JFET Auto-Biasing

[tca]

So has anyone else figured out how to auto-bias JFETs for use in Fetzer Valve type circuits? By auto-biasing I mean leveling the playing field for all JFETs by using simple fixed value parts, thus eliminating the need for transistor sorting, trimmers, or additional active devices. I'm thinking that from a manufacturing standpoint this would save an enormous amount of time and money.

I've never thought of that in that way, i.e, so simply stated. But I *can* find a way to do it.

Do you remember the value of the source resistor for the Fetzer valve circuits: Rs = 0.83 * |Vp| / Idss? Actually it is Rs = 2^(-1/4) * |Vp| / Idss

I do like puzzles.

Cheers.

P.S. (edit)

And yes, I will post it here

[ggedamed]

[...]
I'm sorry but am I not allowed to start a conversation on this forum?
[...]

A conversation should have at least a topic.

I'm guessing English is your second language....

[...]


You obviously don't work in this industry, and apparently you don't have anything intelligent to add to the conversation either.
[...]

You didn't add anything intelligent to your own conversation, so why would anyone else?
And who gives a rat's ass about working in the industry? The name of this forum is DIYStompboxes.com.

Now I'm certain English is your second language.

Oh, my, you gave away my cover. Care to enlighten me about the special meaning of English being my second language? In short sentences, please, I'm obviously well below the level of your intelligent conversation.

[aethertransit]

it's hard to start a dialogue with someone who keeps insulting everyone and refusing to consider alternative viewpoints. food for thought.

You are absolutely full of yourself. Not to mention the fact that you started heckling me before I could get an intelligent conversation going. Nice job.

I was one of the first people to openly discuss this with you, but then you went on your rant, and my opinion of the nature of the thread and intentions of the author were modified as a result.

Life gets a little more surreal every day..

I'm sorry Captain Kangaroo but can you quote this "rant" that I supposedly went on? Yes you were openly discussing it with me and all was well until Merlin decided to open his big mouth and become accusatory, at which point you followed suit. I'm done arguing with you about how this all played out, as the record of it is right here in black and white, and you've shown your true colors. Now if you don't mind, I've got a mountains of PMs to answer from people who want to carry on a real conversation. Have a special day.

[diydave]

I have this book from Phillips, it's from around 1976, and in it the problem off the jfet is explained. Be it somewhat short.
But the principal is the same as given in the Vishay note: an external constant bias-voltage to the Gate, and a biasresistor to get the Vgs.
The idea was, and apparentely is, to level out the differences between fets.

Haven't tried it yet, but seems very interesting.
And apparentely not all that new.

But for now, I'll stick to my fetcalculator. Low resistorcount, no need for drain-trimmers and managable frequencyresponse.

[tca]

So has anyone else figured out how to auto-bias JFETs for use in Fetzer Valve type circuits? By auto-biasing I mean leveling the playing field for all JFETs by using simple fixed value parts, thus eliminating the need for transistor sorting, trimmers, or additional active devices. I'm thinking that from a manufacturing standpoint this would save an enormous amount of time and money.

As stated it can not be done. The JFET parameters in the Fetzer Valve are crucial to get the correct frequency response and the relative amplitudes of the different harmonics.  The contradiction is clearly stated:  "auto-biasing I mean leveling the playing field for all JFETs". Danyuk's paper on this "Triode Emulator" clearly shows that the exponent n=3/2 strongly depends on  JFET parameters.

The only way of getting an almost auto-biasing mechanism is using something like this (and even then...):



ALAS it is not the Fetzer way (although with a similar spirit).

Ref.:
- http://www.scribd.com/doc/65330169/Triode-Emulator-by-Dimitri-Danyuk
- http://www.radiomuseum.org/forum/the_trioderizer_a_solid_state_triode.html

Cheers.

P.S.(edit)

Unless you reveal your schematic, and show what it really stands for, there is nothing more to add.

[Bill Mountain]

1.  I believe it was Gus who designed a JFET boost using a bipolar power supply but I can't find the link.  Personally, I like to use JFETs at higher than normal voltages to help minimize the differences.

2.  I understand why you don't want to share your design.  There are people out there who can mobilize at the speed of lightning.  The problem is, is that those aren't the people who respond to these threads.  I don't see any regular posters on here that are out to steal other people's designs.  There are some professional designers and builders here who share plenty of their work.  What they don't share are the circuits they want to keep to themselves.  R.G. has said as much himself.  I see no problem with that but this forum is about DIY and sharing so most threads are doing just that.  Your thread though clumsy at first is a fine topic but we've been discussing it for ages and the chances are slim that anything new will get presented.  If I wanted to confirm the novelty of my design but didn't want to share it, I would simply PM a member you respect with enough experience to offer real help.  I've done that in the past (thanks PRR!) and it was more helpful than if I had posted a thread.  There are reasons some forums have rules against teasing.  I know you're excited to talk about your idea but if no one knows what it is then it's hard to have a meaningful discussion.

3.  The ability to design and build pedals comes second to marketing and business savvy.  The moment your design is out for public consumption is the moment you'll have to say goodbye to exclusivity.  If the next guy is a better salesman your f'd.

4.  Good luck!

[merlinb]

2.  I understand why you don't want to share your design.  There are people out there who can mobilize at the speed of lightning.  

Can someone please explain who are these people waiting to 'steal' ideas off some poxy amateur hobby forum? About poxy little stompboxes for kiddies to play wannabe rockstar with? You make it sound like industrial espionage on a corporate scale, whereas I suspect it's just some schmo making a couple of dozen clones in a shed... Am I wrong?

[Bill Mountain]

2.  I understand why you don't want to share your design.  There are people out there who can mobilize at the speed of lightning.  

Can someone please explain who are these people waiting to 'steal' ideas off some poxy amateur hobby forum? About poxy little stompboxes for kiddies to play wannabe rockstar with? You make it sound like industrial espionage on a corporate scale, whereas I suspect it's just some schmo making a couple of dozen clones in a shed... Am I wrong?

What I'm saying is that the OP wants to build a unique exclusive design.  I doubt there are big time players snooping these threads but there are builders like us who will go ahead and build a new circuit when they see it.  A percentage of those may try to sell a few and a percentage of that percentage may try claim originality.  It's a perceived fear and its perpetuated by the fact that the other forum has to explain it's only an investigative site time and time again.

[deadastronaut]

i don't even have a shed...

my pedals are poxy though..

[Bill Mountain]

I think to sum up what I was saying is that if you don't want anything in the public domain (for any reason) then don't bring it up.

[tca]

^ I always think of this quote when threads like this appear:

"What we cannot speak about we must pass over in silence." -- Ludwig Wittgenstein, Tractatus Logico-Philosophicus

Cheers.

[Bill Mountain]

^ I always think of this quote when threads like this appear:

"What we cannot speak about we must pass over in silence." -- Ludwig Wittgenstein, Tractatus Logico-Philosophicus

Cheers.

Why is it that people with fancy names can always say things better than me?

[aron]

This thread has very little info in it and all from regular posters. It has degraded in quality.