TILLMAN: HOW TO INCREASE OUTPUT LEVEL?

[dschwartz]

Brian, thank you for your reply - you understood the case - I am a builder with a straight approach, no multimeter reading sessions, no math equations - just build from a given an verified layout.
You fully and clearly understood and answered my need, see, I don't want/need to learn equations or other stuff like that (at least for now, but I never liked that approach...) - so your hints are so precious and easy to follow - that's what I'll do!!!

damn!, i was just about to explain the harmonic content with fourier differential equations!! and using schroedinger to calculate the probability to find a suitable fet from a batch..



well, really, i was going to recommend the same as brian..
i made a fet booster "the tuna boost" in a tuna can in 10 minutes for a friend.. just like the tillman, but a trimpot instead of  Rdrain and a 10uF cap parallel to R source (and made Rsource 1k)..coupled the output, filtered the b+ and added a variable high pass filter (100pF cap parallel to a 50k pot in series with signal) to make it work as a treble booster as well.. it worked beautiful..fet boosters dont have a ton of volume boost, but they sound really great..

[wampcat1]

Brian, thank you for your reply - you understood the case - I am a builder with a straight approach, no multimeter reading sessions, no math equations - just build from a given an verified layout.
You fully and clearly understood and answered my need, see, I don't want/need to learn equations or other stuff like that (at least for now, but I never liked that approach...) - so your hints are so precious and easy to follow - that's what I'll do!!!

You aren't alone - most of us prefer the 'non-engineer' approach

glad to help -
Brian

[Gus]

Brian  Did you write a book about modding effects and you post use a drain trim?
 Fets math for a circuit like this is not hard.  Simple ohms law will get you in the "ballpark" for drain resistor values.

 Whats your output Z/drive and Id with using a drain trim?   Drain trims are a hack not a design.
What is the range of resistor values for low noise with jfets?  It might not be what people have posted in this thread.

Want more gain with a unselected j201 use a 47K drain(about .1ma drain current) and a 10K to 25K trim pot in the source adjust the trim for the drain voltage you want.  Next use a fixed resistor(s) to match the pot resistance setting and solder the fixed resistor(s) in place of the trim pot with a electro cap of a big enough value as a bypass(RC time constant stuff).  A 201 has a low noise range of about 100k to 1Gig look at an106.  Adjust the gate to ground for the loading that sounds best for your guitar you have a wide range.

To do it right measure the IDSS (9 VDC battery and a meter set to ma)  that will help pick the drain R you can use.

Read the app notes they are good.

[wampcat1]

Brian  Did you write a book about modding effects and you post use a drain trim?
 Fets math for a circuit like this is not hard.  Simple ohms law will get you in the "ballpark" for drain resistor values.

Again, you are forgetting, this fellow just wanted the damn thing to work, be louder, and doesn't give a damn about the technical side. Do you HONESTLY think that most guitar players care about ohms law or WANT to know about ohms law?

 Whats your output Z/drive and Id with using a drain trim?   Drain trims are a hack not a design.

Again - just make it simple. Most guitar players don't care about z/drive or ID. They just want "connect this and this and this".

What is the range of resistor values for low noise with jfets?  It might not be what people have posted in this thread.

Want more gain with a unselected j201 use a 47K drain(about .1ma drain current) and a 10K to 25K trim pot in the source adjust the trim for the drain voltage you want.  Next use a fixed resistor(s) to match the pot resistance setting and solder the fixed resistor(s) in place of the trim pot with a electro cap of a big enough value as a bypass(RC time constant stuff).  A 201 has a low noise range of about 100k to 1Gig look at an106.  Adjust the gate to ground for the loading that sounds best for your guitar you have a wide range.

Again, do you really think the average guitar player cares about rc time constant?

To do it right measure the IDSS (9 VDC battery and a meter set to ma)  that will help pick the drain R you can use.

Seriously. 

Read the app notes they are good.

Or, just follow my quick and easy instructions if you just want the damn thing to work without having to study app notes for hours.

No offense Gus, but I noticed there was a need for "laymens" diy stuff years ago. That's why I wrote the books, because so many people on here go overboard with explaining alot of correct theory, yet most of us guitar players just want a better sound, the technical side is boring. Nothing wrong with that. So, no- I don't go into math of any sort in the books. It's all paint by numbers type stuff. It's done very well for me since about 2004 or so, which makes me think there is a WHOLE lot of people who feel that way.
bw

[R.G.]

I think what you're saying Brian is that there are always people who don't want to be confused with the facts, right? 

As the man said, no one ever went broke underestimating the taste of the American public.

