TILLMAN: HOW TO INCREASE OUTPUT LEVEL?

[Dragonfly]

But there is no quick fix that will give him more gain without changing the sound of it. That's the point.

See my post a few above ...

In a way you're trying to fit a "square peg" into a "round hole. Why, you ask ? Well...here's the reason...My guess is that a BIG part of why he LIKES the Tillman is that the Jfet isn't working too hard...its designed to put out only about 3dB's of gain. Once you start trying to get more gain from it, you push the Jfet harder, which makes the Jfet "sound" different

[frank_p]

I don't know Doug... "quick fix" to me is different than a "permanent fix"...kind of like the guy who puts duct tape around his radiator hose so that he can get back and forth to work a little while longer, instead of replacing the holey radiator hose.

Yeah ! but one simple equation in a three page topic !
It's not like if it was not a quick fixed problem.  And everybody is willing to help...

[JDoyle]

Well,  Jay, it seems that what you say in the second sentence is the opposite from the first...So as long as there are people wnating to learn, your contribution is important - I am telling you that (for now) I just want to walk the easy road (if there's one)...Altough I won't follow your kind suggestions, I thank you so much. 

Sorry - I didn't mean for that to come out directed at you, just an overall sense or feeling in general...

Methinks that if you were to get a multimeter you would be able to come up with some pretty cool stuff if you put your mind to it. Hell you obviously don't mind the part I hate - putting them together, I can't STAND boxing things up, it is so BORING.

I have four BB sized boxes each with 4-6 'holes' for the pots and the jacks/stompswitch/LED/power crap already hooked up. Then when I come up with a circuit I like it takes only a few minutes to clip out the old one and toss in the new one.

With the added advantage of each successive circuit getting quieter as the total length of lead wire gets smaller and smaller with each new circuit! Or so I tell myself.

I end up jamming with my breadboard more than I care to admit.

Seriously, next time you have some spare cash (less and less often for me, I admit) pick up a fairly good multimeter and a breadboard - start with the Tillman you just build, adjust and measure things, and soon you will have your own design.

Regards,

Jay Doyle

[DougH]

Yeah ! but one simple equation in a three page topic !

Haha! Boy, I miss the percolator and series pickup wiring threads about now...

[wampcat1]

What it comes down to is "Does Renegadrian want to solve the problem, or does he want to LEARN HOW to solve the problem?"

I completely understand your point, and do agree. However, I think you are missing the bit in the original post (admittedly, I ignored the whole sans-math/theory bit) that said:

"He asked me if it is possible to have a little more output without changing its tonal characteristics" emphasis added by me

Brian's answer may give more output, but it sure as hell will change the tonal characteristics, for EVERY JFET USED in that circuit.

In hindsight, I should have said:

"Yeah, follow it with a non-inverting opamp stage with an adjustable gain."

But I didn't.

Actually, building another one and putting them in series would probably make a quite nice circuit that went from the boost his customer wants to a distortion he doesn't even know he wants!

actually, we are both partially right, depending how you look at it. I'm done arguing with you about this as you are always right... If don't believe you, all I have to do is ask you and I'm sure you'll tell me.

Your posts on fs.org proves your temperment and I'm not going to play into it, I just simply don't have the time to stroke your ego.

bw

[frank_p]

Yeah ! but one simple equation in a three page topic !

Haha! Boy, I miss the percolator and series pickup wiring threads about now...

Well I think I am going to read on the percolator instead.  Tired of see willing people fight for nothing.

[JDoyle]

Yep... I mentioned that in a post above...what the guy seems to like about the Tillman is that the jfet isn't "driven hard". Reality is that just about anything you do to increase the output is going to drive the jfet harder, thus changing the sound.

Not necessarially. He could optimize the headroom of the stage, which isn't great as is, while keeping the same operating point.

Because the gain of a JFET stage is based upon transconductance and Rd, it is possible to run them less 'hard' and get more gain. Way way off topic here...

I guess he could try putting a couple Tillmans in series, but even that is gonna change the sound.

oh yeah, everything is doubled, the good, like gain, and the bad, like high end freq. response.

Best thing...and not necessarily what Renegadrian wants to do...is design a jfet circuit thats similar to the Tillman that boosts somewhere from 6-9dBs, that way the jfet isn't working itself into overload, but has a bit more output.. (Still gonna sound a little different...just not AS different as driving the jfet hard). Of course that either involves "math", a "breadboard", or "both". 

[Dragonfly]

Yep... I mentioned that in a post above...what the guy seems to like about the Tillman is that the jfet isn't "driven hard". Reality is that just about anything you do to increase the output is going to drive the jfet harder, thus changing the sound.

