"Do MOSFETs have to be matched?" and other assorted newbie questions...

[Ponchus]

Hey everyone
It's been a while since I've posted. I started off strong, got into the whole pedal-building thing thanks to this forum. I built a TS808, a Ross Compressor, a Ross Phaser, a MicroAmp, an Ampeg Scrambler, a LoFo MoFo, a PT80, and a DOD 440 (for my bassist)....everything worked out great, and I took a break from the mess and annoyance of this hobby/addiction.

But now I'm back 

I'm thinking of building ROGs Multi-face, a Phase 45, a Big Muff Pi, an EA Tremolo, and ROGs new Thor pedal. And of course, this brings me to my questions.

Question 1
With the Multi-Face, there are various options listed on ROGs site, using different transistors and caps. I was thinking of going with the "Metal Face" option, which uses two 2N7000's. I believe those are MOSFETS. Do I need to match these?

Question 2
For the Phase 45, I suppose I do need to match the transistors. I will need a matcher to do so (my DMM doesn't have this option built in). I see that Mark M has a perfboard layout of a matcher, available here: http://aronnelson.com/gallery/album77/JFET_Matcher_perf_LAYOUT

Just trying to understand this process. So I plug a 9V battery into the Ground and +9V input, plug the transistor into the holes marked D,S,&G, and the DMM into the two DMM holes. Does it matter which lead of the DMM goes into which hole (is there a positive and negative?). Also, what setting on the DMM? I guess I'm measuring voltage? And then I'm just looking to get two trannys with similar readings right? I hope I'm understanding this correctly.

Question 3
Would any of my other pedals (the ones I've built or the ones I'm going to build) benefit from any matching? Like the Ross Phaser, for example. It sounds great to my ears, but I never matched anything. Can it sound even better if I do so?


Thanks, as always, for all the help you guys provide.

[toneman]

a quick google turned up this----

http://www.susan-parker.co.uk/zeus-mosfet-matching-1.htm



also here---

http://www.passdiy.com/howto/matching.htm

and.....more here.....

http://www.facstaff.bucknell.edu/esantane/movies/aleph-x.html

approx halfway down page where it says:   "mosfet matching"....


I think that's enough for now......

try googling with a friend.....   

May U find a Match   

[Ponchus]

Great, thanks for the fantastic reply and the tutorial on the merits of Google. I'll try buying their stock too. Unfortunately, I'm more of a Yahoo fan.    And also you didn't really answer any of my three questions. The first of which was do I NEED to match the mosfets, not HOW do I match mosfets. Your last link was related to building an amp, but I'm sure those requirements are different than for those of a 9v stompbox builder.

The second question was regarding the use of the jfet test that has been posted here (I believe it's R.G. Keen's design, or one of the other super-geniuses who hang around these parts). I am able to build one since there are PCB layouts and whatnot, but I just didn't understand how to actually USE it once I have it.

The third question was simply asking for tips from the other posters here, 99.5% of which actually know what they're doing. Unlike myself, who simply follows the advice of those that know what they're doing. I was simply asking if there was anything that should be matched (or would benefit from matching) in any of the other builds that I mentioned in my intro paragraph (the past builds that I've successfully...er...built).

I appreciate the sarcasm though,  being an artist in that field myself 

[toneman]

Oh Kay....i'll try again....

1) for amps, the MOSFET output trannys should be matched.
For a stompbox, i don't think it's necessary.  But, It would be interesting to know what the gain characteristics
were for each of eth MOSFETs in each of the stages of good sounding MultiFace or THOR.
I was trying to lead U to discovering if there really *were* differences, and the best way to know is to do.


2)  in a phaser, the jfets *should* be matched so that they have a similar voltage-to-resistance.
this way, each stage is similar to the others, and responds similarily.
Always get the datasheet for the jfet so U can know which pins are  D S & G.
After actually trying  to use the Jfet Matcher, if still puzzled, page R.G.   

