirements is essential for proper performance.
> 
> ...


Chuck,

amazing job explaining all this to all of us less literate builders out there. ?

I know you were mostly discussing matching phasor for transistors but for SMD components like a JFET201, will I still need to test them or are they robotically built to enough spec to be matched because it’s SMD?

thanks in advance!


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## Chuck D. Bones (Nov 29, 2020)

Thanks, Man.

J201s, whether they are SMD or TO-92, are the same die, tested to the same specs at the factory.  Like all JFETs, the Vp and Idss limits are pretty loose.  What happens to them after they leave the factory depends on the vendor.  Even an in-spec J201 will not work in every pedal.  Whether they need to be selected or matched depends on the specific circuit.  The Calamity is very picky about J201s.  Most of the ones you buy will probably NOT work in that pedal.  I have not seen any phase-shifters with J201s in them, I suspect it's because their Vp is so small.  I doubt that PedalPCB screens or sorts their J201s.  They may spot check a few to make sure they're getting a good batch.  If you're building pedals with JFETs in them, your best bet is to buy a lot more than you need, test them all and sort them by which pedal needs which specific Vp range.  Cross you fingers and hope you get a decent yield.  That's what the professional builders do, the smart ones anyway.  You way wonder, what do the pros do with the JFETs that they can't use?  They might sell them to a dealer at a discount who then tries to unload them on eBay.

I test all of my JFETs before installing them because it's easy, I know what I want for each circuit and it avoids unpleasant surprises.

One more thing... it's really not necessary to quote one of my articles in its entirety (or at all) in your response.  My shit is pretty long-winded.  I'm not bitching or criticizing, just offering some friendly advice.


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## cooder (Nov 29, 2020)

More great advice there, cheers!
How would we know which pedal likes or needs a specific Vp range?
Do you test smd jfets with the chinese component tester and how many have you dropped being lost forever in the carpet?


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## Chuck D. Bones (Nov 29, 2020)

cooder said:


> How would we know which pedal likes or needs a specific Vp range?


You have to analyze the circuit.



cooder said:


> Do you test smd jfets with the chinese component tester and how many have you dropped being lost forever in the carpet?


I have tested a few, mounted on the little adapter boards.  So far, none have been eaten by the carpet.  I feed it a steady diet of trimmed leads and bits of wire insulation.


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## Kroars (Nov 29, 2020)

Chuck D. Bones said:


> People talk about matching transistors, but what do they mean?
> 
> There are a few instances in pedal circuits where matching transistor parameters to each other or to circuit requirements is essential for proper performance.
> 
> ...





Chuck D. Bones said:


> People talk about matching transistors, but what do they mean?
> 
> There are a few instances in pedal circuits where matching transistor parameters to each other or to circuit requirements is essential for proper performance.
> 
> ...


Love reading your articles man.  Please keep em coming!


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## Chuck D. Bones (Nov 29, 2020)

Thanks!


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## peccary (Nov 18, 2021)

Hello Chuck,

I had a question about the Mofeta: it calls for four 2N5457's - should these be matched in this circuit? I've not seen matching mentioned with it, but I wanted to be sure.

Also, just a point of clarification: Are Vgs(off) and Vp the same thing? I have a lot of sorting to do and want to make sure that I don't have to do it twice, thanks!


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## Chuck D. Bones (Nov 18, 2021)

Matching the JFETs is not necessary.  Just make sure that Q4's Idss is at least 5.5mA.  Alternatively, you could bump R10 up to 10K, then Idss can be as low as 1.8mA.

Vp and Vgs,off are the same thing.  Us lazy people would rather type two characters instead of seven.

It _might _make a difference if Q5 and Q6 are matched for Vbe and HFE, but I would not obsess over it.

*[CORRECTION]*
I had previously stated that 2N5246 is rated for 15V max.  That is incorrect, it is rated for 30V max.
If you use 2N5246s, be aware that they are rated for 15V max.  It's a conservative rating and they should be good for at least 20V at room temp.  The safe thing to do is keep the drain voltages below 15V by starting with the BIAS trimmers at maximum resistance and adjusting from there.  Not trying to scare you, just doing my due diligence.


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## fig (Nov 18, 2021)

Well, he should have plenty


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## peccary (Nov 18, 2021)

Chuck D. Bones said:


> Matching the JFETs is not necessary.  Just make sure that Q4's Idss is at least 5.5mA.  Alternatively, you could bump R10 up to 10K, then Idss can be as low as 1.8mA.
> 
> Vp and Vgs,off are the same thing.  Us lazy people would rather type two characters instead of seven.
> 
> ...


Thanks for the reply, Dave. 

I have a good number of 5457's from the previous group order that I am planning on using for the Mofeta, but I had considered trying the 5246's to see what the difference might be, so I appreciate the heads-up!


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