Introduction: Digital Delay Pedal

About: My name is Randy and I am a Community Manager in these here parts. In a previous life I had founded and run the Instructables Design Studio (RIP) @ Autodesk's Pier 9 Technology Center. I'm also the author of t…

Building guitar pedals is a time-consuming, often frustrating, and expensive process. If you think you will save time and money by making your own digital delay pedal, I highly advise you to read R.G. Keen's page on the economics of pedal building. However, if like me, you are obsessive, enjoy messing around with electronics and want to make something that looks and sounds uniquely your own, continue reading ahead... just don't say that I didn't warn you!

Follows are detailed instructions on how I made my own digital delay pedal. I must admit that I used a laser cutter as an integral part of the process, but I feel most of the tasks that I am using it for can be performed with many more modest tools. My focus of the Instructable is not so much in the assembly of the circuit, but the assembly of the case, as this is where the real crux of the problem lies. Cramming a lot of things into a little enclosure is not particularly easy. Yet, it's my hope that these instructions will help in some way to simplify the process.

Short Delay:

Long Delay without Feedback:

Long Delay with Feedback:

Step 1: Go Get Stuff

You will need:

(x1) "BB"- sized Steel Enclosure
(x1) PT2399 Echo Processor
(x1) TL072 low noise op amp
(x1) LM7805
(x3) 100K potentiometers
(x1) 50K potentiometer
(x1) 5K potentiometer
(x1) PCB
(x1) DPDT stomp switch
(x1) SPST toggle switch (SPDT okay)
(x1) Power jack (with cut-off)
(x2) 1/4" mono jacks
(x5) Knobs
(x1) sheet 1/16" santoprene rubber (McMaster-Carr 86215K22)
(x1) sheet 1/8" cork

(x1) 100uF
(x3) 47uF
(x1) 4.7 uF
(x6) 1 uF
(x3) 0.1 uF
(x2) 0.082 uF
(x3) 0.0027 uF
(x2) 0.01 uF
(x1) 100 pF
(x1) 5 pF

(x2) 1K
(x11) 10K
(x2) 15K
(x1) 100K
(x1) 510K
(x2) 1M

(Note that some of the links on this page are affiliate links. This does not change the cost of the item for you. I reinvest whatever proceeds I receive into making new projects. If you would like any suggestions for alternative suppliers, please let me know.)

Step 2: The Schematic

My schematic is largely (read: almost entirely) based upon Casper Electronics' EchoBender pedal, which is in turn largely based on Tonepad's Rebote 2.5 Delay pedal, which is in turn, more or less, based upon the example schematic in the PT2399 datasheet. Having breadboard all three, I personally can not hear a significant difference in sound between the Casper Electronic version and the one on Tonepad, which some people say is superior sounding (the one in the datasheet just sounds flat). The nice thing about the Casper Electronics version is the inclusion of a feedback pot, which gives a really full sound to the echo effect.

The things that I have changed are a few mildly significant resistor and capacitor values. The biggest difference is that I have removed the "long delay" distortion pot. This potentiometer is basically forcing the chip to under-sample the input to create a longer delay and, in my opinion, doesn't sound very good. If you like under-sampled, long-delayed, audio, by all means throw in a large (1M) potentiometer in series with the delay pot. As you may have also inferred from this, the longer the delay, the less clear the output signal; so be warned that even the "short delay" starts to degrade when cranked up all the way.

For redundancy sake, I have redrawn the schematic. I have put three image notes on my schematic to indicate parts of the circuit that have changed. The schematic drawn by Casper Electronics is much more clear and I recommend you mainly go by that one.

Step 3: Breadboard the Circuit

Build out the circuit on a breadboard.

Why breadboard?

There are a couple of reasons:
1) To make sure you get it right in the first place. There is nothing worse than soldering a circuit permanently in place to find out it doesn't work.
2) This method allows for experimentation. For instance, should you not like how it sounds, you can easily swap out parts until you do.
3) You can easily expand upon the circuit.
4) It is also quick to do and if you discover that you don't like the circuit at all, you didn't just waste a lot of time soldering.
5) It gives you a reference to go by when you finally do decide to permanently solder it together.

Step 4: Solder the Circuit

Once you are sure the circuit works on the breadboard, solder everything, but the jacks, potentiometers and switches, to a printed circuit board. Pay careful attention to your connections.

If you have enough parts to do so, it is recommended that you leave the breadboard intact as a point of reference. It is wise to only disassemble the breadboard after you are absolutely sure the soldered circuit works.

Step 5: Make Rubber Brackets

Using the attached files, cut out the bracket patterns into a 0.2" sheet of rubber. I used a laser cutter, but you can probably get the same results with a sharp utility knife and some careful tracing.

These two pieces will go between the potentiometers and the case, and the switches and the case. They will function to prevent the body of the potentiometers and switches from rotating.

Step 6: Stencil the Front

Download the attached file, zero your enclosure in the laser cutter and stencil the image onto the front of the case. Do one strong pass or two medium passes. You want to etch until you can start to see the metal of the enclosure.

If you don't have a laser cutter, print the file onto adhesive paper, stick it to your enclosure and cut it out with an Exacto knife

Step 7: Paint

Stir your black enamel well (as it has a tendency to separate) and then apply a coat to each of the words etched on the top of the case. Wait for it to dry and apply a second coat. Then, wait for it to dry once more and move on.

Tip: To keep your brush from drying out between coats, you can leave it submerged completely in the enamel.

Step 8: Drill

Clamp your case in a drill press vise. Be sure to use some sort of uniform padding like a sheet of cloth or, in my case, a thin cork mat. Be sure to properly clamp the vise or secure it otherwise to the drill press.

