Easy DIY Pre-Amp: Makes Piezo-Equipped Cigar Box Guitars Sound Better

Reduced feedback.  Deeper bass response.  And no more "quack!"

We were complaining about all the problems with piezo pickups when the idea for this standalone pre-amp came to me.  It's deceptively simple... a $17 acoustic guitar pre-amp with a hacked input becomes a great EQ and signal boost.  And it's all housed in a cigar box!   

First of all, here's how it sounds...

I built this prototype in less than one hour.  Here's how to do it:

PARTS NEEDED:

  1. C. B. Gitty Pre-Amp Unit Model EQ-7545R ($16.49)*
  2. 1/4" guitar jack ($6.49/3 pack)
  3. Empty cigar box that is deep enough to house the pre-amp.  These boxes from Gitty are a good example. 
  4. 9 volt battery

(*Note: a piezo rod pickup is included with the pre-amp.  We'll need this!)

TOOLS NEEDED

  1. Wire stripper/cutter
  2. Soldering Iron and solder
  3. Coping saw, scroll saw or Dremel rotary tool.
  4. Small #1 Phillips head screwdriver

Here's a quick overview of the process.  We'll get into detail with photos after the video:

STEP 1: Cut a 3.5" x 1.5" hole in the box to fit the pre-amp.   You can use a coping saw, carpenters knife or a Dremel rotary tool with a cutting disk. 

STEP 2:  Drill two 3/8" holes in the box, one for each guitar jack needed.

STEP 3:  Take the rod piezo out of the pre-amp packaging.  Using wire cutters, cut off the rod piezo pickup from its wire.  Cut closest to the pickup, leaving the longest length of wire possible.

STEP 4:  Pull back the ground wire sheath to expose the lead wire.  Strip off 1/4" of the lead wire's insulation.

STEP 5: Solder the ground sleeve wires to the ground prong (the inner, circular portion of the jack).  Solder the lead wire to the other prong (the lead prong) of the jack. This is now our hacked pickup wire and will become the input jack.

STEP 6: Insert the 1/8" plug of the hacked pickup wire into the receptacle of the pre-amp unit.

STEP 7: Install both guitar jacks to the cigar box.  I would recommend positioning the hacked wire (Input) on the right side of the layout and the the black plastic jack (Output) on the left side.  Also insert the 9 volt battery at this time.

STEP 8:  Mark your input and output jacks accordingly.  I used a woodburning pen.  You could use paint or any other method.  (Remember, this pre-amp in the photos is a prototype. My next one will have a cooler layout, better graphics, a carrying handle and feet!)

OPTIONAL- ADD A HIDDEN GUITAR PICK CADDY:  If there's extra room in the box, you can glue an Altoids tin to the bottom.  I simply used a hot glue gun to attach the bottom of the tin to the inside bottom of the box.

ADDITIONAL NOTES:

  • Unplug the guitar cables when not in use or it will drain your 9 volt battery.
  • Dialing-in the right tones is an art.  Each instrument is different.  The pre-amp is there to sculpt the tones ... and to also give signal boost to low-output piezos.
  • If the guitar sounds too distorted, try dialing back the volume on the pre-amp and increasing the volume on the amp/PA system.
  • If you sell cigar box guitars with piezo pickups, these pre-amps could be a great way to make additional income.  Get fancy with them and give them a product name.

Good luck!

-Shane Speal, 2016 

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Good idea Shane.

Great tutorial Shane.  I made one of these over a year ago and they work just dandy.  The equalizer is a plus and like you say, the low cost makes this an attractive option.  One thing I like about it is it's a "simple" unit... none of the garbage we see on other preamps to muddy up and confuse the situation.  Simple volume and equalizer.  That's my kind of preamp.

It would be a good idea to have one in a pedal chain/pedal board too.

Very helpful.  Thanks for posting this.  I have been kicking around the idea of building a stand alone preamp, and this just cleared up any questions I had.  

Is it a standard 1/8 (3.5mm) mono audio TS on the piezo?  I'd almost rather get the solder yourself male connector and make up the 1/4 F to 1/8 M cable and use the piezo on the git...

It's always better to install the pre-amp directly in the guitar...however, many of us have CBGs with plain pickups and no pre-amp.  This stand-alone unit allows us to properly EQ and boost those older guitars.

Yup.   Especially since it allows us to use one preamp on several gits rather than having to invest in separate preamps (and batteries) for each git.    If we have just one or two CBGs and that's all we ever play, it's probably good to just go ahead and install the preamps in the gits as JL suggests (and Shane verifies).   But for those of us (like Shane and JL) who use CBGs instead of wallpaper... a central preamp box can be pretty handy.

As an additional design note:   one can install an on/off switch in these to eliminate having to pull the guitar chord, but it takes a bit of wire searching and soldering to do so.   I just pull the chord.

EDIT:  You know you've been playing CBG too long when you spell "cord" as "chord".

What I meant was, instead of cutting the piezo wire, will the pre-amp accept a 1/8" (3.5mm)  male end plug? 

I have a few ideas rattling around the empty corners of my noggin about saving the piezo intact for something else.

Sorry JL I just saw this post. 

No, this particular device won't accept a standard 1/8" plug; the plug is considerably smaller.  You can however save the piezo intact for another project; just cut the lead wire in half and splice in another wire.

Neato and uber sound too. Looks like an awesome bit of kit to confound the muggles even more and enrage purists of the  sacred, store-bought axe. I must give this a go. Thanks Shane, and all the best with your online concert too.

Brilliant!
Great Stuff!!!

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