3)  can't really answer this, except for jfet phasers.  U can match all U want, and use 1% resistors.
But, the sound is what U are really after.  As Moosapotaus says:  "I tend to like anything that sounds good."

me 2

[petemoore]

With the Multi-Face, there are various options listed on ROGs site, using different transistors and caps. I was thinking of going with the "Metal Face" option, which uses two 2N7000's. I believe those are MOSFETS. Do I need to match these?
   High Gain FF, matched sets of FF transistors...Ge's mostly, Si's you can buy the gain range transistors in batches, pick them by gain, lower gain for Q1 is sometimes said to be preferred, You'll want to try different transistor types and diddle with the bias pot, then the other pots including the volume in your guitar plugged into the MF directly, with the 'right' gains [depending on...]you can get good cleanup of sound at guitar volume..see GEO Technology of the Fuzz Face for explanation.
  In the Jfet phasers, the Jfets are used as variable resistance elements, and need to be closely matched to get phasing...see GEO Jfet Matcher article.

[propadog]

After actually trying  to use the Jfet Matcher, if still puzzled, page R.G.   

I'm going to side with Ponchus on this one. This is more like a clique than a place where people with a common interest but differing levels of knowledge meet.

It has been my experience that unless you are a known demi god, you get brush off sarcastic answers around here. if any answer at all. Some of us are trying to learn and trying to help ourselves. Something a bit more constructive than "google it" or "build it and then when you can't work it out, come back here" would be a bit more helpful.

"After actually trying  to use the Jfet Matcher, if still puzzled, page R.G.   " is not only sarcastic, it's pointless because in my experience RG doesn't respond to emails or PMs. I'm wanting to buy the book he has on Geofex about PCB designs, so I CAN ask fewer questions. I can't get an answer from him. It was hard enough even finding his email address to follow his instructions to email him to get a copy. And I'm sure RG really wants every new person PMing him to find out what to do with it.

I've also got all the stuff for the PCB and the schematic for the matcher, but is it so hard to write one basic paragraph saying "this is what to do"?

Thanks, petemoore, for providing a useful reply. Your help is really appreciated. I will also go and read the articles you suggested.

Toneman, if you ever have a question about VOIP, let me know... I'm sure I can be as helpful as you.

[Dragonfly]

After actually trying  to use the Jfet Matcher, if still puzzled, page R.G.   

I'm going to side with Ponchus on this one. This is more like a clique than a place where people with a common interest but differing levels of knowledge meet.

It has been my experience that unless you are a known demi god, you get brush off sarcastic answers around here. if any answer at all. Some of us are trying to learn and trying to help ourselves. Something a bit more constructive than "google it" or "build it and then when you can't work it out, come back here" would be a bit more helpful.

funny, i havent seen that to be the case here. beginners get their questions answered all the time. often times, its the same questions over and over. 

googling and searching the forums are legitimate answers, as "most" beginners / new forumites ask questions first and search later...not to mention that the the original poster made no indication of having "searched" for the answer.

also, a "hey RG...question for you" type thread on the forum will almost always elicit a reply from him. so yes, paging does work.

"After actually trying  to use the Jfet Matcher, if still puzzled, page R.G.   " is not only sarcastic, it's pointless because in my experience RG doesn't respond to emails or PMs. I'm wanting to buy the book he has on Geofex about PCB designs, so I CAN ask fewer questions. I can't get an answer from him. It was hard enough even finding his email address to follow his instructions to email him to get a copy. And I'm sure RG really wants every new person PMing him to find out what to do with it.

I've also got all the stuff for the PCB and the schematic for the matcher, but is it so hard to write one basic paragraph saying "this is what to do"?

Thanks, petemoore, for providing a useful reply. Your help is really appreciated. I will also go and read the articles you suggested.

Toneman, if you ever have a question about VOIP, let me know... I'm sure I can be as helpful as you.

anyway, pete is usually good with answers

i wouldnt worry about matching the mosfets in a multiface.

as for the jfet matcher, you can probably find the answer by searching the forum which gets you results like this...
http://www.diystompboxes.com/smfforum/index.php?topic=50485.0
http://www.diystompboxes.com/smfforum/index.php?topic=52569.0
http://www.diystompboxes.com/smfforum/index.php?topic=50517.0
http://www.diystompboxes.com/smfforum/index.php?topic=27188.0

i could keep listing the results of the search for "jfet matcher", but these threads ALL explain the ins/outs of how it works...
heres a direct quote from RG in one of the threads...

"Lemme try.

