My really simple but useful preamp.

[Zben3129]

Hi All!

Recently I bought some things from the great store here, and when i recieved such great service I decided to join this forum. I couldn't really decide what to do as my first post, so i figured why not post my little preamp. Its only 7 components plus a battery, so very simple. It uses a JFET for the boosting. I have mine in a stompbox form, but im sure with a good vero layout it could be put into a guitar. Hope you enjoy it.




A veroboard layout would be greatly appreciated for those who want to put this inside a guitar or just prefer stripboard over perf.

[alanlan]

The best things in life are simple.  Nice job!

[Zben3129]

thanks!

[petemoore]

  May sound wierd, wrap the circuit in / around a 3/8'' or so dowel rod you've drilled component diameter  holes in to insert/mount components through/on.
  It should be easy to mount, and can be made very small. Made just long enough to wedge in, then a dab of glue...or drill an = size hole to jam it in [not through the top please, maybe mount the dowel to a small square of wood or heavy cardboard layers [like bottom mounting plate], hotmelt glue  or screw that to a control cavity surface].
  *See ROG's perfboard template and print a few blanks for drafting tight layouts.
  Consider the area available for circuit placement and then decide on how to fit the pieces together to fit in, I've gone 'partially boarded' [some connections above board/offboard], even 'boardless' with simple boost circuits, 'hanging garden' style, looks like a cats cradle or spider web, but can be made physically rigid enough...as long as the connections are correctly made, [and no extra's] it will work.
  L shaped board of cardboard, parts HMGlued to bottom/insulation portion, leads through the L's 'side' [where holes have been placed], glue the bottom right on the back of a pot... messy glue look, test outside cavity before installing...
  Build it through holed in one piece of hard cardboard, then put another longer piece over the top as insulation and mount tab piece [after it's verified working, then use two screws to mount it 'end tab' style, strapped flat against the side of the control cavity..
 

[Zben3129]

Wow thanks for the great ideas Pete just what we needed

[Zben3129]

Hmm.....I wonder....In the stompbox form, would it be possible to add a little bit of sweet distortion switchable, maybe one simple knob?

[Meanderthal]

 If ya get good gain, a couple diodes facing both ways, then a pot between output signal to ground, electra style, or a swithc instead of or in addition to the pot...

[Zben3129]

hmm. I dont think there is enough gain in the preamp to engage the diodes. Oh well

[fixr1984]

I did this one quickly. If I missed something let me know.

[stm]

Your circuit looks too close to the schems posted in the links below, even up to the unusual 3M input resistor.  Don't forget to give proper credit to who deserves it.

http://www.till.com/articles/GuitarPreamp/index.html
http://www.till.com/articles/PreampCable/index.html

[Zben3129]

I actually didn't use those schematics at all, and the reason i used 3m resistor is because its what i had laying around from futurlec resistor grab bag, and the veroboard layout looks great.

[Zben3129]

I was thinking of making either a little gem or ruby (runoffgroove.com) and i was wondering.....do you think it would be possible to incorporate this preamp directly before the amp itself in the amp enclosure?

[Dragonfly]

Looks almost exactly like the Tillman Preamp....

only difference is the 22k on input and a mpf102 instead of j201....everything else is the same....

EDIT: I see STM mentioned the same thing....

[stm]

Looks almost exactly like the Tillman Preamp....

only difference is the 22k on input and a mpf102 instead of j201....everything else is the same....

EDIT: I see STM mentioned the same thing....

If you check the second link I posted, you'll see the "cable" version of the preamp does have a 20k resistor in series with the gate.  This convinced me the circuit was derived from Tillman's work.

[stm]

I was thinking of making either a little gem or ruby (runoffgroove.com) and i was wondering.....do you think it would be possible to incorporate this preamp directly before the amp itself in the amp enclosure?

It is perfectly possible.  Take a look at the Grace/Big Daddy article.  You can replace this JFET circuit in there and see what you like best.

[dschwartz]

i dont think tillman deserves mention.. this kind of preamps are too simple to be owned ..there´s not any original, groundbreaking, lateral thinking creative and potent ideas here....
i´ve seen this kind of preamps in basic electronics books, application circuits, many, many boosters.. choosing one or other component value is a matter of taste...

if i have to reference every person that posted this circuit or similar. i´d be writing a big book...

[Dragonfly]

i dont think tillman deserves mention.. this kind of preamps are too simple to be owned ..there´s not any original, groundbreaking, lateral thinking creative and potent ideas here....
i´ve seen this kind of preamps in basic electronics books, application circuits, many, many boosters.. choosing one or other component value is a matter of taste...

if i have to reference every person that posted this circuit or similar. i´d be writing a big book...

Absolutely...but there *is* a difference between "derived from" and "damn near exact".

[DougH]

Sooner or later, different people who build simple single-ended JFET preamps like this for similar purposes are going to come up with similar if not exactly the same ideas. I also don't understand the "Tillman" moniker either. (Saying "Tillman preamp" takes more time than designing this circuit and drawing the schematic on a piece of paper.) Any decent electronics textbook or app note will have a slight variation of this theme as an example circuit. Not worth making an issue over, IMO.

[d95err]

Hi, and welcome to the forum. What an exellent way to start - by contributing a circuit!

If you want to increase the gain (as was discussed earlier in the thread), just add a capacitor across the 2k2 resistor. That will bring the gain up a lot, perhaps even enough to make clipping diodes useful for even more distortion.

The -9V on the schematic should really be 0V. -9V would indicate that your're using a bipolar +-9V supply (total 18V) and that's probably not what you mean... 
Also, please crop the image to include only the schematic. Right now 3/4 of the image is just blank white space.

Keep up the good work! 

[Zben3129]

Thanks foor the feedback guys, and d95err, I'm not at my home computer right now but when i get home I will definitely try out the cap to see if i can increase gain. I will also change the -9v to 0v. I had been having trouble cropping the schematic because my image program exports always with white area. I will hopefully be able to figure it out though