Not necessarially. He could optimize the headroom of the stage, which isn't great as is, while keeping the same operating point.

Because the gain of a JFET stage is based upon transconductance and Rd, it is possible to run them less 'hard' and get more gain. Way way off topic here...

IMO its exactly "on topic". 

[JDoyle]

I'm done arguing with you about this as you are always right...

THEN PROVE ME WRONG! THAT IS ALL I AM ASKING! There are a number of times when I've been proven wrong and admitted such, happily, because I learned.

I WILL NOT apologize if my defense of my position is more vigorous than your defense of yours.

Your posts on fs.org proves your temperment

Actually, that only proves my temperment toward thieves. But the world does need those who like that sort too, I guess... And when they can step back and say 'see it's only a..' it surely jibes well with your 'it's so simple, all you have to do is...'

It is really funny to me, my online 'personality' here is so out of whack with how I really am. I am extremely chill. Not much ruffles my feathers. I am a nice guy, really. And I am chuckling during these posts, I'm not in a full out rage, sweat pouring down my face. Must be the way my New Englad sarcasm comes off...

But the reason this hobby is so riddled with erronous theories, and guitarists are so quick to jump on 'mojo' as the reason something sounds good, is because people peddle it as 'simple' and easy, despite the fact that what they are spewing is either not 100% correct, and therefore misleading, or absolute and total bullshit.

And I don't want to see something I truly love, my one true hobby that has lasted quite some time, become an undulating morass of pseudo-science, laziness, and plain stupidity.

And I'm not going to let it, without a fight.

Regards,

Jay Doyle

[JDoyle]

IMO its exactly "on topic". 

Save for the equations I would have to use!

[aron]

Here are the Vishay notes. I intend to read them since I have posted hacked FET stages in my pedals.

http://www.vishay.com/fets-small-signal/ssfanp/

There's info in the DIY FAQ too:

http://www.diystompboxes.com/wiki/index.php?title=DIY_FAQ#TRANSISTORS

and in that:

http://www.diystompboxes.com/smfforum/index.php?topic=57219

AN102 directly deals with biasing:

http://www.colorado.edu/physics/phys3330/phys3330_fa05/pdfdocs/AN102FETbiasing.pdf

[drk]

i think that JDoyle does have a point. alot of people don't even try to understand what they're doing, they just want to have that piece of gear cheaper, dont really care about electronics 
of course that, those guys will never be good at building effects, no matter how many pedals they build... 

[StephenGiles]

...and it won't sound that much different from a Rat at the end of the day......and in the morning too!!

[DougH]

What?

No "It's just a @#$%ing fuzz box!" ??

[petemoore]

  Plenty of suggestions to get the breadboard out with.
  I found a few of the Jfet explanations in this thread to be relevant, consice and elemental to the topic.
  If anyone wants to design an optimized for application Jfets amplifier to do...whatever it is Jfets are known to be able to do in that field, a breadboard, a DMM, and some testing /trials /mods sessions applying the information in this tread could produce some A-1 prototypes.
  I never  breadboarded, but instead just built circuits on perfboard using modification friendly build methods.

[JDoyle]

OK. This got under my skin last night:

Equations such as "[(V+)-(Vd)]/(Rd) = Id," are correct, but let's face it - we are guitarists. Let's make it easy enough that my 8 year old could understand without opening a calculator.

Now, lets say that bw's 8 year old daughter is in second grade, the grade I was in at 8 (I got lucky being born in 1974 - take any year and I can tell you what grade I was in...simply by looking at the last digit of the year. 1980? Kindergarten. 1986? Sixth. etc.).

This is what I found from a quick google search: http://www.ixl.com/math/grade/second/

Now, no, I admit, no algebra, no division with decimals, but pretty damn close. In fact, I was a bit stunned at the level a 2nd grader is at, mathematically at least. They deal with graphs and charts; you know, those things you can find on a DATASHEET???

PLUS:

In the equation [(V+)-(Vd)]/(Rd) = Id

WE ALREADY KNOW EVERY VALUE ON THE LEFT HAND SIDE OF THE EQUATION!!!!

We know V+ because it is, and has been pretty much forever, the 9V battery.

We know Vd = 4.5V because that the standard output bias.

We know Rd = 6800 because it was on the damn schematic.

I'll go out on a limb here and say everyone can do the math between the brackets in their heads. Even a drummer.

After that, oh boy does it get tough, 4.5 divided by 6800. Yikes. That IS scary... [/sarcasm]

Seriously, if someone building an effect is too put upon to do that kind of simple math, the kind of math they do in their heads every night after a gig when they split the take, they need to 'man up' as Doug said.

