GM Arts Overdrive Pedal Build

Here I am going to document one of my most successful electronics projects of all time. If you play the guitar and you can build electronics then this is a perfect fit for you! I found the schematic for this project on the Internet here:

http://www.gmarts.org/index.php?go=217

Scroll down to the bottom of the page.

You can get the schematic the same place I did, from the bottom of the page. You know, "save image as" in your browser. Or in Linux:

wget http://www.gmarts.org/pix/schem/a_amp-odis.gif

Should do a good job of snagging the schematic for you. I don't do Windows so if you do you're on your own there.

I'm also going to attach my Eagle .sch file here as well. Eagle in case you don't know is a schematic capture and board layout program made by a company called Cadsoft. I use the free version because I am just a hobbyist and I really don't want to make a board any bigger than they allow you to in the free version anyways. So the good news is all the files I make you should be able to open up and work with in the free version!

If you don't have a copy already get one, playing around with Cadsoft's Eagle is more fun than playing video games. At least it is if you're an electronics nut like me. The bad news is lots of folks seem to have problems opening sch and brd Eagle files from different versions and my version is pretty old 5.10.0 is what I have. Now if you have that problem I guess you're just going to have to look at my screen captures and try to make your own that works with the version of Eagle that you have. Hey it's great practice! If you do that be sure to attach yours to a comment in my Instructable. Thanks for sharing.

One other thing to note about my schematic and board files is I use header pins instead of potentiometers and jacks because I'm going to be connecting my parts with jumper wires to my board. I laid my schematic out a lot like the original graphic so just try to follow along OK?

This circuit looks deceptively simple in the schematic. I built this thing so trust me its pretty complicated physically. But if you etch a board for it then it builds pretty easily. I put mine together in a couple of hours. I guess what I'm trying to say here is yeah you could build this circuit on perfboard or veloboard or stripboard maybe but if you do it is going to be pretty tough and probably come out kind of rough.

Hey it is up to you, I suggest you etch a board for it though. You don't want your mad effect dying on you when you're on stage doing a gig do you? On this page I am going to put up a screen shot, then my Eagle brd file of artwork for etching this circuit. The layout I did for this board isn't optimal but it is good enough, it could probably use some more work honestly. Who knows maybe my sloppy layout is what makes mine rock so hard!

This is a parts list I made for when I built mine. Let me know if I left anything out.

R1  22k
R2  22k
R3  22k
R4  1k
R5  2k2
R6  10k
R7  10k
R8  560k
R9  39k
R10 4k7
R11 100k
R12 10k
R13 39k
R14 6k8
R15 390
R16 560k

C1  220uf
C2  220uf
C3  .15uf
C4  100pf
C5  2nf7
C6  10nf
C7  .47uf
C8  .1uf
C9  .1uf
C10 6nf8
C11 3nf3
C12 .47uf
C13 .1uf
C14 .01uf
C15 .01uf

D1 1N4004
D2 1N4004
D3 1N4004
D4 1N4148
D5 1N4148
D6 1N4148
D7 1N4148
D8 1N4148
D9 1N4148

Z1 5.1V
LED1 5MM
T1 BC549
IC1 LM4558

SL1 POT1 1M LOG
SL2 SW1 SPDT
SL3 POT2 50K LIN
SL4 POT3 50K LOG
SL5 SW2 DPDT PB
SL6 SW3 SPDT
SL7 SW2 DPDT PB

Whoa! I sure hope you have as well stocked a junk box as I do or you're going to make your local Radio Shack dealer rich! I didn't buy a thing for mine. It is pure trash. When you see mine it'll look it too.

One other thing I should mention about the parts I used for mine as opposed to what was called for on the original schematic is the op amp I used. In the original schematic they called for using a TL072 dual op amp. I used a vintage JRC4558 in mine. Those are much sought after devices for use in guitar over drive units for whatever reason. I don't see a reason to use a particularly clean amplifier in a device I am looking to get distortion out of anyways. I'd imagine just about any dual op amp would work with this circuit so the choice for what you use is up to you.

Now we need to do is decide on a method of pattern transfer we'll use to get the board art onto the copper clad printed circuit board stock material that we'll be using. I've used a product called Press-n-Peel but I have to say I have not been completely satisfied with it. I have heard high clay content paper works better, even glossy magazine pages without much printing on them I've heard work too. The best method is photo-resist but that is complicated sounding to me and I have never done it myself.

I haven't tried any of those methods out myself other than the P-n-P Blue. You're going to have to decide for yourself just how you are going to transfer the board art onto your copper clad circuit board material. Share your stories in the comments what methods you use and why and how you like them. I know I'd appreciate hearing about it.

You should be able to tell in the picture that before I transferred my etching resist onto my clad board I cleaned the copper and polished it up all bright and shiny. This is important so the acid can get right down to the copper and work on it.

Check your resist however you do it and insure that there are no breaks or cracks or hairlines that may cause you problems etched away. Repair them now with a permanent marker if you find any. You can see in the second attached image I liberally touched mine up before I etched it.

Ferric Chloride acid that is. I've had hit and miss using this as well. I have found out a couple of ways that do make FeCl3 work a lot better though. I'd like to share those with everyone now.

The first thing I do is I heat my acid bath up. Oh there is nothing a PCB likes better than taking a dip in a nice warm acid bath ... but I digress. Seriously if I heat my acid bath up to just about fuming the acid is much more aggressive than at cooler temperatures. I've had etches completely fail on me using too cold baths. I've had etches come out great in less than two minutes using warmed up baths too. Great is what we want so if you're using Ferric Chloride make sure you are using it hot.

In my attached image you should be able to see that I use a water bath over a heating element to heat my acid bath up. In cooking this is called a bain-marie. Though I don't think I want to eat this dish! Anyhow, I'm sure there are other ways of getting your acid warmed up. This way works great for me though. Share your method.

