DIY Modular Guitar Amp!

About the project:

Since I was a kid, I've had a guitar, but I didn't have a decent amp, and most of the amps available are either too expensive or don't suit my needs properly. With this in mind, I decided to do what any maker would do, design and build my own guitar amp. I wanted a powerful amp that could deliver some serious volume, great sound and the possibility to bypass the preamp and plug in an external FX pedal board, or any other audio source. Guitar FX modules/pedals are usually easy to make, and thus there is a great DIY community surrounding this subject. Because of this, I decided to make the design modular so I could easily incorporate and exchange different DIY FX modules. The amp is not hard to make, but it does require some basic knowledge about electronics, and electrical safety.Ths guide will include the instructions for using the same modules I used, but it is easy to exchange these for others. For a sound sample, please watch the video (Concentrate on how the amp sounds not how I play).

About the amp:

At this point, I have been using this amp for some time and in many situations, and let me tell you, this thing is great. The amp features a 68 watt power amplifier and a 12" Celestion speaker, which can deliver some serious power. The preamp section is comprised of several fx modules chained together. The modules I have currently installed are: 3 band equalizer (Tonemender), 2 channel distortion (Double D), and dual input mixer (custom design), and I left plenty of space in the top plate to add more modules in the future, like Reverb and Delay. The designs I chose for the modules were made by the guys at Runoffgroove.com, but they can be exchanged by any sort of DIY fx that you like. At the end of the preamp there is a custom dual input mixer that allows sound to either come from the FX chain or from a balanced XLR input. This way you can use the amp's FX or some external FX, or both at once. For more modules, check out DIYstompboxes.com and Runoffgroove.com (I especially recommend this website because they have sound samples so that you can easily compare and choose from their FX modules, and they often provide a breadboard layout as well). I always try to document my projects as best as I can and, when possible, make quality guides on how to make them, as I have learned a lot from the online DIY community and this is my way of retribution. This amp is desgined for guitars but, because of it's power, it works great for bass too.

Recommendations and safety notes:

Even though making an amp is really not too hard, it is important to note that this project involves working wit mains power and high voltages (the power amp uses 70 volts DC), so you must take safety measures and be sure that you understand what you are doing and the risks involved. For this, I recommend a series of articles by Rod Elliot (Great resource for DIY electronics enthusiasts):

• The Whys And Wherefores of Guitar, Bass and Keyboard Amps: http://sound.whsites.net/instamps.htm
• Electrocution & How To Avoid It: http://sound.whsites.net/articles/electrocution.ht...
• Audio Myths: http://sound.whsites.net/articles/myths.html
• Amplifier basics: http://sound.whsites.net/amp-basics.htm
• Audio Signal Mixing: http://sound.whsites.net/articles/audio-mixing.ht...

If you are really interested in understanding amplifiers and making your own, these articles will give you a very wide picture of the subject, and will help you stay safe and get an end result that satisfies you. Even though this guide will show you exactly how to make the Amp I made (which sounds great, at least according to me), I encourage you to dig into the subject and adjust the design to your needs and taste.

P.D. This instructable is in the Amps and Speakers contest so, if you consider it worthy, please vote for it.

To make things easier, I have grouped the reference files you will need as a zip download. Don't worry, the instructions for each part are detailed later. This file includes the following:

• Enclosure CAD for CNC manufacturing (Rhino file and DXF).
• Schematics (For each of the modules I used).
• Top & back plate layout/graphics (As an image and as an editable Excel file).

The enclosure is designed to be cut with a CNC machine and be assembled easily like a puzzle. However, the pieces can also be handmade (See pic 4 for all the dimensions). I chose to use 18mm Fiberboard because it is a cheap and durable material that yields a very nice texture, but you can make the enclosure out of any material, just make sure to adjust the joint dimensions to fit your material thickness.

Before assemblying, it is important that you thoroughly sand each piece to remove imperfections in the surface and ensure an even finish. Additionally, you must use a router to fillet (round) or chamfer (45 degree) the edges of the pieces, but be careful to only do the edges that are actually going to be edges in the finished product, so not the ones in the joints.

Once the enclosure is assembled, the way to secure everything together is via wooden pegs going both directions on each of the 4 short edges (See pic 7). The pegs are glued into a hole drilled by hand (It doesn't have to be precise as they will be practically invisible later). Once dry, they are trimmed flush (see pic 8).

Once the enclosure is assembled, it is time to give it a surface finish and add the protective hardware. To seal the wood, you should first apply a coat of clear lacquer, and then, to give it it's black color and bring out the texture of the material, apply 2 generous coats of black matt paint. (see pic 5 for a closeup of the finished texture).

Finally, add the corner protectors to all corners, the handle to the right side of the amp, and the rubber feet to the left side and bottom of the amp. The idea behind having feet on 2 sides is that you can either set it with the control panel facing the top, for normal use, of facing one side, in case you want to set it at ear level, and still be able to access the controls. Also, it allows the amp to be placed down while it's being carried from the handle.