JFETs are depletion devices, which means they normally are "on", no signal required to make them conduct. Like tubes, you have to put a signal on them to turn them off.  With the gate open or shorted to the source, JFETs conduct a current called "Idss", for Current (I) in the drain, with the gate shorted to the source. That is, Vgs=0.

You turn a JFET off with a voltage on the gate negative with respect to the source. A JFET will turn really, really off - giga-ohms worth of off. The voltage between the gate and source that causes drain current to drop to zero is listed as Vgsoff, for "Voltage between gate and source that makes the drain current turn off".

At full on (Vgs=0), the JFET channel between drain and source is resistive. The resistance is also listed on the data sheet as Rdson. Common values are 10 ohms to a few hundred, with the low ones on JFETs designed for switching, the high ones for JFETs designed for RF amplification.

Changing Vgs between 0 and Vgs off changes the channel resistance from Rdson up to essentially infinity. If you want a resistor between Rds on and infinity, chances are you can get it with a JFET.

Phasers need a resistance that wiggles around in that range. Many phasers need a resistance between, say, 1K and 100K. JFETs do this nicely. But they are very non-uniform. Not only do different JFET types have different resistances per Vgs, they vary from one to another within the type.

Case in point. The J201. This is a switching JFET, but it still has a resistive region below pinchoff. (Pinchoff is the drain to source voltage that causes the channel to stay at a fixed current with higher voltages; we have to use JFETs below pinchoff to use them as variable resistors.) The J201 has a Vgsoff spec of about -0.1 to -1.0V ( if i remember right; I don't want to go chasing datasheets right now.) That means that any given J201 **may be** one that goes from 20 ohms Rds with Vgs=0 to fully off with a Vgs of -0.1V. The entire range of resistanct it can sweep is compressed to a 0.1V control signal.  A seemingly identical one **from the same manufacturer** may go from 20 ohms to infinity with a Vgs sweep from 0V to -1.0V, a control range that's ten times larger. This is for supposedly identical devices.

Other JFETs like the prototypical 2N5292 from the P90 have Vgsoff specs of -0.5 to -3.0V. That means the control range from full on to full off is contained within the range of 0 to -0.5V for some devices, 0 to -3.0V for other devices, with most of them in the middle.

My matcher does a single point match. That is, it lets you measure the Vgs voltage that makes a given example of JFET act like a 10K resistor (or whatever resistor you stuff in for Rmatch). That is, it makes the voltage and current in the JFET be equal to the voltage and current for the 10K.

This insures that if you get a quad of JFETs matched this way, you are dead certain that at least one point in the control voltage sweep, they will all be in the desired spot on the resistance curve, and you're dead certain to get some phasing around that spot.

This is how the original 2N5292's were matched for the P90, and probably others. It's not perfect, and here's the fault in it.

A JFET not only has a range of resistance from Rdson to infinity with a range of Vgs, the actual resistance per unit voltage change is not linear. It's not precisely square law, or exponential. This is like pot linearity - changing the pot rotation ( that is, Vgs) a given amount in the low end will NOT give you the same resistance change as the same amount in the high end of the 0 to Vgsoff range. The resistance change per unit control voltage change is not clearly predictable. If you plotted one JFET's Rds versus Vgs, you'd get one curve. If you then plotted a second JFET, you'd get not only another curve, but the curves would not have the same curvature or start and end points, exactly.

A single point matcher ensures that you get sets that have curves that all touch (or nearly so) at one point. What happens away from that point is not known. This is the origin of Mike Irwins' comment that JFETs drop out. Some of them do. They reach the end of their curve and quit when the others are still changing resistance.

The beauty of a single point matcher is that it turns out sets good enough for commercial work ( i.e. the P90) and that non-pros can (sometimes) understand how to do a single point match, as well as the fact that there's about a 50% to 80% yield of quads in a largish batch of same-lot parts. It's fast, it's cheap, it's (sometimes) easy, and it has gotten huge herds of beginners going on something that I still get effects asking me how to do.

If you want to do it *good*, you curve match by matching at more and more points. Here's how:
1. Pick a resistance range. 1K to 100K is a good start.
2. Pick a place in the middle, say, 50K and match a bunch of JFETs there. 3. Throw away any that are not matched well at 50K.
4. Pick another resistance point, say 25K. Match the already-50K-matched parts at 25K. Throw away any that do not match at 25K.
5. Loop back through 4 as many times as you have JFETs and patience for.