[JHS]

Raising the gain in the FET-stage is not a good idea 'cos it alters the basic in this stage too.

R. Keeley published a schem for a FET-booster some time ago in pdf-format with a FET front and a MPSA18 backbone for gain.
You can find the circuit as a sample in nearly every electronic kompendium. The MSPA18 snipplet in the PDF can be added to any simple FET-boost like the ROG stuff and others.

JHS

[JDoyle]

or, said another way, use a trimpot instead of the 6.8k to find out what value would work best, or even leave the trim pot in.

NO!!!!

That is the WORST POSSIBLE advice! A trim on the drain GUARENTEES that unless two people end up with JFETs having the EXACT SAME properties EVERYONE who builds the circuit will have COMPLETELY DIFFERENT results.

Sorry to hurt your brain, but I've got to use an equation to prove this...

The gain of a common source JFET stage with the source resistance bypassed is (essentially): Av = gm * Rd

So your advice is to adjust one of the components of the above equation until they get what they want??? Convenient. But absolutely wrong. By doing that each individual builder will end up with their own unique outcome. Great for them, moreso if they like it and there aren't sound samples to compare what they have against what the circuit is supposed to sound like, but useless for everyone else.

I don't understand why such a simple question would get such non-laymans term answers, but this is all simple stuff and the OP probably doesn't care about idss or anything like that.

BECAUSE THEY ARE NOT SIMPLE QUESTIONS.

If it was so 'simple' to build JFET amplifiers why don't we see them in more commercial equipment???

It IS really simple to design a JFET amplifier if you know the properties of the JFET you are going to use; a simple way of finding this information out Gus presented and you then mocked.

If you are building for a wide range of JFETs, such as in a commercial setting, or say, if you publish a schematic to the internet and the people who find it expect to have their hands held by someone else while they build it - but don't hold their hand too hard or try to get them to actually learn how to do it on their own, that will just end in a temper tantrum - the results are NOT going to be happy ones. As we see here.

And yes, we ARE all guitarists. Which by definition means that we have already learned, whether we know it or not, numerous things much more complex than the simple algebra I mentioned in my post above. Every time you set up a guitar you deal with harmonic theory; play a chord? You just applied Cartesian Geometry. It's OK to expect a competent guitarist to know the difference between the Phrygian and the Dorian modes (set theory, by the way) but NOT OK to ask them to do some simple algebra???

Please.

Let's make it easy enough that my 8 year old could understand without opening a calculator.

HELL NO!!! I want to make it a damn SCIENCE instead of the frigging witchcraft/mojo/'it hurts my brain to think like that' BS we mostly have here now.

8 year olds believe in the tooth fairy, and ignorant guitarists believe in mojo.

Neither of which exist.

But of course convincing people that it IS simple helps sell your book, doesn't it?

Nothing like a vested interest to solidify an opinion.

He wants more volume out of a given schem. Easy.

Easy huh?

Now, please define 'volume' for me. Because you have increased (or decreased, depending on where that trim ends up) the GAIN, so while it may have increased volume, it also could have increased distortion through either clipping OR squashing, lowered the upper -3dB point due to Miller capacitance, etc. Assuming the bias worked out in a way that the trim ended up GREATER than the original value. If it didn't, you just helped him LOWER that gain AND the volume. Great work.

Not to mention what if he was already getting 7V p-p OUT with a Vgs of 2V and a fresh 9V battery, and STILL wanted more, what do you do then? Oh wait - you wouldn't have a damn clue because save for the 'fresh 9V battery' bit, the rest of that statement would have required the OP to actually KNOW how to find the other values, and also required YOU to actually USE THEM! The horror!!! But again, equations are banned, so you BOTH are just simply screwed.

It is attitudes like this, your book, build your own clone sites, and the over-abundance of bootweek pedal makers that not only makes everyone with a soldering iron think that they too can do that, but more importantly:

IT IS WHY WE STILL SEE THE SAME THREE CIRCUITS REHEATED OVER AND OVER AND THEN SERVED UP AS THE NEXT BEST SOUP AVAILABLE.

I'd rather it change so that we could see, call me crazy here, a NEW circuit every once in a while; but then, that wouldn't sell your book would it???

Regards,

Jay Doyle

[Gus]

Yes on the same NS app note pages that the minibooster came from are FET BJT compound amps

[JDoyle]

All right, you got me 
You wrote that my tillman shouldn't work!? I built it as is in the layout I posted above...And it works very good! So I am surely missing something...I should read again what you wrote, but first my need is to give some more output (volume) to the good working circuit I built following the layout above.

