By Ben Adler
Skill Level: Intermediate to Advanced
Assembly Time: 2-3 hours
|Do you love your music? Do you wish you could listen and share your music wherever you go? With this mini speaker system project, you can listen to music whenever you want: your dorm, your cubicle or at the beach. This is a great introduction to circuit systems, featuring an introductory amplifier circuit, a filter circuit and a simple enclosure. When you're done, all you need to do is add a 9V battery, plug in and play!|
Drill and drill bits
Strong glue or epoxy
|1||22 Gauge Hookup Wire (Threaded)||818-5*|
|1||8Ω Speaker (treble)||TV-4171A-R|
|1||8Ω Speaker (bass)||FR-05202-01|
|1||Audio Amp Single Speaker 1 Channel||LM386N-3|
|1||8 Pin IC Socket||6000-8DW-R|
|1||Toggle SPST On/Off Switch||T100T1B1A1QN|
|1||9 Volt Battery Snap||BAT-SNAP-4|
|1||9 Volt Battery||ALK 9V 522|
|1||3.5 mm Male Audio Jack||AP-340-R|
|1||6' 3.5 mm Male/Female Audio Ext Cord||255-265|
|1||2.5" x 4.5" Protoboard||PCB-858-R|
|4||4-40 Machine Screw||28643|
|4||4-40 Hex Nut||36012|
|1||6" x 3.5" with 1.875" Core||H2851-R|
|In audio terms, an amplifier does exactly what its name suggests: it amplifies the current. That is, it takes an electrical signal and makes the signal stronger, and in the end, louder. An electrical signal that is passed by an amplifier comes out louder through the speaker than one that hasn't been amplified. Also, because the signal is strengthened by an amplifier, you can play that music through higher resistant speakers. This amplifier is a solid-state-hi-gain design and is intended to run through an 8 ohm speaker. As the amplifier schematic was originally designed by Ed Vogel and Blind Lightnin' Pete from MAKE Magazine, all credit goes to them for the amplifier design (below).|
|Before we begin to build the circuit for the amplifier, let's take a look at the protoboard. This board has a specific layout that should be understood before beginning to solder (unless you enjoy desoldering). The topology of this board is such that there are four columns in which the outer two columns are connected in rows, and the inner two columns are connected in rows. This should be taken into account when building the circuit.|
As you can see in the photo above, there are four columns on the protoboard with the inner columns appearing slightly lighter than the outer columns.
On to the construction of the amplifier circuit!
Step 1: Soldering the ConnectionsPlace solder on the IC DIP socket in a way that none of the rows are connecting. This means that you need to place the IC DIP socket so that the pins are parallel with the columns and the IC DIP socket crosses the gap between one of the outer and inner rows. Also note at which end pin 1 will be located. If you don't do this, your circuit may not work due to putting the op amp in backwards.
|Begin to build the circuit as described in the schematic. One trick I found particularly helpful was to make the circuit pin by pin. That is, I worked on the circuitry connected to pin 2 of the IC DIP socket, and then pin 3 and 4, then 5, etc.|
Step 2: Getting the Circuit OrganizedBefore I began constructing the rest of the circuit, I wanted to do some organization to make the rest of the circuit much easier. I labeled the outer columns of the last two rows (and soldered them together) as negative and the inner columns of the last two rows as positive. Then I attached the corresponding battery leads to these areas. This way, whenever something needs to be connected to +9V, I could hook it up to the '+' area and whenever something needed to be connected to -9V (including anything that needs to be grounded as the -9V will serve as a ground in this circuit), it will simply be hooked up to the '-' area. This method of organization works well for me, you may have another way that works too!
Step 3: Connecting the Rest of the PinsConnect both pins 3 and 4 to ground. As you can see in the picture below, when pins 3 and 4 needed to be grounded, I hooked them up to the '-' area.
|Work on pin 5 of the circuit. The wire that is coming from the circuit is the output lead. Also important to note is that it is connected to the center pin of the rheostat.|
|Work on pin 6 of the circuit. It is important to note that the switch is connected to the '+' area and the other to the '+' end of the capacitor. The end doesn't particularly matter because a switch merely completes/disconnects a circuit. For now, don't solder the leads to the switch, as you will need to screw them into the box later. What I did was tie the wire to each end of the switch so that I can remove them later.|
At this point, we've constructed an amplifier circuit. If we hook up an 8Ω speaker, we can blast some awesome tunes through it. But, could we do better? One way to increase the quality of sound through a speaker system is by using a filter circuit.
