MPC Builder

This is a new page that I am trying out to share with all you Electra MPC enthusiasts.  I hope the resources shared on this page will offer some joy and fun as we try new thing with a classic instrument.

I have been so frustrated lately trying to find Modules for my Outlaw.  Most people want to keep their modules, and we who are missing modules cannot get our fix.  So I decided to try building a module just to see if it could be done.

The challenge, of course, is to find or create a circuit that can use the exiting wiring and 150k pot built into the guitar.  This was a fun challenge for me because problem solving has always been my greatest love (after my wife, of course).

I ended up going for a modified Box of Hall reverb unit.  Since I don’t currently have an amp with reverb, this was a good choice for me.  The simple circuitry and ability to fit it into a tight space makes it a perfect choice for a first try.

I used Eagle, an AutoCad circuit poard freeware to design what would become the board.  I tried double sided and single sided boards.  I ended up going withthe single sided option because it is much easier than trying to “rivet” top traces to bottom.

So, here is the circuit I came up with.

single sided reverb schematic

The potentiometer in the schematic is actually the one in the guitar.  The outputs from the BTDR2-H originally had a “depth” pot, but I removed it, along with the capacitor connecting it to ground.  I also had to add a resistor at the output because the output was way too hot (with no level pot to control it).

Next I used the Eagle software to design the board itself.  there is a heavy learning curve here, but it’s well worth it if you plan on doing any of these yourself.

Here is the final board design I came up with.  It’s similar to the Box of Hall, but positioning changes and additions were needed to accommodate the profile of the box.

reverb pcb bottom

The box build was tricky.  The board is 54mmx64mm with a 10mm “tongue” for the connectors–easy enough.  The hard part was finding material that was tough enough to be sturdy, but thin enough to not overcrowd the cavity where the modules plug in.  Oddly enough, I found the solution at Lowes.  Their vinyl siding samples are the perfect material and size to build this box–and they are free samples!  I’ll leave it to you to figure out the details, but here is the basic box I came up with:

box beginning

Etching the pcb was probably the most fun I’ve had with electronics since high school.  Again, I’ll leave it to you to research etching techniques and board suppliers.  One note to be aware of, however:  when buying a board blank, it must be 1/16 inch thick.  There are thinner boards, but you will lose sufficient pressure on the connectors–trust me on this!

Here is the tinned pcb after etching.  The resistor on the bottom was an attempt at modification which I removed later.

pcb bottom

And the top after soldering the components:

pcb top

One note about assembly:  when I soldered the op amp IC, I used a socket, which made the reverb brick higher than I intended.  It still barely fit, but it was close.  In future, I would probably solder the IC directly onto the pcb to lower the profile.  Also, the above pdf of the pcb traces reduces the number of jmper wires to 4; but due to the reversing of the reverb brick from the Box of Hall (to shorten the overall profile), routing traces took up needed space for adding the MPC connectors.

After testing the board in the guitar, I assembled the board in the box.

board in box

Gluing is not my strength, but finding something tht bonds pvc (which is what the box is made of) was tricky.  But there it is.

Finally, the ox complete, I stuck it into my Outlaw, and did a final test.

verb in guitar

It sounds good–with one exception.  As you turn the pot, the reverb increases normally, but there is a slight volume drop in the middle (“0” and “10” are louder than “4-7”).  I’m still pondering this.  Overall, however, it’s a great little addition to the 12 modules there are available (available in theory, anyway).