Amp Channel Footswitch

Most amps have the abil­i­ty to use an exter­nal footswitch to change between a clean and dis­tor­tion chan­nel. Of course, some have more sophis­ti­cat­ed options than this, but the chan­nel switch is a pret­ty com­mon fea­ture. My old­er broth­er recent­ly got an awe­some-look­ing, orange Fend­er Duo-Son­ic and a small Fend­er prac­tice amp to play it through. This lit­tle Mus­tang amp has a lot of pre­sets and he can use a footswitch to select between a pair of them. Of course, it being an afford­able prac­tice amp, the footswitch is sold sep­a­rate­ly.

But a footswitch is a pret­ty easy thing to make your­self. In my case, I had the dou­ble pole sin­gle throw (DPST) footswitch tak­en out of my Dun­lop Wah ped­al when I mod­ded it (post to come some­day!) and an old stereo audio jack. That, a bit of wire, and some­thing to put it in is all you need! In fact, the fact that it was a dou­ble pole switch and a stereo jack made them both overkill for this small project! But why not recy­cle the parts for a good cause?

I pur­chased a pow­der-coat­ed 1590LB enclo­sure from Mam­moth Elec­tron­ics. At 2″ by 2″ by 1″ tall, this is about as small an enclo­sure as you can get, but plen­ty big for a small switch and a jack. I got the orange to match his gui­tar (well, as close as I can get with stock pow­der coat col­ors, any­way). I laid out the switch and jack to ensure I could arrange them how I want­ed; though I could have also just had the jack on the “side” of the enclo­sure. The cir­cuit sol­der­ing here is super-sim­ple: just sol­der the “tip” lug of the jack to the cen­ter lug of one of the poles (three of the lugs in a line make a pole). Then sol­der the “sleeve” lug of the jack to either the left or right lug on the same poll of the switch. That’s it! Did you mess up and wire the sleeve to the cen­ter lug on the switch? It’s still fine! All this does is con­nect the tip to the sleeve when the switch is “on” and then breaks the cir­cuit between the two when it’s off.

Now, this par­tic­u­lar build relies on an instru­ment cable to con­nect the footswitch to your amp. But you don’t have to use a shield­ed cable for this as the gui­tar sig­nal itself isn’t pass­ing through that cable; just a rel­a­tive­ly low volt­age (around 4–5v1) is flow­ing through to tell the amp the gain chan­nel should be on. So you could actu­al­ly skip the jack and just use any old wire (speak­er cable, a lamp cord, etc.) and wire that into a 1/4″ audio cable end. I was just using as many spare parts as I could. In fact, I fin­ished the bot­tom by cut­ting up a kitchen jar grip pad and glu­ing it to the bot­tom with spray adhe­sive (it won’t slide on his hard­wood floor!).

Giv­en that the Fend­er sin­gle footswitch costs around $15, this prob­a­bly is not much of a cheap­er alter­na­tive. But it was a fun gift for my broth­er and if you’re inter­est­ed in prac­tic­ing some sol­der­ing, this is a great and prac­ti­cal project to start with!

So, amaz­ing­ly enough, there’s a video in which YouTube chan­nel Mer­win­Mu­sic makes the exact same footswitch as mine — down to the orange col­or! Check it out! He also does a great job of explain­ing how to test out that this sort of switch works with your amp before you go to the trou­ble of build­ing one, which is a good idea as some amps may vary (but all good amps just copy Leo’s orig­i­nal!).

I built this exact same project almost!
  1. The volt­age is low enough that my Black­star head­’s footswitch does­n’t even have a resis­tor on the LED. []

Mini MicroAmp Build

With each new ped­al build, I try to focus on some aspect that makes it a new chal­lenge or some­thing new to learn. My first ped­al build ever (about 18 months ago) was a boost ped­al. I decid­ed I’d build anoth­er boost: this one using the MXR MicroAmp cir­cuit. I used the Gen­er­al Gui­tar Gad­gets MAMP PCB, which in addi­tion to sell­ing the PCB sells entire kits and has excel­lent doc­u­men­ta­tion1. Since it’s a rel­a­tive­ly sim­ple cir­cuit and, there­fore a fair­ly small PCB, I want­ed to try to fit it into a “mini” enclo­sure (i.e., a 1590A for­mat). This means hav­ing to real­ly think ahead about aspects of the build so that every­thing can squeeze into such a rel­a­tive­ly small enclo­sure.

