An Electric Musical Instrument 3D Printed Amplifier.

Project Definition.

I hope to make a printable amplifier for use with an Electric Violin or any other Electric Instrument.

Specification.

Design as many parts as possible to be 3D printable, make it stereo, use an active amplifier and keep it small.

Electronics.

Adafruit's Stereo 20W Class D Audio Amplifier is the perfect amplifier for the job. I searched for suitable speakers and found some small 4" 60W speakers. Add in a PSU and a 10k Potentiometer for volume control and I was set to get to work designing the speaker box..........

Please help support my work, your donations really do make a difference.
http://ko-fi.com/gregthemaker

Components & Hardware.

• Paired 4 Inch Vehicle Loudspeaker.
• 1/4 Stereo Input Jack.
• 12V 5A PSU.
• Adafruit Stereo 20w Class D Audio Amplifier - MAX9744.
• Adafruit Panel Mount 10K Potentiometer.

• 4 x 6mm M2.5 Socket Caps Screws.
• 32 x 12mm M4 Socket Cap Screws.
• 3 x Cable Ties.

• Optional Mini 3.5mm to 6.35mm 1/4" Gold Stereo Jack Headphone Adapter.

The eBay linked components are affiliate links.

Printables.

The Design files, including the STLs, are available from Thingiverse.

• https://www.thingiverse.com/thing:2466042

Choose a good filament to print the four STLs. I have chosen SpoolWorks Edge.

• spoolWorks Edge Deep Purple.
• spoolWorks Edge Clear.

by using the following affiliate links when making purchases. Thanks :)

eBay.com | eBay.co.uk | eBay.fr | Amazon.co.uk

Fusion 360.

To begin I am modelling the components in Fusion 360. That will help during the design phase with locating all the parts in the amplifier. If you are new to Fusion 360 There are numerous tutorials explaining how to use it.

Basics.

The amplifier is to hold within itself: two speakers, a PSU, amplifier electronics, cables, an input jack and a volume knob.

I started by copying the sketch used to model the speaker, making two copies and then separating them making sure to leave enough space between them for the 10k Pot.

I added circles for screws, and added outer circles to represent the screw caps.

Superior Sound Quality.

I wanted to have free movement of air around the two speakers so I drew air channels with front vents. Hopefully this will improve the sound quality. I'm not a sound engineer so this is basically guesswork!

After the sketch has been drawn I can extrude the model.

I create a space for the speakers, add openings for the air ducts, add the back, extrude holes for the screws and indent the front by 1mm so the speakers will sit flush to the front.

The Fascia.

The front fascia is extruded from the same sketch used to model the speaker box.

I added holes on the underside where the screw caps that hold in the speakers will be.

The Back.

I added a new sketch panel to the rear of the Speaker Box. It would have been possible to use the same sketch from before.

The Back is extruded 14mm and indented 5mm. Pillars are added for the amplifier board. Guides are added to keep the PSU in the correct position and channels added for cables ties so it is held secure.

A small channel is added on the side where the mains power lead will pass through.

Loudness.

Using the original sketch, cut-outs are extruded into both the fascia and speaker box. There is a hole which opens out into the rear of the speaker box for the wires. The front fascia has an enlarged hole for a printed volume knob.

The Volume Knob itself is extruded from a separate sketch.

Input.

You have the option of fitting either a 3.5mm jack, or a 1/4" Jack. I chose the larger 1/4 as this is the standard for electric instruments.

After measuring the input jack I have added a sketch at the rear of the speaker box. I used this sketch to extrude holes and clearances for the jack.

Printer Settings.

• 0.4mm Nozzle.
• 0.3mm Layer Height.
• 3 x Perimeters.
• 40mm/s Speed.
• 12% Infill.
• Sliced with Simplify3D.

Printing takes ~48 hours for all parts.

Assembly.

Assembly begins with installation of the 10k Pot into the Fascia. It is held in with a supplied nut and washer. Solder a wire to each of the terminals. Press the volume knob onto the 10k Pot from the front. It should turn freely.

Next solder speaker wire to the two speakers, the terminals should be marked + & -. It is important for sound quality that you get the connections correct on the speakers.

Feed the wire through the holes in the speaker box and secure each speaker using 4 x M4 12mm Socket Cap Screws.

Pass the volume control wire through the hole and secure the Fascia using 14 x M4 12mm Socket Cap Screws.

Soldering.

Adafruit's 20w Stereo Amplifier requires some assembly. There is an excellent tutorial on learn.adafruit.com which goes into detail and explains exactly how the amplifier needs to be configure for use with the 10k Pot.

https://learn.adafruit.com/adafruit-20w-stereo-audio-amplifier-class-d-max9744

When soldering the input jack it is very important that you make a note of each connection. Incorrectly wiring the jack to the amplifier can break it!

Final Assembly.

Mount the amplfier to the back panel, secure the PSU in with two cable ties and then connect the wires. I put a single cable tie onto the A/C lead to stop the cable from being pulled out.

Connect the cables to the amplifier board ensuring you have the right polarities!

Secure the back onto the speaker box using 10 x M4 16mm Socket Cap Screws, taking care not to trap any of the wires.

Plug In.

The speaker box will work fine with any electric instrument. If you chose the optional 3.5mm - 1/4" adapter jack then you can even plug in your phone too!

Plug in the input, turn on the power and listen!

Electric Violin.

The impetus behind the want to design an amplifier is the F-F-Fiddle Electric Violin by OpenFab PDX.

http://openfabpdx.com/fffiddle/

I followed their build guide and printed the parts using the same materials to match with the speaker box.