This will be a power source and chassis for a valve-based guitar effect pedal. I was figuring this out as I went so the progression I will be showing wasn't necessarily the order I took-- what follows is an idealized route, re-arranged and un-besotted with the false trails I had followed.
This particular pedal will become a tremolo effect based on a 1960s Fender Vibro Champ, although once you have a power source, two tubes, in- and out-phone jacks, and some controls, you can build 95% of the fuzz/tone/tremolo valve circuits out there. Many people struggle with the metalwork for stomp boxes and I hope that this instructable will give people a leg up on their projects. More than anything I want to give you, the reader, confidence. Realize that the tools I used aren't expensive or esoteric, and once you have them several worlds open up. I was working on a 16 x 26-inch slab of wood sitting on a dining table with occasional field trips to the balcony floor whenever I felt like getting loud.
Aesthetically I'm going for a kind of steam-punk, but depending on the colors and materials of the miscellaneous details a broad range of genres can be achieved.
This project involves high voltages that can kill you.
If you don't feel comfortable with line voltage (which, by way of the power grid, a true feat of engineering [thankyouverymuch, forebears], will produce as much amperage as it takes to kill you, and will do it without noticing your thrashing corpse) and high direct current voltage you should step back, do some reading, get confidence in your soldering technique, and then embark on the happy journey of obsolete (yet occasionally superior) technology.
Here are a few good starting points:
...then pick your way around the rest of Tube CAD Journal
Aiken Amplification has a great Tech Infosection
Basic Tube Formulas
Some good articles about DIY sound, also a host of a DIY forum and seller of kits
...some other forums:
Hoffman Amplifiers also sells parts and has a great library.
Start at this page DIY Basics and the rest of this forum is great as well.
Between the articles and the forums you'll find most everything you'd need to know, certainly enough to start by and probably enough to keep you busy for a good long time. Read around before you start posting. Most forums are populated by VERY gracious people who want to help anyone who shares their passion for DIY audio, but let's not take advantage of them. Do your reading.
Tools you will need:
Drill and Various Bits
Soldering Iron plus Affiliated Affects
Step 1: The Chassis
We begin at the perimeter of the pedal. This material can be found at most hardware stores, scrap yards and street corners. I do not promote the theft of DOT property, just sayin' as visual reference. You will need two feet of the the inch-and-a-half square weldable steel tubing, depending on how closely you stick to these plans.
Take your angle grinder and cut the square tube down the center the entire length. Use hearing and eye protection, for !@$% sake. You will want the use of all of your faculties to behold the consummation of this project.
The holes on the tubing are one inch on center and I want the corners to fall on the solid portions. I marked fold lines (starting at one edge) at three inches, from that point eight inches, from that point six inches, from that point eight inches, and from that point I marked a cut at three inches.
I then drew 45-degree lines radiating from the fold lines. These 45s are cut-lines for the corners. I will be folding these by hand and will not be welding them in place, so I made the 45s meet up a little behind the side that will be folded. Pictured below is an exaggerated example of this; to its left is an example of the lines I actually used. This will give you a gap between the cut edges when you fold the metal together, as you will have to over-bend the corner slightly to get it to stay at a right angle.
Once things are cut you can fold it up, starting from one end to the other. The ends didn't quite match up for me so I used three clamps the hold it flat and to make the ends meet. Now I'll button it up using a little plate I ganked from a crappy flat-pack chest of drawers I found in the trash (other parts of it are now book shelves and a spice rack. The gift that keeps on giving.). You can use any piece of metal, but this one already had beveled edges and bolt holes. Saved me forty seconds, at least.
I wanted a unique and vaguely silly way to carry the pedal--plus a way to make it easy to pick a new strap. So I decided to give the pedal guitar strap buttons so you can use any guitar strap to carry the pedal like a satchel. I know Chewie would be all over this. For this vision of perfection I only needed to drill and tap a hole at the first space on both sides to take a 1/4-inch brass bolt. I cut the bolts so that they would be only just long enough to penetrate the square tubing and a lock nut, with a small gap for the strap on the outside.
The holes on the side of the tubing are the perfect size for phone jacks and there is room for two on one side of the tubular plate; on the other side, the holes can be used for the power supply. You can use a strain relief on one hole to feed in the power cord and a fuse holder at the other (like the P-H1200 and S-H205, respectively, at Antique Electronic Supply).
