Introduction: A Tiny Bass Preamp and Effects Box: Black Ice, Electra Fuzz
In this guide I will show how you can make your very own bass/guitar pre-amplifier and effects box. I choose to make a hybrid effect box, which mixes the common “Black Ice” or “Electra Distortion” distortion effect with the “Bazz Fuss” fuzz effect. This is combo is great at making you sound like a rock/grunge star. Meanwhile the pre-amplifier makes the input much, much, louder for that added “oompf”.
Disclaimer: This is a very difficult project to attempt if building it to such a small form factor. I do not recommend trying to make it as small as I made it. Furthermore, rather than a definitive guide consider this instructable as more of a general guide. As the details of your build and your requirements will be subjective and different. I am not responsible for anything if you do attempt to build this and trying to put it into a small form factor breaks it or otherwise.
- 2x 3.5mm audio jacks
- 1x locking DPDT push-switch or stomp-switch
- 1x 1000mAh 4.2V lithium-ion (Li-Po) battery
- 1x TP4056 Li-Po charging module
- 2x 50k potentiometers
- 1x TDA2822 power audio amplifier IC
- 1x 100uF electrolytic capacitor
- 1x 470uF electrolytic capacitor
- 2x 100nF ceramic or film capacitor
- 1x 10nF ceramic or film capacitor
- 2x 10k resistors
- 3x diodes of any kind (silicon, germanium, LEDs? You choose and experiment, I used 1N4007s)
- 1x NPN transistor (any generic will do, I used a BC357)
- 2x potentiometer caps
- 1x injection-moulded project box
- 1x paper and printer to make panel
- Roll of thin double-sided tape
- Soldering iron, solder and flux
- Wire-wrapping-wire or other thin insulated wire
- [optional] wire-wrapping tool
- [optional] helping hands and/or magnifier
- Drill and/or hot knife
- Lots of time, patience and will-power.
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Step 1: About the Circuit(s)
The pre-amplifier is based on the TDA2822 amplifier chip, which is set up in bridge mode. This way there are two individual outputs; one of which goes to the analog effect circuitry while the other goes to the bypass/amplified output. This is the main component and reason for this build; it was originally going to be just this pre-amp, until the effects were added. I used whatever components I had in hand and worked, but since this chip is meant to be a power audio amp and not a pre-amp it still has some issues; mainly some distortion when the volume (on the bass guitar) is turned up too high, but nothing that effects normal functionality (perhaps this distortion could be considered a third effect!)
Both the distortion and fuzz effects are quite common and are centered around a common-emitter transistor amplifier. Hence why I was able to merge their circuits, adding a potentiometer to mix the amount of each effect. I recommend you to really play around with this circuit, trying different diodes, resistor and potentiometer values until you find what works for you. Oddly enough I also found that when paired with the TDA2822 pre-amp, this circuit has some random resonance that sounds like “wobble” which is an accidental bonus.
How it sounds:
In this step there is a video on how the different effects sound.
Step 2: The Schematic
Above is the schematic of everything that’s inside the box. The pre-amp is just a TDA2822 IC in a bridge
configuration, same as the datasheet (one slight modification: just replacing a 10uF capacitor for a 100uF one). The outputs of the pre-amplifier go through the DPDT locking push-switch which selects if the amplified or the amplified signal and the effects should be outputted. One potentiometer controls the mix between the distortion and fuzz effects and the other is a simple volume control. The whole circuit is powered off a 1000mAh lithium polymer battery, and turns itself on when a TRS connector is plugged into the input 3.5mm audio jack. I was originally going to use two AAA batteries, but the circuit has a bit high quiescent current draw at roughly 15mA, with this Li-Po it will last for approximately three days of continuous operation and it is rechargeable, with the addition of a simple TP4056 charger module.
Step 3: Experiment!
What you want from your effects box and how it sounds is very subjective so follow the schematic to
build a prototype on breadboard or similar. But change component values and see what sounds good to you. Remember and write down the setup that works to build it permanently later. Just a note: breadboard are horrible for audio circuits, as they have extra capacitance everywhere and pickup lots of interference, I recommend prototyping on vero-board/soldered-prototype-board using IC sockets instead.
Step 4: Layout
After you know which components you will need and what enclosure you will use, start by laying out
your biggest components in the enclosure and see what layout allows everything to fit. Potentiometers in particular take a lot of space, but are useful as ground buses, as their outer shells can be connected to ground. Make sure there are no sharp points of pressure on the Li-Po battery, as you would not want to puncture it! This step should give you an idea of how hard or easy the next few steps will be depending on how tight the space to build is.
Step 5: Creating the Holes
Now that you roughly know where your main components will be placed, mark out on your enclosure
(preferably using masking tape) where respective holes need to be drilled/made. I used a portable drill to make round holes and completed any other shapes with a combination of that and a hot blade (since my enclosure was plastic). I started by mounting the potentiometers and making holes for the TP4056 battery charger and the audio jacks. The potentiometers were a base for me to start building the circuits on top of.
Step 6: Circuit Construction
This is by far the longest and most labour-intensive part of the project. It took me around eight hours to
construct the circuit in such a small form factor. Simply follow the schematic and make sure you don’t miss any components or connections. Some tips n’ tricks to use are:
- You can use very thin “wire wrapping wire” to make delicate connections.
- If you have a wire-wrapping tool this will greatly help. (I love wire wrapping!)
- Superglue or BluTack can help hold components in place for soldering.
- Use snips to cut away excess leads from components after they're soldered in.
- Don’t throw away the snipped component leads as they can also be used to make connections.
- If you sand away the top coating and use plenty of solder-flux you can connect the shells of the potentiometers to ground and use that as a bus/connection-point.
- Make sure any wires that go in-between halves of your enclosure are long enough so that you can keep working with the enclosure open like a clam shell.
- Where possible avoid splicing wires, by having the right length in the beginning. If it must be done use heat-shrink tubing to avoid shorts.
- Don’t be afraid to use little bits of paper as separators to prevent shorts.
- Building the components in order of what “module” they belong to helps with form and restricting size.
- If building compact, utilize every space you can find.
- Once a functional section/module of the schematic is built, test it to make trouble shooting easier later on.
- Helping hands and a magnifying glass would be very helpful.
Step 7: Closing the Clam-shell
After carefully constructing the circuit and using a combination of cyanoacrylate super-glue, hot-glue
and whatever other adhesives you may have, carefully close your enclosure to finalize internal construction. You should test and troubleshoot your final circuit and make sure that there won’t be any shorts when the enclosure is closed before shutting it. Have patience to go back and tweak the position of things if they do not fit in the enclosure, the last thing you want is to break your working circuit now!
Step 8: Designing the Front Panel
Now for building the exterior, start by measuring the size that exterior panels/stickers should be. These
dimensions can then be put into any graphic design or word processing application to design their prints (I used Apple’s Pages). These can then be printed out in real size, cut and stuck to the enclosure with thin double-sided tape. Let me know in the comments what you use to make your panels.
Step 9: You Made It!
Congratulations! Give yourself a pat on the back as you’ve just made it through this instructable and
(hopefully) are now a new proud owner of a cool bass/guitar pre-amp and effects box (stomp-box?). Do comment and suggestions, ideas or questions you may have, and do post a picture if you make one too!
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