The top plate is made of 1/16 aluminum plate and the back plate is made of 1/4 aluminum plate. The layouts for both are available in the downloads section (pic 1). To make them, first print each layout and stick them to the plates with repositionable spraymout (pic 2). Using the layout as a guide, create the holes using a drill (pics 3, 4 11,12) (drillpress recommended) and get them to shape using a file (pic 13). Also use the file to deburr and soften the edges (pic 14).

Once the holes are made, it is time to add the final graphics to the plates. For this, print both layouts with the exact colors and design you want on sticker paper (pic 5) and firmly stick them to the plates, ensuring they are aligned properly (pic 6). Next, add a layer of clear mica for protection (pic 6) and finally, use an x-acto knife or cutter to take out the paper from the holes (pic 8).

The finished product should look like pic 10 (top plate) and pic 17 (back plate). The design of the plates is intended to be as clear and self explainatory as possible for ease of operability, but it can easily be modified to suit other modules or have a different color palette/design scheme.

WARNING: Do not attempt to build the power supply if you do not know the risks involved and the safe procedures to deal with such voltages.

Making the power supply is probably the easiest part of building an amp, but it is also the most dangerous! The amp is directly fed from the mains (That is 120 volts AC), which can easily give you a significant shock, and outputs 70 V DC for the power amp, which can also be dangerous. Furthermore, the power supply includes some big capacitors which store quite a bit of energy even when the mains are disconnected. Because of this, it is important to never work on the power supply while it is plugged in, and always check that the capacitors are discharged before doing anything. To safely discharge the capacitors, use a 200 ohm 5 watt resistor connected between the positive and negative outputs of the supply.

Power supply:

• Standard 3 pin power cable (the one used in all PCs).
• Female connector for the power cable.
• 3-5A 25-0-25 Power transformer.
• 5A Fuse and Fuse holder.
• Power switch.
• 35A Bridge rectifier (For the main power circuit).
• 8A Bridge rectifier (For the ground bypass).
• 10 ohm 5 watt resistor.
• 2-4x 10,000 uF 50v Capacitors.
• 4x 100nf 50v capacitors.
• 2x 1000uF Capacitors (For the 9v output).
• 1x 9v Regulator.
• 1x 50 ohm 10 watt resistor (or equivalent network, to aid the 9v regulator in heat dissipation)

Now comes the most important part of the amp, the sound modules. The modules I used were chosen both for their good sound and for their simplicity, but there are plety of designs availabe on the internet to suit different sound tastes and more complex FX like reverb or delay.

To make each module, follow the schematics from the download section and make sure to add screw terminals for all connections to and from other modules. This way the amp is easy to assemble, troubleshoot and repair.

A breadboard layout is availabe for the Double D and Tonemender modules, but it is not necessary to follow that exact layout. It is important that each module is tested by itself before putting the whole amp together. Otherways it is impossible to pinpoint missconnections and problems.

The top plate is designed in such a way that the spacing between knobs corresponds with a discrete number of holes from a standard protoboard. This way, the potentiomenters can be soldered directly and serve to hold their boards.

To install the plates, align them properly with their respective holes and secure them firmly using screws around the edge, you want to use at least 1 screw every 5cm to be safe. On top of this, seal all around the edge with 100% silicon, and also seal all other internal edges of the amp, as we want to prevent any air leakage from the cabinet that might modify the sound.

After the plates are installed, the electronics are next, starting with the power supply and power amp. The power supply is attached next to the back plate with screws, and the power amp gets screwed to the heatsink which should be pressfitted into the hole next to the speaker (this hole should be modified to the dimensions of the heatsink you are using).

Next, the audio modules are installed on the top plate using their respective nuts. Finally, everything is connected together using wires as short as possible going into the screw terminals of each module. This is why it is important to add the screw terminals, as they ease assembly and repair.

Because it is so big and heavy, the transformer doesn't fit with all the electronics. Instead, it goes on the bottom of the amp, below the speaker. The mains wires come down through one of the front internal edges, and the transformer output goes up thorugh the other edge. Wires are to be held in place using zip ties and screw on cable anchors. The transformer must be firmly screwed in with all the possible screws.

Finally, once everything is connected, it is time to add the speaker from the front, blocking access to the electronics, and test the amp. Plug in an audio source and slowly crank the volume. If all goes well, you should hear the sound clearly and without noise. If no sound is emmited, it is likely that some connection came loose or was made incorrectly. If this is the case, open the amp and check that the audio chain is followed properly, that is, the input goes into the first module, the output from this goes to the next, and so on. If you are still having trouble, don't hesitate to drop a comment and I will try to help you.

Making this amp took a lot of research, as there are tons of possible designs with their own respective advantages and disadvantages, and it is hard to settle on one. Also, the design of many parts got settled on the go, but in the end I am very satisfied with the finished product as I think it really achieves all the goals I had; Portable but powerful, dual input, good sound, great looks, and ease of operability.

If you made the amp, please post pics of it, and if you just read the guide, please comment about it, as this helps a lot in making it better. I hope you liked the guide and, if you consider it worthy, please vote for it on the Amps and Speakers contest.