As I said, if you got lucky and used a JFET/J201 with an Idss greater than 0.66mA it most definitely will work - sort of.

BUT - you ARE getting distortion. A lot of it actually. One half of the output signal is either clipped or squashed significantly - at most it has 1/2 the headroom as the other swing.

I'm glad you like it and that it does work. But it ain't 'clean' and getting more 'volume' isn't as easy as bw would have you think.

If there ever comes a time when you decide you want to try to build your own circuits from scratch, not just modify something from a schem you found online, you will find yourself going through the exact same equations I did above.

I do apologize if I confused you, but I really WAS trying to help - and not just you, but everyone who reads this thread.

Hell - at least you didn't ask 'What's the BEST JFET???'  

Regards,

Jay Doyle

[frank_p]

It's good sometimes to have meat with your potatoes.
Thanks Jay.

P.S.: "We" don't need to swallow the bone, but meat is good once in a while...

[wampcat1]

I think what you're saying Brian is that there are always people who don't want to be confused with the facts, right? 

As the man said, no one ever went broke underestimating the taste of the American public.

hehe! sorta.... actually more saying that the details aren't always important... some guys like fast food type diy 

[wampcat1]

or, said another way, use a trimpot instead of the 6.8k to find out what value would work best, or even leave the trim pot in.

NO!!!!

That is the WORST POSSIBLE advice! A trim on the drain GUARENTEES that unless two people end up with JFETs having the EXACT SAME properties EVERYONE who builds the circuit will have COMPLETELY DIFFERENT results.

Sorry to hurt your brain, but I've got to use an equation to prove this...

The gain of a common source JFET stage with the source resistance bypassed is (essentially): Av = gm * Rd

So your advice is to adjust one of the components of the above equation until they get what they want??? Convenient. But absolutely wrong. By doing that each individual builder will end up with their own unique outcome. Great for them, moreso if they like it and there aren't sound samples to compare what they have against what the circuit is supposed to sound like, but useless for everyone else.

I don't understand why such a simple question would get such non-laymans term answers, but this is all simple stuff and the OP probably doesn't care about idss or anything like that.

BECAUSE THEY ARE NOT SIMPLE QUESTIONS.

If it was so 'simple' to build JFET amplifiers why don't we see them in more commercial equipment???

It IS really simple to design a JFET amplifier if you know the properties of the JFET you are going to use; a simple way of finding this information out Gus presented and you then mocked.

If you are building for a wide range of JFETs, such as in a commercial setting, or say, if you publish a schematic to the internet and the people who find it expect to have their hands held by someone else while they build it - but don't hold their hand too hard or try to get them to actually learn how to do it on their own, that will just end in a temper tantrum - the results are NOT going to be happy ones. As we see here.

And yes, we ARE all guitarists. Which by definition means that we have already learned, whether we know it or not, numerous things much more complex than the simple algebra I mentioned in my post above. Every time you set up a guitar you deal with harmonic theory; play a chord? You just applied Cartesian Geometry. It's OK to expect a competent guitarist to know the difference between the Phrygian and the Dorian modes (set theory, by the way) but NOT OK to ask them to do some simple algebra???

Please.

Let's make it easy enough that my 8 year old could understand without opening a calculator.

HELL NO!!! I want to make it a damn SCIENCE instead of the frigging witchcraft/mojo/'it hurts my brain to think like that' BS we mostly have here now.

8 year olds believe in the tooth fairy, and ignorant guitarists believe in mojo.

Neither of which exist.

But of course convincing people that it IS simple helps sell your book, doesn't it?

Nothing like a vested interest to solidify an opinion.

He wants more volume out of a given schem. Easy.

Easy huh?

Now, please define 'volume' for me. Because you have increased (or decreased, depending on where that trim ends up) the GAIN, so while it may have increased volume, it also could have increased distortion through either clipping OR squashing, lowered the upper -3dB point due to Miller capacitance, etc. Assuming the bias worked out in a way that the trim ended up GREATER than the original value. If it didn't, you just helped him LOWER that gain AND the volume. Great work.

Not to mention what if he was already getting 7V p-p OUT with a Vgs of 2V and a fresh 9V battery, and STILL wanted more, what do you do then? Oh wait - you wouldn't have a damn clue because save for the 'fresh 9V battery' bit, the rest of that statement would have required the OP to actually KNOW how to find the other values, and also required YOU to actually USE THEM! The horror!!! But again, equations are banned, so you BOTH are just simply screwed.