Every iteration for another matched point on the resistance-vs-Vgs curve produces a more-closely-matched set of devices. Three points is pretty doggone spectacular IMHO. If you do a good job, you can eventually come up with a set of devices that respond essentially identically. These will produce the most intense phasing sound over the whole range of Vgs that you are using for an LFO. It's about as good as JFETs can get.

And that is the rub. Even **great** JFETs are not perfect. The control voltage sweep is limited and nonlinear (worse yet, nonexponential; exponential is what you want). JFETs vary from unit to unit a lot, and phasers need multiple identical somethings.

So - the matcher matches JFETs at a point where the JFET channel is in the middle of acting like a resistor, and more to the point, acting like a resistor might act in a phaser. It's a single point test. it's good enough for making phasers that work OK-ish when used with good JFETs. J201's are many things, but IMHO, not phaser JFETs. They're too sharp-edged and touchy. The 2N5485 and 2N5292 have always sounded better to me, but as I keep harping on, that's only my ears. Your mileage may vary. People seem to insist that if they get J201s, they're going to use them for everything. Sometimes that even works.

Interestingly,  I don't know that anyone has ever called me on the real flaws in the matcher, those being that it's a DC test, not an AC test and it's at a largish voltage compared to actual signal voltage. I actually designed a MK3 that did an AC test at 100mv of signal. I never put it up because
(a) it is much harder to build
(b) the results seem to be about the same.

Did that help?"

anyway, like i said...people here tend to be quite helpful, but they also want the new people to learn to "help themselves" by "finding" the answers that have been addressed many times over.

best,
  AC

[Ponchus]

Hey all
i really didn't mean to start an argument or a war or anything, I was just looking for some info. In the past, this place has been a huge oasis of help for me and many others. I'm sure it still is, and I do appreciate everyone's help.

I didn't take any offense to Toneman's original response, though it wasn't exactly helpful. After all, if I can simply Google it, why bother coming here at all? Also, with Google (as well as with the searches here, on GeoFX, and in the other forums I frequent), you usually get SOOOOOOOO many results that it's hard to sift through it all. So I asked a question. If you don't have time to respond, then no need to. I'm sure someone else will.

Either way, Toneman's next response WAS helpful, as were Pete Moore's and Dragonfly's. However, Dragonfly cut-n-pasted a long amount of info at the end of his post, and this is typical of WHY I asked a question in the first place. It's TOO good, too technical. I didn't understand a single thing there. I know that ideally, understanding the workings of a transistor will result in me being able to do way more for myself. But for someone who's trying to figure this out as they go along, that wasn't exactly light reading. Also, nowhere in there was a plain-English statement that said "when building circuits, sometimes you'll need to match trasistors. Germanium and jfets should be matched, but MOSFETs do not" or something to that effect. I tried reading through that info and wasn't able to fully understand it. Or partially understand it for that matter.

Dragonfly also stated that it seemed as if I didn't look around before I posted. Nothing could be further from truth. First off, in my first post of this thread, I mentioned that I had already built something like 8 or 9 pedals, including a PT80, a Ross compressor, and a Ross phaser. All of those fall into the intermediate or advanced categories, and I did not get that far by NOT reading. Believe me I spent months on here learning, learning, learning (with everyone's help). Now I'm back, and trying new things. I read through the GEOFX info that everyone points me to (before I was pointed there, btw). It tells you HOW to test jfets, it talks about how to account for leakage in a germanium tranny, but it does not answer the questions that I posted. I searched through the FAQ's here and on GGGs site, as well as ROG for that matter. I also did searches on transistor matching, MOSFET matching, match MOSFET, match transistor, match tranny, do MOSFETs have to be matched, which transistors have to be matched, etc etc. I didn't simply jump right to the "post a question" stage. I think you underestimate how technical some of the language around here can get. It's bewildering for someone who's trying to do this in a "paint by numbers" way.

Anyway, I think I have my answers, so I thank you all, and I hope that no one is mad at anyone else. I do hope that you more advanced people realize that you really need to dumb-down the language a little more when someone specifically tells you that they are a newb though.