I, however, prefer detachable power cords--if it's damaged, you can easily replace it. Plus, as you use the pedal in different settings, it lets you find that perfect length, so there is one less thing to be bothered with. This means Mr. IEC Socket and his dinner guest Mr. Square Hole--which is where most people politely excuse themselves, suddenly remembering the grand opening of a Denny's down the street, where the remainder of the party-goers will re-form and spend a happy evening in Mr. Square Hole's absence, made all the more pleasant by the near miss.
I do enjoy a bit of misery, and metalwork for an IEC is at that level where one can proudly look at one's self in the the mirror without having to live through, for example, a governmental destabilization. Four drill holes and two broken Dremel blades later I can hold my head high.
Step 2: The Power Supply
I will not be feeding this pedal 18VDC. I say pompously: that is not how valves work. They will accept that voltage with a smile and a barely perceptible cringe; but the fact is if you want to be feeding the air with valve-induced vibrations you will need to work with high voltage, as the low voltage does not allow the gear to work at its full potential.
This particular power supply will give you a regulated 12VDC for the heaters and unregulated 290VDC for the B+ supply. A larger resistor than the 1k 1W or a choke will get you a lower voltage--I felt that 290VDC is a good starting point.
The 12VDC regulator needs at least 13VDC at its input and you'll want to aim a little higher to guard against fluctuating wall supply. Conversely you do not want to introduce too high of a voltage as the regulator will convert the excess voltage largely into heat.
Remember that transformers transform voltage. They do not have a set input and output, only a set ratio of input to output. When a transformer says it has a 120VAC primary and a 10VAC secondary it's really saying that its two windings maintain a 12:1 ratio with each other. Thus 120VAC on the primary makes 10VAC on the secondary---and---10VAC on the secondary makes 120VAC on the primary--AND---3VAC on the secondary will make 36VAC on the primary.
The other conversion you need to start off understanding refers to power handling. If the same transformer as above has a 2 Amp rating then you can multiply 2 Amp with 10VAC to get 20VA. Now whatever voltage you get from a transformer you can divide the VA rating by the final voltage, regardless of which winding provides the final voltage. In the above examples, 120VAC would handle 0.16 amps or 160mA and 36VAC would handle 1.8 Amps.
The first transformer in line produces about 16.5VDC when rectified, which will keep the regulator happy. The first transformer also sends 12.6VAC to the next transformer, which is flipped so that the 12.6VAC goes into the secondary winding and becomes 216VAC at the primary winding, which rectified becomes about 300VDC. This is dropped to about 290VDC by the 1k resistor.
Here is the part list for this particular power supply:
Item, Mouser Part Number
Power Transformer (PT1), 12.6VCT, 546-161GA12
Power Transformer (PT2), 7VCT, 838-SB3512-2014 (older PT2)
Power Transformer (PT2), 120CT, 546-186B120 (recommended PT2)
x2 400V 8A Bridge Rectifier, 621-GBU804
3300uF 35v Electrolytic Capacitor, 647-UPM1V332MHD1AA
12V 1.5A Voltage Regulator, 595-UA7812CKTTR
1N4001 Diode, 863-1N4004G
220uF 35V Electrolytic Capacitor, 140-XAL35V220-RC
450V 22uF Electrolytic Capacitor, 647-UVZ2W220MHD
x2 450V 47uF Axial Electrolytic Capacitor, 140-XAL450V47-RC
1k-Ohm 1W Resistor, 594-5073NW1K000J
Illuminated SPST Switch, from Radio Shack
The cost for these parts should be around $30 including shipping. Please note that some of the parts pictured are things that I had laying around, but the parts I list above will match them functionally. The two axial 22uF 450v capacitors will attach directly to the tube sockets. These are still part of the power supply and will be used by almost any effect.
Here's a larger image of the schematic and PCB
One can build this on a breadboard, though I might suggest gluing two pieces front to front, then soldering all the connections you can reach on both sides, giving a better mechanical connection. The layout I'm including is positioned on a grid that matches a typical breadboard.
I used a nice, thick copper-clad board. For this, I drew the layout on graph paper, glued it to the PCB, and drilled through the paper guide. On the copper side of the board I drew the connections with a marker and used an exacto knife to cut gaps in the copper. I widened these gaps with a scratch awl, and there were my traces (Fig. 6a).