It is attitudes like this, your book, build your own clone sites, and the over-abundance of bootweek pedal makers that not only makes everyone with a soldering iron think that they too can do that, but more importantly:

IT IS WHY WE STILL SEE THE SAME THREE CIRCUITS REHEATED OVER AND OVER AND THEN SERVED UP AS THE NEXT BEST SOUP AVAILABLE.

I'd rather it change so that we could see, call me crazy here, a NEW circuit every once in a while; but then, that wouldn't sell your book would it???

Regards,

Jay Doyle

wow... someone has some issues sounds like...


Usually you just delete your posts after you calm down, but that's ok - I won't take offense.
I didn't mean offense to gus or anyone else either, but ummm... yep it pretty much is simple for the OP's purpose. If you are clipping, reduce the signal going in, i.e. volume control before the jfet.

you are forgetting one important thing though, the same as alot of the "old timers" feel... not everyone wants to learn this stuff. They just want a working circuit, and if they are having a problem they just want it fixed. like some guitarists, they may have no desire to learn theory. believe it or not, there actually are a ton of guitar players who would smoke me or you on a good day and don't know the difference between a mixolidian and a penatonic blues. Or at least, they don't know it by name, but they know it when they hear it.

The reason for all the byoc type sites is simple... it's profitable! It's profitable because there are ALOT more people that don't want the theory and details compared to the ones that DO want the theory and details.

Sorta like cooking... if i like to cook a good hamburger on the grill, i don't necessarily care about how my grill works, how heat is produced from it, or what part of the cow my hamburger comes from. I just want a hamburger.

bw

[Renegadrian]

Seems I started a nice topic...still I'm becoming a bit hungry (soup, hamburgers...)
Even DIYers need to turn off the iron and have a meal!!! 

[DougH]

This thread cracks me up...

Someone asks how to get more volume out of a circuit and some people oblige- take 5 minutes and read an app note, take another 5 and actually put a pencil on a piece of paper for a simple Ohm's law calculation. This is how you optimize your circuit for your particular JFET to get the best performance. [Belushi Animal House voice= ON] But Nooooo...We can't do that!...That's too hard!...Boo-Hoo!! [Belushi Animal House voice= OFF] ( ) And we end up with the same hacky bullsh*t drain trimmer suggestions- over and over...

Bottom line is JFETs are not consistent and are not easy to work with for audio. If they were you'd see a lot more of them used this way. And this has been mentioned on this forum a gazillion times.

If you are going to publish a schematic for a JFET circuit that more than one person is going to use, don't use parlor tricks like drain trimmers, because each build will sound different and some won't work at all. I.e. the results will be very inconsistent.

If you don't want to do any reading and/or actually learn anything new, the best hack is to put a 100k on the drain, put a trimmer on the source and bypass that with a big cap. I've experimented with this and it works fairly consistently, much better than the drain trimmer solution. Of course if you want to do source circuit shelving EQ there are other tricks  you will have to play. There's no free lunch, as they say.

And no, generally speaking, electronics cannot be dumbed down for 8 year olds. Sooner or later you just have to man up...

[Renegadrian]

Would you then suggest this 8-year-old to try different j201s??? Shall I find big differences amongst them???

[JDoyle]

wow... someone has some issues sounds like...

Yup - with those that hinder any sort of advancement in this field by espousing an 'it's so simple' point of view. That view only serves to continue the long dry road of 'yet another TS/Dist+/FF with cap changes' we have been seeing. I mean, I have zero repect for Mike Fuller as a designer, but damn, at least he tried something NEW with the boost function on his fulldrive. He TRIED to progress.

I didn't mean offense to gus or anyone else either, but ummm... yep it pretty much is simple for the OP's purpose. If you are clipping, reduce the signal going in, i.e. volume control before the jfet.

Ummm... Simple does NOT mean that it is RIGHT.

Forget the added noise and sub-optimal S/N ratio aftermath of reducing the signal BEFORE the amplifier with a pot. (to avoid that you would probably say, 'just use a lower value pot' and neglect to mention the effect of that pot's loading of the previous stage, the fact that if it is too low it would actually INCREASE the noise of a JFET stage... but then, that wouldn't be a 'simple' answer would it?)

It just means it's simple. To quote Einstein 'Make everything as simple as possible, but not simpler.' - who, I'm going to go out on a limb here and say, was smarter than either of us, combined - unfortunately, you've made the answer 'simpler', and therefore WRONG.

Did you even understand my point? It could end up that your drain trim is a LOWER value than that in the schematic - and you have REDUCED the volume. ESPECIALLY if the OP couldn't find a J201. Or his J201 was actually a missorted J202?

