I’ve been eagerly awaiting a shipment from Tayda to start this project I’ve been wanting to build from the beginning: the MXR Blue Box! I’ve played through an official re-issue of this pedal and I love the sound… but I’d rather build one. Here’s what I do:
I start with a piece of stripboard (also called veroboard or prototype board). It’s made out of something like thin plywood with a grid of holes on the front and strips of thin copper on the back… so, any components mounted in the grid become connected with everything on that row. Convenient and a nice half-way point from working with perfboard (which has no strips) for complete DIY building. I’m building this up based on Harald Sabro’s excellent layout
Like I said, the stripboard is made up of rows. This is a bigger circuit though so we make some cuts in the strips to disconnect some of the components from eachother. You can use a drill for this but I prefer my trusty Leatherman… PS at this point I have already made a mistake and put the very first cut
I made in this board in the wrong place… it’s good to be careful and precise but I just lack that ability sometimes. I bridge the incorrect cuts and the results are not pretty, but work.
Here’s all the cuts in place. You can see a few areas with bridges I had to make (mostly on the right side of the board in this photo) and how some of the copper is burned already… beginner’s solder technique at work here. This one’s a beast with 29 cuts total.
Now I’m populating the board. Starting with the jumpers! These connect the rows we just cut apart back together in the order they should go… I re-use wires cut from the ends of components from old builds for these, except a few longer ones which I use lengths of insulated wire for. Then I add the rest of the components, from shortest to tallest. I love this part! I could do this all the time and I wouldn’t mind if nothing I built ever worked (I don’t mind!), placing components is so satisfying.
First the diodes (the little orange and black things). These things are great
. They’re responsible for the signal clipping that creates my beloved distortion. They’re about 2mm long but are utterly important! The original bill of materials called for 1N914 but I only had tons of 1N4148s, a more standardized modern replacement/equivalent. It would be interesting to get some of the original value diodes and compare the sound…something to try in the future! The resistors… I try to use just one material per build but a few of the values I did not have in carbon film (tan ones) so I used a few metal film ones (blues).
Now the sockets… in past builds I’ve used way more to socket the input and output caps, mostly to up the values for a bassier sound (for DOOM) but I opted only to socket the ICs and transistors this time. This is just a really good idea because these parts can be finicky, especially in germanium builds, and its easy to burn them up applying direct heat to them. PS that’s my 25W Weller which has some sweet built-in LEDs to help me see what I’m doing. Luckily the tip isn’t in the photo; it’s degraded almost to the point of unusability.
Here’s the caps. I like to use mostly all the same material if I can in a build, these are all Mylar film “Greenies.” The layout did call for one 330pF cap which I used a ceramic disc for, its barely visible in this picture behind the IC socket on the left. I love capacitors too… as I mentioned it can be very easy to hear the difference in the sound of a whole circuit by swapping one cap in the signal path. Some commercial pedals are marketed as entirely different “versions” (i.e. “for bass” or “for guitar” usually) which have just a couple changed caps between them. A single cap is responsible for the action of a tone control on a guitar, too. Rad…!
This somewhat “artsy” photo shows the ICs in place, on the left a JRC4558D from Small Bear, I wasn’t aware previously that these had a reputation as “mojo” pieces due to their use in the legendary TubeScreamer… just a dual op-amp in an 8-pin case! On the right is the special chip I bought (several of) just for this project, a Texas Instruments CD4013BE which is a “Dual CMOS Flip-Flop”… of course I don’t really know the technical details of what that means… but its responsible for the gnarly low-octave the Blue Box puts out. Also visible are the transistors, all three 2N3904s, simple and very common NPN low-power amplifier. Oh yeah and the electrolytic caps are in now too… these are mostly for power. Aluminum polarized cans and the tallest components on the board. And that’s all the on-board components btw. Phew!
Lastly the wiring. The two 50K logarithmic pots control Blend and Output and they wire up pretty simply. I’m using the last of my 22-gauge stranded here from RadioShack. There are a number of ways to wire the offboard components (audio and power jacks) but I like |\/|ark’s method
. Wiring can be kind of the least fun part, but the Klein wire strippers I use make it pretty easy and, quite enjoyable sometimes!
Now to wrap things up my Blue Box circuit does not work yet. You can see in the last photo I left the (green) output wire to the output jack unconnected. This is because I figured I’d need to troubleshoot the circuit, which is the step I’m on now. About 2/3 of the board is working properly and receiving the audio so it’s just a little bit more debugging that’s left! That’ll be for next time, and I’ll take some better pictures of my next Scuzzbox build with a better camera… turns out the one on the Kindle Fire isn’t so high-res… woo!!