Using a 1/2" drill bit, align the bit to the center of the marking for the foot switch button and then drill.

Replace the 1/2" bit with a 9/32" drill bit and repeat the process of aligning and drilling to make 5 holes for the potentiometers.

Step 9: Peel

Peel away the painters tape and carefully use an Exacto knife to pick or gently scratch away any bits of stray paint around the lettering.

Step 10: Drill Some More

Now, we need to drill holes on the side of the case. Two of the holes will have a 3/8" diameter and be for the audio jacks (on the left and right sides). The other two holes will be for the DC power adapter jack and an on/off switch (on the back side). For these two holes, you should obviously use drill bits appropriate for the size part you have (I recommend drilling test holes in scrap material first). As you can see, I also made an extra hole for a switch I didn't end up using (you can ignore that unless you have a use for it).

To figure out where to drill these holes I temporarily installed some potentiometers, then using tape stencils and the parts to be installed, I figured out the exact position of the hole on the inside of the case. Once I had this in place, I lined up an identical stencil on the outside of the case. The theory here is that the hole on the inside matches the hole on the outside, such that when you drill through, your part should fit in precisely where it needs to be.

I found what works best in this case is if the 1/4" audio jacks are situated between and "above" (when looking down inside the case) the two rows of potentiometers (and also far enough from the edge to account for the lip of the lid). The switch and power jack position are less critical, but should also be situated "above" the potentiometer.

Once all of your tape is in decidedly place, drill your holes.

Step 11: Etch Again

This time around, we are doing things a little backwards as you may notice, we first drilled the holes and now we are etching. I decided to do it this way as to ensure that I drilled holes that aligned correctly with the potentiometers on the inside of the case.

Anyhow, simply place a piece of paint over the hole and use a pencil or blade to poke through the tape and expose the hole. Next, place the box in a drill press vice. Lower the bed of your laser cutter about one foot and then place the whole shebang inside. The easiest way to do this is turn off the x/y axis lock, turn on the red dot pointer, move the laser head to where you feel the zero-point should be and then reset the laser's home. Then, with a little bit of trial and error and few pieces of tape, you should be able to get the right alignment.

Etch using the following settings:

Power: 50
Speed: 100
Passes: 5

If you don't have a laser cutter, make some stencils as before and affix them appropriately to the case.

When you are done, repeat the process of painting, peeling and picking away excess paint.

Step 12: Cork Lining

Line the lid with a sheet of cork or other thin insulator. This will give the circuit board a surface to rest upon that isn't conductive and prevent it from shorting out.

The attached file can be used in a laser cutter and produces a shape that accounts for the lid's inner lip and screw holes.

I have attached the cork to the lid with some spray glue. In retrospect, I should have lined the edges with blue tape before spraying as I needed to wash the spray glue off afterward (which was a pain in the neck).

Step 13: Pots and Switches

Install your potentiometers and switches inside the case using the rubber brackets to hold them in place.

Don't forget to align the potentiometers to their appropriate labels.

100K - Dry Volume
100K - Wet Volume
100K - Repeat
50K - Delay
5K - Feedback

Step 14: Wire the Front Panel

It is time to wire up the potentiometers using stranded wire. The right pin on each should all be connected together as ground. The other pins should be connected as per the wiring diagram below.

I recommend using different color wire for each pin not connected to ground. For this assortment of wires, I used the wiring harness from a broken computer power supply. This gave me many different colored wires to chose from.

Step 15: Wire the Power

Wire the power jack so that it is tip positive. In other words, the red wire from the 9V battery should be connected to the center pin and the black battery wire should be connected to one of the pin that gets disconnected when the plug is inserted.

Connect another black wire between the unused pin and ground on the circuit board.

Also, connect a red wire from the red power pin to the center pin of your SPST power switch. Connect one last red wire to the terminal that makes connection to the center pin when the switch is toggled to the "On" position.

Step 16: Connect the Front Panel

Connect the wires from the potentiometers and the power switch to the circuit board as appropriate.

Step 17: Wire Everything Else

Lastly, you need to wire up the DPDT stomp switch and the input and output jacks.

If your case is conductive, you only need to connect one pin from the jacks to ground. The other pin will make a connection through the case.

That said, make sure you connect the input and output jacks appropriately. In case you don't know what appropriately is, the input and output pins should be connected respectively to the center pins on the DPDT switch. One outside pair of pins should be connected to the circuit board (paying careful attention to "In" and "Out"). The other set of pins should be simply tied together for true bypass.

Step 18: Finishing Touches

Now is time to put on the finishing touches.

Use a wrench without serrations to tighten the nuts and tightly fasten the potentiometers, switches and jacks onto the switch.

Plug in a 9V battery.

Put everything inside the case, put the lid on, make sure you can insert plugs into both jacks unimpeded and then screw the case shut.

If you haven't done so already, put on the potentiometer knobs and tighten their set-screw.

Lastly, you may want to consider putting some self-adhering rubber feet on the bottom.

Step 19: Plug and Play

Plug it in and rock out.

If rocking out is not working, DON'T PANIC!

Open the case back up and debug the problem.

Here are some tips for debugging:

1) Is it turned on? Well... turn it on.
2) Does the battery have charge?
3) Are there any bridged connections on the PCB?
4) Do all of the connections match the schematic?
5) Have you wired the switches correctly?
6) Have you routed the cable properly from IN to OUT?
7) Is the volume turned up on your guitar and amp?
8) Is your amp even on?
9) How about the volume on the pedal?
10) If its on but not delayed, have you tried stepping on the foot switch?

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