Something else I want to point out now is how I agitate my etch. I've done the whole rock the pan thing to death and frankly it isn't much fun. I can't even say it works so well having done it as much as I have. But I have found something that while maybe not as much fun as a barrel of monkeys isn't so drab to do as rocking the pan and works great!

I researched how printed circuit board are etched commercially and one thing that came up time and time again was air entrancing. Sounds scientific. All it means is mixing air with whatever it is you happen to be working with. Duh, I can do that! I have a couple of air compressors so initially I used one of my big ones and an air regulator. When I moved I moved my air compressor but was still at my first house and wanted to make a PCB, what to do?

Well I had one of them old plug it into your cigarette lighter tire inflation air compressors kicking around still. I'm telling you now even though I have a big air compressor and a regulator blah blah blah for doing this air entrancing acid bath the thing I'd reach for today is one of those horrible little tire compressors. The pulsating air stream they put out is perfect! The worse a one you can lay your hands on the better for this. Just so long as it puts out some air.

In my second image on this page I will show the air nozzle I cobbled together out of an old tire valve stem and some rubber hose with an old aerosol spray cap as the nozzle. A word to the wise though while you are setting up your air entrancing mechanism test it out in clean water. Ferric Chloride isn't the kind of stuff you really want to blow all over the place. What you're looking for here is bubbles in the liquid. Sort of like it is boiling almost. As much agitation as you can reasonably come up with while not getting FeCl3 all over the place, lets not get too carried away here.

Any questions ask in the comments and I'll try to be clearer about any of this. I know I didn't explain every gory little detail going on here. I hope I gave everyone some ways to get going though.

OK you've gotten your board to etch hopefully now it is time to pull it out of the acid bath, kill the etching process, and clean the resist off so you can solder to your new printed circuit board.

I keep a container of water next to my etch tank while I am etching so I can dunk the board in there when I am done, or maybe just to swish it around so I can see what is going on during the process. once I am satisfied with my etch I rinse it one last time and move on.

Moving on in this case entails scrubbing the resist off the remaining copper cladding. I use acetone and some steel wool to do this. If using steel wool make sure you do not leave any behind as it could cause shorts in your circuit later on.

Pretty straightforward step here. Drill holes into the PCB where you need them for parts. I find having a printout of the board with the parts layer displayed helps me with this step.

In the commercial PCB assembly trade this step is called parts stuffing. Because well you stuff parts into the board I guess. A few points about proper board assembly are in order for me to make here. Stuff maybe even a seasoned hobbyist doesn't know. I've done this professionally so I've been told in no uncertain terms that there is a right and accepted way of doing these things. I shall recount them now.

Decide which is the top edge of your board, then orient all components so they either read left to right, or top to bottom, unless the component has to go in the other way for reasons of design and polarity. This means the multiplier band of a resistor is either to the right, or the bottom when the top of the board is in the top position.

When you form your parts before stuffing them into the board if there are any marks on them ensure that those marks are visible on their tops.

In the attached image you can see that I've printed out a top mask of the circuit board then stuffed the parts into it, on foam, where they each belong. This is just something I am doing to ease the construction burden on myself. Commercially it isn't done this way, but each part is put into multiple boards in turn. I'm only making myself one board today so this is how I am doing it.

I tape my parts to the board before I flip it over to solder. Your best plan is to solder all of your lowest lying parts first, then add the taller parts later. It just works out better doing it this way.

Solder your parts to the PCB. I don't know what else to say here. Although there is an awful lot that can be said on the topic of soldering. I'll just say do a good job and leave it at that.

Assemble everything, hook it all up, you know the drill. I suppose I should address the issue of enclosing this project somewhat here. I made a custom metal box that honestly if I had it to do all over again I'd do something different. All I can say is it seemed like a good idea at the time. I'm glad it is done now, but it could have gone together more easily. I like how it is now but let me just say I'm glad I'm not messing around with it anymore.

Maybe you'll take the time or have the foresight to come up with a better enclosure solution than I did having so much of the project laid out before you begin? Anyhow I'm not going to delve into all the sordid little details of my case as they'd do no one any good to hear.

You can do better than I did I know you can! Mine does look sort of heavy metal cool though doesn't it? Maybe put some burns on yours too while you're in the process of making it?

This is a major project and who knows at the end of one of these if it is really the end or just the beginning of the debugging phase. Mine worked right off the bat but I wasn't about to plug my vintage Gibson SG Special into it initially I can tell you that! I tested mine out on my bench with a signal generator and everything looked OK to me. Maybe you have a cheap guitar lying around you can use? Maybe you're richer or braver than I am?

When you're building electronics circuits of any complexity anything can happen and I'd just like to take this time to point that out. We all make mistakes, some of us just take precautions ahead of time to minimize the damages those mistakes can cause. Some sleep under the stars after they've burned their houses down around their ears too.

Who is to say which path is correct? Well, you are! Choose wisely.

The finished project in my effects chain. I may not be the world's worst guitarist but I bet I rank in the bottom 10 or so. That having been said you can sort of hear what this effect sounds like here: (warning: I'm pretty bad playing guitar now don't say I didn't warn you)

http://www.youtube.com/watch?v=VINRCVg5Dls

Or skip that and build one yourself. I think the only reason I play the guitar is to mess with electronics. Before anyone comments on just how bad I am save the electrons, I know how bad I am! But this overdrive pedal is bad too. Bad to the bone that is. I've heard what people who can play sound like through it. I want to hear what you sound like playing through yours so build one and Rock On!

If I have any left I'll patch the first person that puts up a picture of theirs and a link to an audio clip. You'll have earned it.