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tiny boost for piezo


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  • tiny boost for piezo

    Anyone know of a booster I could put together that would fit in half of an MXR box?  I have an MXR micro amp case that I repurposed for and undo footswitch for my JamMan looper.  I really need a boost/preamp pedal for my piezo/fake acoustic, but my pedal board is full.  If there was some simple boost that I could put together that I could stick in that same enclosure, it would be ideal for me.  I could relocate the existing switch if I had to do an 75/25 or 80/20 share between them.  I was thinking about some really small thing, like a booster intended to be onboard.  I was looking at the AMZ mosfet as well, but it doesn't look to me like I could fit it in there if I buy his circuit board.  I was hoping there was something out there that would fit on a 1x1" breadboard that had a footswitch.

    Too tall an order?


  • #2

    Listen, if you don't need tremendous gain, what you can do is built a FET preamp that is on the guitar side, right on the instrument.

    And the best part is, you do not have to modify your guitar in any way.

    The preamp can be in the guitar cable plug, on the instrument side. 

    Your half a MXR box will still be used: it will house the circuit which provides phantom power to the preamp, by generating a DC voltage over the instrument cable.

    Here is the project, by Don Tillman:


    And, by the way, instead of using a JFET, you can use a depletion mode MOSFET. (This is a special type: the most widely used MOSFETS are  "enhancement mode").  Depletion mode MOSFETS are biased identically to JFETS. They are normally on, and the gate voltage is brought lower than the source to cut them off.  The current versus VGS curves follow the same math.  The possibility of using a depletion mode MOSFET increases the choice that you have in parts selection. And, also, because it's a MOSFET, it has an insulated gate, so its input impedance is higher than that of the JFET, and it doesn't have a problem with the gate voltage rising a few volts above the drain voltage, whereas a JFET's junction will forward bias in that situation.





    Music DIY mailing list: http://www.kylheku.com/diy
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    • thewthrman
      thewthrman commented
      Editing a comment

      I like that idea alot, but I was really fixed on having a footswitch.  For live playing with a looper, I have a piezo-equipped electric running into a Zoom A2.1u (with volume pedal).  But I usually forget and have the pedal floored when I record the loop.  Then if I try to solo over it, I am drowned out.  I was thinking that a spring mounted under the pedal so that at rest it is at 85% or so, and then I could hold it down for the full 100%.  But I just never came up with anything mechanical that could do that - yet.  I started thinking about a boost/preamp pedal.  I could fit a Spark or EP on my board probably. And it would likely look cool.  But, given that a stratoblaster kit with switch is like $25, maybe that would be cool, too.

      I am gigging tonight.  When I get home I am going to take another look to see if there is something I can rig up for the volume pedal.  I figure one of those springs like in a clothespin would work, wouldn't it?  Maybe it needs ot be bigger.

      This might turn out to be more of a hack than a DIY booster thing.  I'll keep you posted.  Now I am off to google most of the stuff in your post.  If I did build a booster, it would be a first time project for a guy who has smoked many, many components over the years due to poor soldering technique.