Step 5: Building the Filter CircuitA filter circuit (also known as a crossover) basically splits up a signal into ranges of frequencies. This way a speaker would only have to play a smaller range of frequencies, leading to a higher sound quality and longer life. Another way to think of it is that it allows speakers to "specialize" in a range of frequencies. That way a speaker built for lower frequencies wouldn't have to play treble or a speaker built for higher frequencies wouldn't play bass.
Fortunately, building the filter circuit isn't nearly as complicated as the amplifier circuit. This passive filter circuit of my own design is supposed to have a cutoff frequency of about 820 Hz. It is also supposed to have an impedance of 8 ohms. That way when each filter is in line with its respective speaker, the total impedance will be 16 ohms. When these are wired in parallel, the total impedance will be 8 ohms, which is what the amplifier is designed to support.
A tip to building this filter circuit is to designate an area that will serve as a ground, and then wire this area to the '-' area. It's also a good idea to make one filter in the inner columns and one filter in the outer columns.
A. Set up and solder the inductors.
B. Set up and solder the capacitors. Make sure that the long end (+ end) of each capacitor is in front (the current runs through the + end to the – end).
C. Set up ground wires connecting components to the ground.
D. For the high pass filter, set up two leads that will ultimately go to the speakers. Repeat for the low pass filter.
E. Connect the output of the amplifier to each filter.
Below is a picture of the final filter. The high pass filter is in the inner columns and the low pass filter is in the outer columns.
Step 6: Adding the SpeakersA speaker is what ultimately ends up playing your music. It operates by having a coil of wire and a magnet. When alternating current goes through the coils, it generates a magnetic field which is either repulsed or attracted to the magnet's magnetic field. This pushes the coil up/down, which makes the attached cone move up/down. This creates a sound wave by displacing air. When it reaches your ears, you hear some awesome tunes!
All you need to do to set up the speakers is to connect the speakers to their respective filter. The rectangular speaker should be connected to the high pass filter and the circular speaker should be connected to the low pass filter. Below, you can see the low pass filter's speaker on the left and the high pass filter's speaker on the right.
Step 7: Enclosing the SpeakersThere are many purposes to an enclosure in any speaker system. However, the primary one for this speaker system is to give the two speakers a place to rest and direct the sound waves.
A. With a marker, trace the outline of the speakers on the inside of the case.
B. Create holes well inside these outlines by using a drill. You can also use a soldering iron. However, make sure you do not breathe in the fumes. Melted plastic fumes are toxic and dangerous. Also make sure you clean off the soldering tip once it cools using soap and water.
C. Use a little bit of glue, epoxy or superglue around the edges of the speakers. Glue the speakers on. I cannot stress this enough: Watch the edges of the speakers. If any glue gets in the cone, the speaker is likely to be ruined.
D. Wait an hour for the glue to dry.
E. Remember earlier when we decided not to solder the switch or the potentiometer? This is why. Get out your drill (or soldering iron if an appropriate drill bit is not accessible) and drill three holes in the lower-back end of the enclosure. Make sure not to drill too big of a hole. Screw in the 3.5mm audio jack, the potentiometer and the on/off switch.
F. Rewire and solder the on/off switch and potentiometer.
G. Wire the outer lead (long lead) of the audio jack to the input wire and solder. Then wire the two inner leads of the audio jack together and wire them to the '-' area.
H. Take out your sharpie and mark the four holes which will hold in the circuit board. A good strategy is to hold the circuit board against the inside and poke the holes at the edge of the circuit board with the sharpie.
I. Drill these holes.
J. Using your screwdriver, screw the circuit board into the back using nuts to lock it in.
K. Attach the knob to the potentiometer sticking out the back. Also attach the 3.5mm audio connector cord.
L. Now connect your battery and plug in your IC to the IC DIP socket. Make sure your IC pin 1 matches your IC DIP socket pin 1.
M. Close the top and screw it all together... your speaker systsem is now complete!
|Feel free to play your iPod, mp3 player or CD player through this system and rock out to some tunes! If your audio eventually becomes distorted, it is likely because the battery needs to be replaced. Simply unscrew the top and take the old 9V battery out of the snap and plug in a new one. Re-screw the lid and enjoy!|
Ben Adler is currently a student at Rice University. While generally undecided about his major, he plans on majoring in some type of science or engineering. Ben is an audiophile and loves to recycle unwanted speaker, to make his own speaker systems.
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