It reminds me of the first time I took a formal guitar lesson. I was self taught, and five years into it I learned that a really good jazz guitarist lived on my block. I saught him out and scheduled a lesson. I was a metal guitarist at this point, with interests in classical and jazz. But I was basically a 16 year old metal guitarist who could play pentatonic and natural minor riffs. This guy sits me down and says "so let's talk about the altered ionian mode"....   Needless to say, it was sooo over my head that it was the last time I ever took a lesson. Good player, bad teacher.

[amz-fx]

Question 1
With the Multi-Face, there are various options listed on ROGs site, using different transistors and caps. I was thinking of going with the "Metal Face" option, which uses two 2N7000's. I believe those are MOSFETS. Do I need to match these?

In this particular circuit, you don't have to match them because you can use the 10k trimmer to make up for any variation.  You can make the circuit work well without matching.

Question 2
Just trying to understand this process. So I plug a 9V battery into the Ground and +9V input, plug the transistor into the holes marked D,S,&G, and the DMM into the two DMM holes. Does it matter which lead of the DMM goes into which hole (is there a positive and negative?). Also, what setting on the DMM? I guess I'm measuring voltage? And then I'm just looking to get two trannys with similar readings right? I hope I'm understanding this correctly.

It doesn't really matter which lead of the DMM is connected to which hole. In one direction it will read positive voltages and in the other it will read negative. Just disregard the sign.  You're measuring voltages and looking for two (or more) trannies with similar values.   

Question 3
Would any of my other pedals (the ones I've built or the ones I'm going to build) benefit from any matching? Like the Ross Phaser, for example. It sounds great to my ears, but I never matched anything. Can it sound even better if I do so?

The notch depths on the Ross phaser will be deeper if you match the jfets. This gives a slightly more intense phasing sound.  If you are pleased with it now, don't worry about it.

regards, Jack

[Dragonfly]

Hey all
i really didn't mean to start an argument or a war or anything, I was just looking for some info. In the past, this place has been a huge oasis of help for me and many others. I'm sure it still is, and I do appreciate everyone's help.

I didnt see any arguement

I didn't take any offense to Toneman's original response, though it wasn't exactly helpful.

Thats what *i* thought...*you* didnt seem upset at all. Evidently Propadog took offense to it though.

After all, if I can simply Google it, why bother coming here at all? Also, with Google (as well as with the searches here, on GeoFX, and in the other forums I frequent), you usually get SOOOOOOOO many results that it's hard to sift through it all. So I asked a question. If you don't have time to respond, then no need to. I'm sure someone else will.

I think the term "Googling" was being used in the broader sense..i.e. "searching. I can't really speak for the person who used the term, but thats how "I" took it.

Either way, Toneman's next response WAS helpful, as were Pete Moore's and Dragonfly's. However, Dragonfly cut-n-pasted a long amount of info at the end of his post, and this is typical of WHY I asked a question in the first place. It's TOO good, too technical. I didn't understand a single thing there. I know that ideally, understanding the workings of a transistor will result in me being able to do way more for myself. But for someone who's trying to figure this out as they go along, that wasn't exactly light reading. Also, nowhere in there was a plain-English statement that said "when building circuits, sometimes you'll need to match trasistors. Germanium and jfets should be matched, but MOSFETs do not" or something to that effect. I tried reading through that info and wasn't able to fully understand it. Or partially understand it for that matter.

Sorry, in your original post you mentioned several other projects you'd done, so I assumed (you know what happens when we assume) that RG's response would be "understandable". However, if you "searched" for "jfet matcher" here on the forum, you'll find MANY more answers, most of them easier for a beginner to understand. IIRC, "jfet matcher" yields about 2 pages of resulting threads. I also posted links to a few of those threads.

Dragonfly also stated that it seemed as if I didn't look around before I posted. Nothing could be further from truth.

I never stated that it didnt "seem" like you looked for the answer. I said you "made no indication of having searched for the answer". Two VERY different things. Your original post didn't say "anything" about having "searched" for the answer, thus the reason that Toneman and I suggested it. Both of us have been around here for long enough to realize that 99% of peoples questions have already been answered, time and time again.

First off, in my first post of this thread, I mentioned that I had already built something like 8 or 9 pedals, including a PT80, a Ross compressor, and a Ross phaser. All of those fall into the intermediate or advanced categories, and I did not get that far by NOT reading. Believe me I spent months on here learning, learning, learning (with everyone's help). Now I'm back, and trying new things. I read through the GEOFX info that everyone points me to (before I was pointed there, btw).