What would you do then? Find another trim and hope for the best???

Seriously, what would be YOUR answer in that case? Be sure to keep it as simple as you say...

you are forgetting one important thing though, the same as alot of the "old timers" feel... not everyone wants to learn this stuff. They just want a working circuit, and if they are having a problem they just want it fixed. like some guitarists, they may have no desire to learn theory. believe it or not, there actually are a ton of guitar players who would smoke me or you on a good day and don't know the difference between a mixolidian and a penatonic blues. Or at least, they don't know it by name, but they know it when they hear it.

So we are supposed to aim for the lowest common denominator? We never challenge the existing myths? We never strive for anything new? To understand anything?

So you are saying that it is better to stagnate and get it done than to actually learn anything and progress?

Bullsh!t.

I may be alone in believing this, but THERE IS SO MUCH UNTAPPED POTENTIAL IN THIS FIELD - ESPECIALLY IN THE AREA OF DISTORTION.

But as long as there is a 'simple' answer, few will strive to find out the 'right' answer, and in the process discover something new.

The reason for all the byoc type sites is simple... it's profitable! It's profitable because there are ALOT more people that don't want the theory and details compared to the ones that DO want the theory and details.

I agree wholeheartedly. But in that case stick to another paint-by-numbers BBS for your questions and know that when someone takes the time to explain to you the process of CORRECTLY doing something, it is EXTREMELY rude to dismiss it outright, and only serves to shine a light on the 'dismissers' ignorance when they post the WRONG answer - no matter how simple it is.

Sorta like cooking... if i like to cook a good hamburger on the grill, i don't necessarily care about how my grill works, how heat is produced from it, or what part of the cow my hamburger comes from. I just want a hamburger.

No. It isn't even 'sorta' like cooking. Your analogy would be right on if all you had when you wanted that hamburger was a schematic and parts for the grill and a live, chewing cud, cow standing before you. Remember, the OP is building from scratch.

If I was building a gas grill from scratch (which I would NEVER do, by the way, I'm a charcoal man all the way) with nothing but a schematic, I would certainly want the CORRECT answer to any questions I had, not the SIMPLEST. Simply for self preservation reasons.

In this case someone found a schematic and was pretty much building something from scratch and wanted to know how to get 'more volume' WHILE KEEPING THE SAME OVERALL RESPONSE. You told them how to get more volume (maybe, if the Gods were in a good mood and let the OP pick a high Idss J201, OOPS! I used some math!!!) while most definitley screwing up every other variable in the process. To me - that doesn't answer the OP's questions, and certainly NOT CORRECTLY, no matter HOW SIMPLE your answer is.

However, if you had an answer to the simplest way to slaughter the cow, as long as the first step was actually killing it, I'd probably go with you on that...

But, unfortunately, building something using semiconductors from scratch, isn't as easy as slaughtering an animal (if step one is killing it, if it's not, it can be CONSIDERABLY more difficult. )

And again, nothing like a vested interest to solidify an opinion,

Regards,

Jay Doyle

[Dragonfly]

Fet Principles and Circuits, by Ray Marston

DOWNLOAD LINK

There are 4 downloads of good, easy to understand info that should help you in the future. It's a nice set of articles that balances "technical" and "easy to understand".

[JDoyle]

Would you then suggest this 8-year-old to try different j201s??? Shall I find big differences amongst them???

I think it's time you need to open a textbook and do some math...

Or - build a Minibooster over at AMZ, about as much gain from one JFET stage as you can get, it will bias up right, and you'll never have to worry about it again... Unless you want something changed...

For the record, way way way back in the 'old site' archives are several posts by R.G. trying to help an ignorant me build a common source JFET stage from scratch. In the end, he quit answering my 'problem de jeur', as he put it, and just laid out the way to do it for me and anyone else reading.

Simply the best advice I have ever gotten from this board - this stuff ISN'T easy and it takes knowledge to get a result that you want.

However, if you just want to 'build and go' with good volume/tone, I think the Minibooster might be the route for you...

Regards,

Jay Doyle

[JDoyle]

Fet Principles and Circuits, by Ray Marston

DOWNLOAD LINK

There are 4 downloads of good, easy to understand info that should help you in the future. It's a nice set of articles that balances "technical" and "easy to understand".

Great call!

Erno Borbely has some great articles on his site:

www.borbelyaudio.com

And the Siliconix App notes are classics.

[frank_p]

Would you then suggest this 8-year-old to try different j201s??? Shall I find big differences amongst them???

There is also a paper at GEO I think about FETs measurment.