DIY Stereo System

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 Ever want a great stereo system but know you are just better than buying one? If you are like me and have more time than money, it may worth looking into. Because building a stereo system isn’t as hard as it seems. Now I’m so 1337 yet that I can make one out of tubes, so solid-state will have to do. (Only an audiophile can tell a difference in sound quality anyway)

First you have to find 3 loudspeakers, two 8 ohms and a 4 ohm one. If you can’t find a 4-ohm another 8 ohm will work too. The two 8-ohm speakers are for the left and right channels and the 4 ohm is for the optional subwoofer. To stay within my budget I went to the dump and found 5 good loudspeakers. If you don’t have any luck at the dump you can try finding some at an online auction.

I’m assuming you know how to put a schematic together so build these. Remember to make 2 amplifiers if you want stereo. The power supply is run off a wall wart which should supply 14-24 VAC @ 1 A. If you only have DC wall warts you can try to modify one. Locate the secondary winding (where power comes out) and remove the circuit and all components. The transformer will now supply AC.

 

I used the TL-071CP op-amp, but a two-in-one package might be something to consider. Also I used two fixed value resistors instead of a volume pot. That way both channels will always play just as loud. You will notice significant distortion at high volume, so it’s a compromise between volume and sound quality. But this circuit is the best one I could find when it comes to heating, power usage and sound quality. I set the volume low on the circuit and turn it up loud on my computer, that way I get no audible distortion.

 

This amplifier is just like the channel amps, expect it filters out everything except bass. Us this excel sheet to determine the cut-off frequency. Or use this formula;

1.4142 / (2*3.14*C1*R1)

 The values are in Ohms and Farads. The 220nf cap is C1 and R1 is 2* the 4.7 resistors. The 100nf cap has to be half the size of C1. I know I’m not clear, so just stick to the circuit, the cutoff frequency is at 137 HZ.

 

This is a type of voltage doubler which will give you a split rail power supply. The 78xx and 79xx are voltage regulators. The higher their voltage the more volume you’ll get out of the amplifier. Make sure they are a few volts under what your AC supply gives, and under the operating voltage of the op-amps you choose. Between 12 and 20 volts is a safe range.

Once you finish building those you should have something like this.

 

Next up is the control panel which is important for any DIY stereo system otherwise some fool might think you bought it from a store. I didn’t have metal or metal-working skills at the time, so I improvised. The picture is self-explanatory.

 

Next up wire everything together and hope it works. If so, its time to start wrapping things up. Decide which speaker should be the subwoofer, and open it up. The only way to enter many loudspeakers is through the large bass speaker, which can be screwed off. Inside you will find fiber-glass insulation which is not good. Discard it carefully, or save it so you can put it back in the speaker afterwards. It may or may not affect the sound.


This is what you will end up with. You can see the built in cross-over filter inside, just cut it off from the speakers. Depending on your skill you will have something that looks better or worse than this.


Using professional connectors and hook-ups for the AC, IN, OUT, and a nice locking switch and LED is a must. The LED is not really that bright.

 

And there you go! This “guide” is far from complete, but is should give you a good push in the right direction. This system is not hi-fi, but good for a beginner in DIY audio.

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