The com­plet­ed enclo­sure, includ­ing the mis-aligned hole for the input jack on the right side

The first thing is that this ped­al for­mat can’t uti­lize a bat­tery for pow­er; the ped­al will be AC pow­ered only. That’s fine as I don’t use bat­ter­ies in any ped­al any­way and only ever added a bat­tery snap to that first ped­al build. Sec­ond­ly, the height of the com­po­nents real­ly mat­ters. The taller com­po­nents (gen­er­al­ly, the capac­i­tors) had to be bent over. For the elec­trolyt­ic capac­i­tors, I had to remove and replace a cou­ple in order to facil­i­tate this (I had planned ahead oth­er­wise — as my sketched notes on the wiring dia­gram shows below, but I am just so in the habit of sol­der­ing the com­plete­ly ver­ti­cal I for­got!). In the end, the tallest com­po­nent off the PCB was the inte­grat­ed cir­cuit (IC), as it was mount­ed in a sock­et. This way I can poten­tial­ly swap out ICs in the future. Speak­ing of ICs, I went with a low-noise TL071 op-amp (in place of the orig­i­nal ped­al’s TLo61 — which con­sumes less cur­rent but, again, I’m not using a bat­tery so I don’t real­ly care about that). The only oth­er mod­i­fi­ca­tion I made to the GGG cir­cuit was that I swapped out a 10MΩ in place of the 22MΩ pull-down resis­tor (R1). Real­ly, any fair­ly large (<1MΩ) resis­tor val­ue will do here and 22MΩ are a lit­tle hard­er to find.

The com­plet­ed wiring. This was a tight fit! Notice all the taller capac­i­tors look like a strong wind came through.

Last­ly, the arrange­ment of the larg­er off-board com­po­nents such as the footswitch, jacks, LED bezel, and pot real­ly came down to mil­lime­ters. I had to use calipers to mea­sure every last item and metic­u­lous sketch it out on a print­out of the enclo­sure. I still man­aged to mess up drilling one of the jack holes (I locat­ed it 1/2 the diam­e­ter off, which s about the worst place to mess it up!). I was able to re-drill the hole thanks to hav­ing a drill press and some clamp­ing blocks. It’s a bit ugly and the jack­’s nut is a bit crooked, but it worked out fine.

Re-drilling a hole for the out­put jack. Drill press & clamps absolute­ly required to fix this sort of bone-head­ed mis­take.

The ped­al works great. I mean, it’s about as sim­ple an effect as you can get. It sim­ply takes the gui­tar sig­nal and makes it a lot loud­er (prob­a­bly around the order of 20–25db). I’m pret­ty pleased with how clean the wiring worked out, as well.

My build cost around $27 for the parts I had to pur­chase. That’s not includ­ing resis­tors, capac­i­tors, diode, and LED (nor hookup wire and sol­der), all of which I already had in my parts bins but would run you around $3 in total. I also had to pay around $9 in ship­ping. The PCB from GGG for was about $3.50 to ship. I bought parts for sev­er­al builds at once in a large order from Mam­moth Elec­tron­ics (my parts sup­pli­er of choice), but small­er orders from there tend to ship for around $5. They have high-qual­i­ty pow­der-coat­ed enclo­sures for real­ly great prices, along with gen­er­al­ly good prices on oth­er parts and kits. So, in total, this build is roughy around $39 in cost (and I still haven’t added any art­work, so con­sid­er what slide decal or oth­er for­mat might cost).

That being said, unless you real­ly want to build your own, I would not rec­om­mend this build to any­one else. You can pur­chase a TC Elec­tron­ic Spark for about $35 used on (plus ship­ping) right now. It has the exact same size as my build, but has their amaz­ing non-latch­ing (relay) footswitch and essen­tial­ly the same amount of clean boost. If you don’t care about size, you can pur­chase a used MXR MicroAmp for around $49 on Reverb (plus ship­ping). Both of those are sol­id choic­es if you real­ly just want a boost ped­al and are less inter­est­ed in prac­tic­ing your sol­der­ing skills or learn­ing how to lay­out a small ped­al form fac­tor. And hon­est­ly, as much as I think this ped­al sounds great so far, those prob­a­bly sound even bet­ter and have less noise at full gain.

But over­all, I’m pleased with this build. On the clean chan­nel, it just gets loud­er with­out adding any­thing else notice­able. Best of all: with the knob set to about 3 o’clock, it makes my Black­star HT-5R head­’s gain chan­nel absolute­ly breathe fire!

  1. I think I could have pret­ty eas­i­ly build this cir­cuit on perf­board, but prob­a­bly not to fit in the this small of an enclo­sure. So for a bit more cost I opt­ed for the PCB, which has a fair­ly small foot­print. []