Unbelieveable that that one equation was jumped on as being TOO COMPLEX FOR GUITARISTS. And downright insulting to guitarists too. Sure, if it was the diode equation, or the JFET transfer curve if the triode region, I understand the argument - those are complex formulas, though still solvable.

Because I honestly think that a bright 8 year old COULD do that equation on a scratch pad, if someone explained the algebra part (you can't expect an 8 year old to grasp that) OR substituted in the numbers for him/her. They would most likely get stuck at a final fraction (4.5/6800 or 4¹/₂/6800), according to that study guide I found, but still, an 8 year old COULD do it... Long division apparently comes in 3rd grade, so I guess once you hit 9, you are too smart to be a guitarist.

But it's too much work for Mr. Wampler. Hope someone else does his taxes...

Not to mention, do we really all want to be shooting for a level of design equivalent to an 8 year old's mathematical ability? We obviously can do better, so, shouldn't we?

Or should we honestly start to worry about schematics carrying cooties?

Regards,

Jay Doyle

[frank_p]

  Plenty of suggestions to get the breadboard out with.
  I found a few of the Jfet explanations in this thread to be relevant, consice and elemental to the topic.
  If anyone wants to design an optimized for application Jfets amplifier to do...whatever it is Jfets are known to be able to do in that field, a breadboard, a DMM, and some testing /trials /mods sessions applying the information in this tread could produce some A-1 prototypes.
  I never  breadboarded, but instead just built circuits on perfboard using modification friendly build methods.

Exactly Pete, it's helpfull for working, learning and taking measures.  Plus if you are beginning with FETs its the kind of circuit to concentrate on.

The problem is that it was not what was asked in the first place.
The thing that is wanted is only "the answer" or "the concept" that will permit to have more volume with the same charachteristics.

Everybody is willing to do the small work (breadboarding, measuring, make some protos, etc...).  But once it's done, some just want the answer.

It's the typical behaviour that a lot of the guys don't like here, because it gives the bad feeling of that "cloning your things" issue, instead of lets make some road together...

I should shut my mouth because I don't like arguing...
So continue to work but what will probably happen, is what is happening all the time:
paint by numbers behaviour and claiming that it's the stompbox that "you made".
Everything is "normal" here.  Even more, it's what is happening all the time.

That is sad because a lot of people that could help others to make better "electronicians" think they should rather shut their mouth or they will get stuck in an endless infernal spiral.
So everybody that want to learn something or help others will have the feeling that they must stay in the "corner".

Even the beginners think they can't start a technical topic otherwise they will be covered with prey birds even before they grow an off to have claws.

It's like the ones that claim that they do informatics because they boot Windows
and use the internet... 

Lets face it we have a problem.

P.S.  You MUST have a multi-meter, we don't have the natural ability to see the electrons going around...

[Gus]

I googled Tillman preamp.  Find the source
http://www.till.com/articles/GuitarPreamp/

It was designed for about 3db gain this is written in the introduction

In the "A Note about FETS" part he recommends trying a few fets and measuring the drain voltage.

So D. Tillman fet gain stage was a design for low gain, lower output resistance(6.8K) and > 1meg input resistance.

Like I posted on page 2 of this thread try a 47K drain resistor and adjust the source resistor for the operating points you want and bypass it with say a 100uf 16VDC electro(I like to use a signal generator set to triangle wave and a scope to adjust bias) 

[wampcat1]

OK. This got under my skin last night:

Equations such as "[(V+)-(Vd)]/(Rd) = Id," are correct, but let's face it - we are guitarists. Let's make it easy enough that my 8 year old could understand without opening a calculator.

Now, lets say that bw's 8 year old daughter is in second grade, the grade I was in at 8 (I got lucky being born in 1974 - take any year and I can tell you what grade I was in...simply by looking at the last digit of the year. 1980? Kindergarten. 1986? Sixth. etc.).

But it's too much work for Mr. Wampler. Hope someone else does his taxes...

Not to mention, do we really all want to be shooting for a level of design equivalent to an 8 year old's mathematical ability? We obviously can do better, so, shouldn't we?

Or should we honestly start to worry about schematics carrying cooties?

Regards,

Jay Doyle

Dude, you need some counseling... let it go! 
I honestly can't believe that this stupid thread is consuming your thoughts. Wow... wish that was the only problem I had to worry about!

No, it's not too much work for me, thanks for the assumption though.

If it's not too much to ask, please pm me your telephone # so we can take this off the forum and get this straightened out since this is turning into a personal attack against me.
bw

[gez]

Gentlemen, select your weapons:





4 pages and the OP's question has been answered...hasn't it?