Thus the reason I posted RG's answer. It tells "how", and it tells "why".

It tells you HOW to test jfets, it talks about how to account for leakage in a germanium tranny, but it does not answer the questions that I posted.

You asked, among a few other things,  "how" to test Jfets...then you just said that Geofex told you "how" to test Jfets     

I searched through the FAQ's here and on GGGs site, as well as ROG for that matter. I also did searches on transistor matching, MOSFET matching, match MOSFET, match transistor, match tranny, do MOSFETs have to be matched, which transistors have to be matched, etc etc. I didn't simply jump right to the "post a question" stage.

You must not have tried "mosfet" and "multiface" together. That yields quite a few results. I didnt read them all, but I assume that none mention the "need" for matching mosfets in that particular circuit.

I think you underestimate how technical some of the language around here can get. It's bewildering for someone who's trying to do this in a "paint by numbers" way.

Why would you assume that *I* am not the same way ?  I started out with almost ZERO knowledge of electronics, and just searched, experimented, searched, and asked questions till I learned more. I'm still not a "technical" guy. Refer to RG, Mark Hammer, Paul Perry, or any number of other guys for that.

Anyway, I think I have my answers, so I thank you all, and I hope that no one is mad at anyone else. I do hope that you more advanced people realize that you really need to dumb-down the language a little more when someone specifically tells you that they are a newb though.

Nobody is mad. It would be silly to get mad over a stompbox question.  As far as "dumbing down" the language, sometimes thats possible, sometimes its not. It depends on what the question was. Often times things "need" to be explained in a semi-technical manner, though I think that most of the vets around here try their best to keep things as simple as possible. RARELY does any post resemble an electronics coursebook.

As far as the "newb" thing, welcome...

It reminds me of the first time I took a formal guitar lesson. I was self taught, and five years into it I learned that a really good jazz guitarist lived on my block. I saught him out and scheduled a lesson. I was a metal guitarist at this point, with interests in classical and jazz. But I was basically a 16 year old metal guitarist who could play pentatonic and natural minor riffs. This guy sits me down and says "so let's talk about the altered ionian mode"....   Needless to say, it was sooo over my head that it was the last time I ever took a lesson. Good player, bad teacher.

The student *also* needs to be willing to learn. The best teacher in the world cannot teach an unwilling student. Seriously though, all that was said in previous posts was that these questions had been answered before, and you'd find the answers by searching the forum.

Anyway, best of luck in your quest for info.  Have a great...and SAFE ...holiday !

AC

[Dragonfly]

Question 1
With the Multi-Face, there are various options listed on ROGs site, using different transistors and caps. I was thinking of going with the "Metal Face" option, which uses two 2N7000's. I believe those are MOSFETS. Do I need to match these?

No.

Question 2
Just trying to understand this process. So I plug a 9V battery into the Ground and +9V input, plug the transistor into the holes marked D,S,&G, and the DMM into the two DMM holes.

Yes.

Does it matter which lead of the DMM goes into which hole (is there a positive and negative?). Also, what setting on the DMM?

No.

I guess I'm measuring voltage?

Yes.

And then I'm just looking to get two trannys with similar readings right?

Yes.

I hope I'm understanding this correctly.

You are.

Question 3
Would any of my other pedals (the ones I've built or the ones I'm going to build) benefit from any matching?

Maybe, maybe not. Sometimes you get "lucky" by just "throwing the fets in there."

Like the Ross Phaser, for example. It sounds great to my ears, but I never matched anything. Can it sound even better if I do so?

If you're happy with it, then I wouldn't worry about it.

Thanks, as always, for all the help you guys provide.

Youre welcome

[markm]

 

[Ponchus]

Some more excellent responses. Thanks for those! And thanks Dragonfly, you're right in that I wasn't clear in my first post about searching and all that. Either way, it all worked out and you provided some excellent info. Now I can try ordering parts in my hungover state 

Hope you all had a great New Year's, and I will definitely be posting more questions soon about all this, I'm sure. Now I gotta go mix up a Bloody Mary. I should post a request for the best recipe, I'd love to see the debates that leads to lol. "Worcestershire sauce in a bloody mary?! No way!"