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Description
“Four Way Stereo Audio Line Splitter w/ Adjustable Gain Two-Stage Amplifier” (tha’s what that meaningless jumble of letters really says)

None of my electronics (laptop, mp3, CD, etc.) has the juice it takes to drive a good set of headphones. I already have a stereo line splitter, but all it does is divide the signal, which leaves me wondering, “What the hell happened to all the volume?” Anyway, I finally decided to build my own line splitter with a built-in amplifier, and since I was building it, I’ll take it one step further: I doubled the number of outputs of a conventional splitter. The original schematic was waaaay too squashed up to be presentable for the ‘net, so when my dad’s broadband service completely failed (which also took out the TV), I decided to redraft the damn thing and make it more presentable. There are still some eraser marks from text problems and when I added that li’l switch in there. At any rate, I'm happy with how this schematic turned out, and if you wanna make your own, then get "Electronics for Dummies" and learn the bare basics, and have fun!

The circuit calls for only two dual OP Amp IC chips, and each chip amplifies one channel of sound. The total gain of each half of the circuit will range anywhere from 9-16 dB, which means that the gain for each individual Amp must be 3-4 dB. The ratio of each pair of resistors (the first one at the input and the second one being the feedback) determines the gain. As for the batteries, the design will call for two AAA batteries, and either one 3V watch battery or two 1.5V watch batteries. The AAA batteries will supply the necessary amperage the circuit needs and the watch batteries will provide a far more than necessary voltage boost. In the end, there should be enough gain to drive four sets of headphones very well. As for those two capacitors, their future in the design is questionable since any DC offset noise in audio out signals is already filtered out by the electronic device in question.

Anyhow, I’m calling this little monster “Medusa” for a very good reason. It’s gonna be a nice little rectangular box with five little wires snaking out of it. One wire plugs into the electronic device. The other four are what the headphones plug into.

Now, for those of you that are electronically dyslexic, these next few paragraphs will provide not only links, but also descriptions of what each part should (or will) do…

Let’s start from the left and work our way right. C1 and C2 are capacitors. They’re supposed to act as DC offset noise filters. Don’t ask me how that works because I honestly can’t tell you. Like I said earlier, they may be dropped from this schematic altogether.

R1-R8 are resistors. They are the most important (and usually most abundant) parts of a circuit. In some, they prevent excessive current (I.e. amps or milliamps) from obliterating the fragile components. In this one, they provide the necessary values and feedback to calculate the gain, or increase of power, of each OP Amp. The resistor that is at the input (the – sign) is only part of the equation. The other resistor that goes from the output (the tip of each triangle) back to the input provides feedback. It essentially returns the signal. The equation G=1+R2/R1 determines gain where G is the gain, R2 is the feedback resistor, and R1 is the input resistor. R4 and R8 are different from the others, though. How? They’re potentiometers. A potentiometer (or pot in electronics slang) is basically a variable, or adjustable, resistor. R4 and R8 are feedback resistors in this case. Now, if I want a gain of 3 in just one stage of amplification, then the resistance (measured in ohms) of R2 must be approximately two times the resistance of R1, and don’t forget about that 1+!

Now, on to those li’l triangles. They’re labeled IC1A, IC1B, IC2A, and IC2B. This is a small code I came up with. “IC” denotes the symbol’s status as a part of an integrated circuit, or IC for short. If you look in a computer, all those little black rectangles you see with the millions of little strips of wire poking out of their sides are IC’s. “1A” and “2B” determine the chip number and the component number as well. Given this numbering, this circuit calls for what appears to be two, dual OP Amp IC’s. An operational amplifier, or OP Amp in electronics lingo, is a very useful tool. In this case, they are being used as amplifiers to boost a signal. They are also being used in the “inverting mode.” Basically, they flip the signal upside down. In this case (being that we’re dealing with acoustics rather than data), that doesn’t matter in the slightest. Each IC amplifies a separate channel of audio streaming. By channel, I mean left or right because we’re dealing with stereo sound. The reason I did NOT use specific IC ID numbers is because each different type of chip and each different brand uses a different numbering system. The ID of an NTE Electronics CMOS dual OP Amp will differ from a Texas Instruments TTL dual OP Amp. Of course, the differences between CMOS and TTL are a whole other story.

I’ve already mentioned the batteries, and S1 is the switch. J1-J4 are the audio out jacks. Basically, they’re exactly like that little hole you plug your headphones into. They just pack a bit more juice than normal.

