Crawls Backward (When Alarmed)

IconProjects, musings about guitar builds, guitar repairs, vintage tube amplifiers, old radios, travel, home renovation, and other stuff.

Bayou Buffer JFET Signal Buffer


So I ordered up a whole bunch of parts from Mouser and from Small Bear Electronics and now I'm ready to crank out a bunch of stuff!

Funnily enough though, some of the projects I really want to work on keep getting usurped by others.  This one is a case in point.

Since I now find myself with a pedalboard, I am now also beginning to experience some of the issues that I've read about when one has a pedalboard.  Mainly, the dreaded "tone suck." 

Here's the deal:  guitar pickups have a low voltage output.  Also the facts that they have a high impedance and generally run through long cables means that if you run your geetar through a pedalboard, it adds a whole lot more cable length, which means that you lose high-end and tone from the guitar's output. 

I notice a definite difference for the worse when I compare my tone directly into an amp versus going through the pedalboard.  So, I need a solution.

One answer is to use a buffer at the beginning, and possibly the end, of the signal chain.  A buffer is an amplifier that will convert a high-impedance signal to a low-impedance signal.  Low-impedance signals can typically be run through longer cable runs with less signal loss than high-impedance signals. 

I look around the interwebs, and I find some neat schematics.

Before you know it, I've cooked up a version of Jack Orman's Simple JFET Buffer mated to the famous Millenium Bypass created by the famous R.G. Keen.    If you look closely at the image here, you'll see the schematic I scrawled out with the buffer and an added bias circuit for the JFET.  It's becoming scary to me that I am starting to understand transistor circuits!

I originally was going to just build the buffer, but then I decided it might be a good idea to be able to switch it on and off and bypass it.  Not sure why I might want to do that, but it does give me a way to A/B test with the buffer in and out of the circuit.  I'm just going to use a small DPDT switch for bypass, so the Millenium Bypass will do the trick.

I grabbed a small hunk of Radio Shack perfboard I had lying around, and just soldered the whole thing together point-to-point style.  Notice the hemostats on a transistor while I soldered it.

Also note the green arrow.  I cut the board to a smaller size.  Being smarty-pants I figured I'd be nice and tidy.  Ha.

Long story short, I needed the piece I cut off after all.

On the left is the JFET buffer with the bias circuit, and on the right is the Millenium bypass.  I wound up gluing the two boards back together.  Next time, a little more planning might go a long way.

Incidentally, these parts are really small.  I'm kinda getting a charge out of that, since I'm so used to big tube stuff.

So if you were a small bug, or a resistor, or something, and you were on my workbench, this is what you would see.

(My newfangled camera fired off on its own).

So now I have the circuit board(s) all together.  Seems like a good idea to test-wire it all up and see if it actually works.

Sometimes I just 'tack-solder' stuff together.  But this time I said to myself "self, this is a simple circuit.  Choo should just use some test leads!"

You see the results.  Looks like a mess, but it actually worked on the first try!  I must be doing something right.

Then I chust stoof everything into de Hammond 1550B box I have for it. 

The final circuit looks like this.

Man, those parts are small.

In keeping with the Louisiana theme for Crawfish Instruments, I call this the Bayou Buffer.

Yes, that is a bayou in the pixture.

This thing works great at the front of the pedalboard!

I'm plotting a MOSFET version to put at the end of the board to go between that and the amp.  But I have other stuff brewing first.  Circuit boards from San Salvador, El Salvador!


Post a Comment 1 comments:

  • Ulises said...
    November 23, 2012 at 4:25 PM
    Hey man im am very interested on ur buffer with the bypass switch!!! man i would love it if u can make a wireirng diagram for me to build man i would like love u for lifee! :D

Post a Comment