For that personal touch, I painted my board black and wrote in the values of the parts on the face.
The transformers I had listed are ones I had laying around and PT2 was right at its amperage limit-- you might want to use 546-186B120 for PT2. Its secondaries (lugs 5 and 8) would be attached directly to the IEC and power switch in parallel with T1, the primaries (lugs 1 and 4, with 2 and 3 soldered to each other) making about 330VDC rectified. The extra voltage will make the valves love you so hard.
This will take a bit of stress off both power transformers, decreasing heat and increasing lifespan. 546-186B120 is not PC mounted but you can shorten the Power PCB and mount T2 in the new space. Moving T2 off board and feeding it from mains is the only change. I have both versions of the PCB posted, but the new version is recommended.
Step 3: More Metal Work
There are three remaining bits of metal to be contended with. The faceplate, a backplate, and a divider plate in the middle. The latter piece will hold the valves in place and separate the power supply, which will be emitting a lot of radio frequency noise and hum, from the valves, which will be making the good kind of noise. All of my metal will be coming from something I found in the trash. It's about one-sixteenth of an inch thick and so will not be taking any @#$% from you or your foot.
First I cut a piece 7.5 by 5.75 inches to use as a faceplate (these measurements are about 3/8 inches short of the inside measurements). I started here so I could position things inside the cavity and figure out the shape needed for the divider plate.
In keeping with the steampunk look, I wanted as many screws on the faceplate as possible (I thought about rivets but my anvil is 1600 miles away). I drew a line 1/8-inch behind the scalloped edge on the front side and drilled a 1/8-inch hole between each scallop. Then I drilled a 1/16-inch hole on the faceplate below each hole and tapped the faceplate to fit the brass bolts I bought from a hardware store. I only installed four bolts for the moment because I would need to take them out later when I painted everything.
Now, flipping the chassis over, I positioned the power PCB as close to the edge of the cavity as possible, figured out how much space I needed for the power switches, and drew a line down the faceplate. Then I laid the valve sockets (P-ST9-700 from Antique Electronic Supply) where I wanted them, leaving room to pull and replace the valves when they inevitably wear out. I drew a line at the sockets' bases, and from those two lines I worked out the piece pictured below.
The angle grinder made short work of that. Then I drilled two 3/4-inch holes for the valve sockets (with two 1/8-inch holes each for retaining bolts) and a 3/8-inch hole for wires to the footswitch (P-H498 at Antique Electronic Supply). The footswitch pulls double duty by also securing the arm of the divider plate to the faceplate. The divider plate is attached at one end by the bolts that hold the plate and square tubing together, and at the other end by two new screws. This arrangement blocks one of the holes--I just drilled through the offending spot and my ventilation remained unscathed.
The power PCB has four 3/16-inch bolt holes--these are duplicated in the divider plate.
The backplate will need to be periodically removed for maintenance, so I didn't want to go crazy with the bolts. It should be a structural element, so I didn't want to get tricksy with sliding releases and pneumatic actuators and string theory. I ended up with a simple 7.625 by 5.75-inch plate secured by four bolts. The bolts have large enough heads that I could grind in slots that could be turned with coins to make valve replacement a little more convenient. Of course, you are a good little musician who has packed a few screwdrivers and a soldering kit, right?
Step 4: Human Interface
I'll be installing a Fender Vibro Champ-esque effect in this chassis, but of course you can do whatever you want. For this tremolo, though, I needed three knobs and a footswitch.
The knobs are three electrical conduit box connectors I found at a thrift store. I love the weird-but-familiar junk I can find at places like that, and I have a small pile of things waiting patiently to become amplifiers. Last minute I found a chunk of a florescent light diffuser. I kind of hate the look of the diamond-patterned diffusers but holding this piece I found that the back side of it has more of a quilted look to it. I traced the opening of the conduit connectors onto the piece of diffuser and carefully cut it out with a fine-toothed jig saw. The diffuser was made of brittle plastic so I needed to support as much of the piece as possible while cutting it. I touched up the fit with a course metal file so that the diffusers would tightly fit inside the conduit connectors.
I mixed up a batch of one-hour epoxy resin (found at most hardware stores) and let it sit for about twenty minutes, waiting for it to thicken significantly (I just checked back periodically until the stirring stick could be held upright in the resin) so that I could pour a little into the conduit connectors but not have it seep through the imperfect seal. Once this cured I made a new batch of resin and filled the conduit connectors to just below the rim.
