New JFET guitar preamp project

[jazzpeter65]

Dimitri;

It's not my intension to use the 2N5457 FET in my preamp.

First I tryed BF245, but they sounded a little dull and lifeless to me. I had a few 2N3819 lying around and they sounded much better. Much more brilliance and no grain.

Try to look at their data and tell me what you think.

http://www.ligo.caltech.edu/~vsanni/ph5/Datasheets/FET/2N3819.pdf

- Peter

 

[jazzpeter65]

Shunt Regulated Push-pull gainstage as a output buffer?

Dimitri,

The guitar pre I'm working on is basically two (inverting) gain stages and one source follower/impedance converter.

I'm wondering if the gain comming from it will be enough to drive a poweramp? Will it have the nessary voltage swing and current output to drive it?

Or would adding a FET buffer be better?

I just found an interesting FET guitar pre at: http://www.sugardas.lt/~igoramps/grass_preamp.htm

I looks like it has a SRPP circuit at the output.

Jack Ormann utilizes this circuit in his mini-booster (took the idea from an old National appnote. See: http://www.generalguitargadgets.com/fet_an_32.pdf). Should give well over 20 Db of clean gain. Look at: http://www.muzique.com/amz/mini.htm or
http://kickme.to/fatboost for schematic

The National Semiconductor circuit is a jfet derivative of an expired patent of a vacuum tube circuit for a "Series balanced Amplifier", US Patent 2,310,342 issued Feb. 1943.

What is you opinion?

Best,

- Peter

 

[jazzpeter65]

Shunt Regulated Push-pull

...Here's the appnote:

 

[dimitri]

Dear Peter, as it seems that nobody else are interested, I offer to continue by

 

[leadbelly]

Dear Peter, as it seems that nobody else are interested, I offer to continue by

I'm very interested, just do not have much to add. So, if you do move off forum, please at least post results!

 

[Devil_H@ck]

I second that, I've been following this with great interest. I'm just not good enough with electronics to be of real help here.

Please, do continue .

 

[dimitri]

Hi, leadbelly & anthony
May be you have some specific question?

 

[AGGEMAM]

Now now there, we could just be lurking here, but still interested in seeing how this evolves ..

Please continue in the open and not via mail.

 

[dimitri]

Mr Jung suggested this link to me, have a nice reading:

http://www.pritchardamps.com/pritchardamps/tech_talk/tech_talk.htm

 

[leadbelly]

Hi, leadbelly & anthony
May be you have some specific question?

No, I just like reading the discussions. I do have a design in mind that I would like to build someday, but that day is a long way off, and that is a super-simple hybrid guitar amp. I am thinking along the lines of a 2 stage preamp made with 6922's (so it can be powered with lower voltages) feeding a chip power amp, so you know where my interests lie.

 

[dimitri]

And another nice link:

http://users.chariot.net.au/~gmarts/guitar.htm

 

[Barre]

New idea

Hi,I've recently discovered this page here and am very glad it exists!!! I've been looking for a FET-preamp design for my guitar for a long time now. I don't know FET's that well yet to desiogn one myself.

Is there a final schematic of the amp now? Or shoukd I continue to follow the first schematic you've posted here?

For me there is not really a tone section needed,since I've got an amp who has great options in this way.
Anyway,for the tonesection in you're pre-amp I'd like to experiment with a Cab Sim I found on the net.

Any comments?
Cheers
Barre

 

[jazzpeter65]

HI Barre!


I'm too much involved in playing music at the moment to try out the FET preamp presented here. Go ahead a try it out. It should work fine. Otherwise you will have Dimitri at this thread - he's a specialist concerning FET's and Tubes...

You could also try out the Skiff Grass preamp as a tube/FET hybrid. It has been built with succes.

Please post your exsperinces here. I'll get back to building mine later this year.

Best,

Peter

 

[dimitri]

Hi Barre,
What style do you play and what pickup/guitar/combo do you have? What would you like to obtain in the long run?

 

[Barre]

My goals

The style I play is metal,sort of metallica-style I'd say.

I own a BC-Rich guitar with standard humbuckers and use a Marshall Valvestate 100R combo (100W)

I set the amp for a "as neutral sound possible" because the music I play contains a lot of clean played parts.

This means I'm not looking for any distortion in a pre-amp what-so-ever. If I need distortion,I'll use my Zoom multieffects unit.

My idea of using the Cab Sim in a guitarpreamp is becuase I thought it sounded good whan I heard it online.
So I thought,why not building it in a guitarpreamp?

So my first idea is:
*guitar to zoom pedal
*zoom pedal to ownmade preamp (with the cab sim in it).
*preamp to the Valvestate where you usually plug in your guitar.


But I also have further ideas that may be better.
My valvestate has an FX loop (send and return) and experimenting with that has learned me that using a external preamp and putting that into the return of my amp, gives much better sounds.
This way, I don't use the Valvestate's preamp, just it's poweramp.
I don't know why,but I like this sound beter.

So another idea would be:
*guitar to zoom
*zoom to ownmade FET preamp (with the cab sim in it).
*ownmade FET-preamp to return of the Marshall Valvestate.

Since I don't know much about FET's yet (we still have to see that in school), I wonder if the posted cabsim can be placed in the FET-preamp posted here...and so replacing the toneregulationcircuit that was in it at first.

So I'd try to build the circuit posted here (if it works,don't know if it's the final schematic here) with the cabsim I posted.
But don't know if it will work.

And if this is possible, is the pre-amp strong enough to feed the return of my Valvestate???

That's about it I guess.
I hope I've explaind it well



Regards and thanks for your reply
Barre

 

[Barre]

Any hints?Sites,...

Hi,

Actually I don't expect you to check what I described up there.
A closer look at the Cab Sim above has shown me that it's just a combination ah filters (HP and LP).
So I think I if I substitute that in the pre-amp above instead of the givven tonecircuit,that will do.

So actually I there's just one question left.
Wil that pre-amp be able to drive the return of my Valvestate (since I don't use the pre-amp of the Valvestate then)?

And my biggest question:
Can you give me some online resources that teach FET's?
I already know transistors a bit, so I'd like to teach myself some FET basics.

Thanks again

Barre

 

[dimitri]

Thank you Barre, for your explanation, I will think and answer, have a hard day today ... I have a schematic of Marshall Valvestate so I get your point ...

 

[Barre]

Thankyou thankyou!!!

Thx Dimitri.

Please do take your time.

I will build this project this summer (when there is no school) and I also prefer to build something after figuering out how things work

I've never found a schematic of my valvestate on the web,but maby I just have to look harder

Thanks again and once more,there 's no rush.
Barre

 

[dimitri]

For the Marshall schematics visit these sites:

http://blueguitar.org/
http://www.marshallschematics.com
http://www1.korksoft.com/~schem/marshallheaven.htm
http://marstran.com

I don’t get the point why you need to add cabinet simulator in the chain, I presume that you have your own cabinet with valvestate.
The cabinet simulator is for direct recording through mixer/computer without microphone/combo or for rehearsal in headphones.

 

[Barre]

Thanks once more Dimitri.

Wel,the cab sim was just an idea.
But you're probably rigt.
I don't use a cabinet, but just the speaker in my combo.

So I guess my question reduces itself to: Can I find a FET-preamp that can drive the poweramp of my valvestate?

The cabsim maby was a silly idea...but until someone gives you some advice,the only thing you can do is experimant.
I'm still looking for "that" sound with which I wanna play.

I'd be glad to try the FEt-preamp posted here,but want to be sure that the schematic is good and not noisy and strong enough to drive the return of the valvestate.

Thanks for the links.