Description
“Four Way Stereo Audio Line Splitter w/ Adjustable Gain Two-Stage Amplifier” (tha’s what that meaningless jumble of letters really says)

None of my electronics (laptop, mp3, CD, etc.) has the juice it takes to drive a good set of headphones. I already have a stereo line splitter, but all it does is divide the signal, which leaves me wondering, “What the hell happened to all the volume?” Anyway, I finally decided to build my own line splitter with a built-in amplifier, and since I was building it, I’ll take it one step further: I doubled the number of outputs of a conventional splitter. The original schematic was waaaay too squashed up to be presentable for the ‘net, so when my dad’s broadband service completely failed (which also took out the TV), I decided to redraft the damn thing and make it more presentable. There are still some eraser marks from text problems and when I added that li’l switch in there. At any rate, I'm happy with how this schematic turned out, and if you wanna make your own, then get "Electronics for Dummies" and learn the bare basics, and have fun!

The circuit calls for only two dual OP Amp IC chips, and each chip amplifies one channel of sound. The total gain of each half of the circuit will range anywhere from 9-16 dB, which means that the gain for each individual Amp must be 3-4 dB. The ratio of each pair of resistors (the first one at the input and the second one being the feedback) determines the gain. As for the batteries, the design will call for two AAA batteries, and either one 3V watch battery or two 1.5V watch batteries. The AAA batteries will supply the necessary amperage the circuit needs and the watch batteries will provide a far more than necessary voltage boost. In the end, there should be enough gain to drive four sets of headphones very well. As for those two capacitors, their future in the design is questionable since any DC offset noise in audio out signals is already filtered out by the electronic device in question.

Anyhow, I’m calling this little monster “Medusa” for a very good reason. It’s gonna be a nice little rectangular box with five little wires snaking out of it. One wire plugs into the electronic device. The other four are what the headphones plug into.

Now, for those of you that are electronically dyslexic, these next few paragraphs will provide not only links, but also descriptions of what each part should (or will) do…

Let’s start from the left and work our way right. C1 and C2 are capacitors. They’re supposed to act as DC offset noise filters. Don’t ask me how that works because I honestly can’t tell you. Like I said earlier, they may be dropped from this schematic altogether.

R1-R8 are resistors. They are the most important (and usually most abundant) parts of a circuit. In some, they prevent excessive current (I.e. amps or milliamps) from obliterating the fragile components. In this one, they provide the necessary values and feedback to calculate the gain, or increase of power, of each OP Amp. The resistor that is at the input (the – sign) is only part of the equation. The other resistor that goes from the output (the tip of each triangle) back to the input provides feedback. It essentially returns the signal. The equation G=1+R2/R1 determines gain where G is the gain, R2 is the feedback resistor, and R1 is the input resistor. R4 and R8 are different from the others, though. How? They’re potentiometers. A potentiometer (or pot in electronics slang) is basically a variable, or adjustable, resistor. R4 and R8 are feedback resistors in this case. Now, if I want a gain of 3 in just one stage of amplification, then the resistance (measured in ohms) of R2 must be approximately two times the resistance of R1, and don’t forget about that 1+!

Now, on to those li’l triangles. They’re labeled IC1A, IC1B, IC2A, and IC2B. This is a small code I came up with. “IC” denotes the symbol’s status as a part of an integrated circuit, or IC for short. If you look in a computer, all those little black rectangles you see with the millions of little strips of wire poking out of their sides are IC’s. “1A” and “2B” determine the chip number and the component number as well. Given this numbering, this circuit calls for what appears to be two, dual OP Amp IC’s. An operational amplifier, or OP Amp in electronics lingo, is a very useful tool. In this case, they are being used as amplifiers to boost a signal. They are also being used in the “inverting mode.” Basically, they flip the signal upside down. In this case (being that we’re dealing with acoustics rather than data), that doesn’t matter in the slightest. Each IC amplifies a separate channel of audio streaming. By channel, I mean left or right because we’re dealing with stereo sound. The reason I did NOT use specific IC ID numbers is because each different type of chip and each different brand uses a different numbering system. The ID of an NTE Electronics CMOS dual OP Amp will differ from a Texas Instruments TTL dual OP Amp. Of course, the differences between CMOS and TTL are a whole other story.

I’ve already mentioned the batteries, and S1 is the switch. J1-J4 are the audio out jacks. Basically, they’re exactly like that little hole you plug your headphones into. They just pack a bit more juice than normal.