Two JFET Amps

[adamasd]

While digging through my hard drive I stumbled apon this,

It looks like something from PRR, but I can not find the original post. I have been staring at these for abit and can't really figure the point, is it just two way to the same thing or do they have some advantages and disadvantages other then the 2db difference in gain and increased parts count.

The bias in the second on is 0.3volts since the gate is floated up to 1.5?

What would the usefulness of doing this be.

R5 is just to keep the ground reference and to keep the 1.5 volts from just going to ground?

Thanks,
adam

 

[rafafredd]

If I recall, it´s from NYDave. He will probably be here for answering these questions.

 

[adamasd]

Your right, it was NYD, maybe I can dig up the old post now.

 

[adamasd]

Yup, The JFET Brain Teaser, I remember this one now.

http://www.groupdiy.com/index.php?topic=11065&highlight=jfet

Now just to sort it out

Ok, I got it, simple enough. Thanks for the pointer to NYD

Oh I remember this quite well, this circuit was beginnings of NYDs booster pedal which I made and still use. Its all coming back

 

[PRR]

> like something from PRR

I don't do Courier font.

Nor put line-drawings in JPG format.

 

[Guest]

It may be Ok to loose some sound quality (bias depends on signal level and time) when in mass production (less dependence on parameters of each particular FET), but for DIY the first schematic would be preferable.

 

[adamasd]

I don't do Courier font.

Nor put line-drawings in JPG format.

Sans-serif and duotone gifs, It should never have even crossed my mind that it came from you.

but for DIY the first schematic would be preferable.

In areas were quality of sound is most important I would agree with you. But in things like a guitar booster as Dave used this circuit for, the second may cost a quarter more, but it will get the job done with no need to tweaking the bias for each stage or swapping fets. They both seem to have their place in DIY.

 

[Guest]

[quote author="adamasd"]

In areas were quality of sound is most important I would agree with you. But in things like a guitar booster as Dave used this circuit for, the second may cost a quarter more, but it will get the job done with no need to tweaking the bias for each stage or swapping fets. They both seem to have their place in DIY.[/quote]

Such variable bias means "farting sound", no good for a guitar. A small dose means "rubber sound", again no good...

 

[NewYorkDave]

I don't do Courier font.

Nor put line-drawings in JPG format.

I probably chose JPG because the Twin-X server wouldn't accept GIF uploads and I hadn't discovered PNG yet.

Adamasd, I'm glad you like the booster pedal. I still use mine all the time. Here's the circuit for anyone else who wants to try it:

PDF

The high-ish output impedance isn't a problem when using it in front of a typical guitar amp input. But you can always add an emitter-follower output buffer if so inclined.

 

[mr coffee]

Wavebourn,

Such variable bias means "farting sound", no good for a guitar. A small dose means "rubber sound", again no good...

Umm, could you say more about what you mean by "farting sound" and "rubber sound"?

I hear these terms thrown around but I have never been clear what they mean. And when I hear "elastic sound or feel" the guitarist uttering these phrases seems (from their accompanying attitude) to be seeing this as a sonic plus.

Since a "rubber sound" is "no good", I take it rubber sound does not equal elastic?

Thanx

 

[Guest]

I would be glad to meet that guitarist to explore that elastic sound. I honestly do not know what it means, probably absence of some specific transistor artefacts?
As for "rubber" and "farting" I believe he can demonstrate you how they sound.