Once cured I drilled (with steady hand and vigilant eye) a 1/4-inch hole to take the shaft of the potentiometer. On the sides of the knobs I drilled and tapped a hole to place a set screw.
The knobs and such can be arranged almost any old way. I marked the areas on the faceplate I needed to stay out of and spent a while nudging my modified connectors around, imaging it in use and the different angles it would be seen at. I tried a few things, took a picture for posterity, slept, ate, stole glances, re-arranged, made a smoothie, then ended up with this. Awkward but structured. I like it, make your own if you don't (or do).
Step 5: Octopus!
The metal I used for the octopus already had red paint and plenty of scratches. I drew a mock-up of what I had so far onto the red sheet metal and had someone far more clever than me draw an octopus on it. Then using the angle grinder I cut out the bulk of one scalloped edge, then fine-tuned the edge with a file. When one edge fit I worked on the other scalloped edge, again fine-tuning with a file. Take light passes, constantly moving the file along the edge of the metal to prevent divots. Remove the material evenly, don't try too hard, and it'll carve itself.
Step 6: Finish Work
Time for paint! And we all know that the paint is only as good as the prep. First I removed the jacks, the strap bolts, and the faceplate bolts. The faceplate rattles around inside--it wasn't hurting anyone. Using a wire wheel, I removed any burrs, and I filled in the cracks at the corners with a thick five-minute epoxy. After sanding everything, I taped off both the heads of the bolts on the plate and the tapped holes for the strap bolts.
After two light coats of primer on the square tubing and the backplate, I sprayed on four coats of a textured black enamel. After a deep breath, I began final assembly.
I cut a piece of leather the same size as the faceplate, marked the positions of the pots and footswitch, and cut those out with an exacto knife, making the potentiometer holes the same size as their washers. I then glued the leather to the faceplate with contact cement. The face plate was attached with way too many screws to the square tubing.
The epoxy resin I used to fill the knobs is translucent. So I decided to light them from underneath with LEDs to make the knobs glow. One LED will turn on with the power switch, one will indicate if the tremolo is on, and the third will act as a constant current source on the oscillator section (do your reading). As the valve oscillates the LED will flash, giving you a visual reference. I just learnt about constant current sources from a gentlemen at the Hoffman Amps Forum. I can't say enough good things about DIY forums.
I drilled a hole the same size as the LEDs just above the potentiometers shafts. I enlarged these holes only half way into the metal with a bit the size of the LED's base. This way the LEDs fit flush with the back of the faceplate. You can see in the photo that the potentiometer washers needed a slight notch to make room for the LEDs.
The LED connections are detailed below, but remember that different types of LEDs require different value current-limiting resistors. Any LEDs should list their forward voltage and current, which you can use to calculate what resistor you need. The LEDs and their leads are held in place with a line of five-minute epoxy or hot-glue.
I found that not enough light gets through the resin... so I decided to drill additional holes around the edge of the knobs. As a hole gets closer to the LED, the spot gets brighter. A serendipitous bit of cool. I'll need to experiment with depth and technique, but I find this pretty exciting.
The divider plate needed to be warped slightly to fit it into the cavity but, once it was in, the power PCB was fixed in place on the plate, and the whole thing was bolted onto the chassis.
To provide a ground reference, a solid 12-gauge copper wire was attached to the middle lug of the footswitch and stretched to the back of the chassis, to be bolted to the tubular plate with a ring terminal. Most of the effect's components will be attached from lug to lug of components. The remaining connections will be to ground. This piece of overkill will be a sturdy place to attach any leads to and will provide a great ground reference.
The backplate was covered with a non-slip furniture foot pad. This will help keep the pedal in place and isolate it from vibrations off the floor. On the inside of the plate I drew the schematic for the power supply and the effect.
Step 7: Fin
Work methodically and keep checking your progress. Break the project into smaller pieces and be sure that they work separately before you make them play together.
I will be posting another instructable that further details the tremolo circuit, I just wanted to cover the huge hurtle that the chassis and the power supply provide. I hope that other people like this idea and run with it. I look forward to seeing their takes on the chassis and knobs, and to see the range of effects and amps people stuff inside of it.
Thanks for reading and let me know what you think of the project and my presentation.