MIKEMOJO PLANS ...snipped...

This is a simple, easy to build, and foolproof circuit. 
The 741 op amp (operational amplifier - originally 
designed to do mathematical operations in stone age analog 
computers, but the circuit obviously has other uses) is 
ancient, proven, cheap, and stupid simple.  It also has 
poor high frequency response, which is desirable for 
harp mic applications.  For example, it won't oscillate 
at some weird radio frequency if you're a little sloppy with 
your wiring. 

Use two regular 9 volt batteries in series. The mic ground 
and output ground go to the connection between the two 
batteries. Off/on switch can break the connection between 
the two batteries. The op amp symbol is a triangle (yeah, 
I know, mine isn't exactly perfect, but you'll recognize 
it). 

The 741 op amp is in an 8 pin DIP (dual inline 
package) (which means it has 4 pins per side). I recommend 
using a socket and doing your wiring in advance. 

Pin 1 on the 741 has a dot over it. The numbers go in a 
"U" shape. 1 thru 4, and then starting at the end opposite 
pin 1, 5 thru 8 - so pin 8 is directly opposite pin 1. 

Pins 4 and 7 are - and + power respectively. 

The op amp output is shorted to the inverting input. This 
feeds power back into the input eliminating losses and 
making it infinite impedance, which your mic will like a 
lot! Gain is clamped at 1 (unity), so it will neither 
increase nor decrease your mics signal. However, if you 
build it into the mic shell, you may notice more "natural" 
highs (which is good). This is because the cable 
capacitance acts as a "tone control" and bleeds off highs. 
It also skews phase, so you may notice that your mic 
sounds "more precise".


           

          o--------o
          |        |
          o2|\     |
            | >6---o-----o Out
o----------3|/ 741 op amp

(viewed from underneath)

input sleeve o-----------------o output sleeve
   input tip o---o      battery
 input ring      |       clip
       o         |  o----O(+)--o to output jack ring
       |         |  |
       |   1  2  3  4  o-------output jack tip
       |       \       |
       |        \      |
       |   8  7  6  5  |
       |      |  |     |
       |      |  o-----o
       |      |
       o------o


Connect the Positive of battery A to pin 7, and negative of 
battery B to pin 4.

Connect the remaining two leads to the ring and sleeve of your 
input jack, or (better yet) separately to the rings of input 
and output jacks.  Connect the sleeve connections of the two 
jacks together.

I use 1/4" stereo female "guitar" type connectors.  These have 
a tip, ring, and sleeve contact.  For the MikeMojo, these MUST 
be used with standard MONO cables, because the ring and sleeve 
are shorted when you plug into both jacks.  This is our "power" 
switch.

I use a pair of stereo 1/4" jacks.  When either is unplugged, 
the Mojo is turned off.  You could use a single jack, connect 
the two grounds together, one battery lead to ground, and the 
other to the ring of the stereo jack.  If you build it into 
the mic, connect one battery lead to sleeve and the other to 
ground.

Use two 9 volt batteries.  Build the board, and after 
checking all connections, then install the IC into the socket. 
Make sure you don't accidentally bend any of the pins under 
the op amp. Insert it firmly and all the way. If you build 
this into the mic, the output goes to the cord center 
conductor. If you build this into a box, plug the mic into 
INPUT (use a 1/4" jack, or whatever), and your amp input to 
the OUTPUT (ditto 1/4" jack). Make sure you mark the box 
as to which is input and output. Not that it'll hurt 
anything, but it'll save you a little grief at gigs.