There's been a renewed interest in stereo systems. Things like turntables and tape players have caught people's fancy once again. Tangible media has something a download will never have, it's an item you can display, hold in your hand, or physically gift to another fan of the format. With this renewed interest comes a need to have the hardware to play your media on.
The renewed interest has caused prices of once ignored gear to be driven up. Unlike an i-something dock, stereo systems can become rather elaborate multi piece devices. At bare minimum you have an all-in-one unit that has a turntable, tape player, and receiver in one box with two speakers. That's still three pieces of gear and those all-in-one systems were generally of poor quality. There were exceptions to this but they were few and far.
Being at one time a starving student and tinkerer myself, I can appreciate a cheap solution. That's were this instructable comes in. We're going to hack an i-something dock (ipod, sansa, what have you) into a stereo amp to drive external speakers. Spend less on your amp if you don't need house shaking volume and you'll have more for your speakers or source equipment.
Step 1: Tools, supplies, warnings, and DANGER
What you'll need to complete this task.
1) stereo i-something speaker dock like an i-home or similar
2) soldering iron, electronics grade rosin core solder, and knowledge of it's use
3) some basic hand tools like screwdrivers to get into the dock and wire strippers/cutters
4) a pair of 2 wire or a 4 wire speaker terminal strip and a 2PST switch (both items optional if being really frugal)
5) a dual 1/8" stereo plug cable and music player (for testing before and after)
6) 1/8" stereo plug to rca cable for connecting external sources like tape machines and other full size stereo gear to your finished project
7) basic wiring knowledge
You will need to open up the i-something dock in this project. There is a risk of electrical shock. If you're dock uses a wall transformer or power external power pack, the shock can be a tingle. If your dock has an actual wall cord hanging out of it, you can be killed if you do something careless. If you are uncomfortable working with live electronics it is suggested you seek assistance from a knowledgeable geek.
Finally, soldering irons melt metal. You can get burned, burn other people, or things if you're not careful. Once again seek help from a knowledgeable geek if you're not sure how to use a soldering iron. If you plan on doing more tinkering, by all means learn to solder as you'll be doing lots of it.
Step 2: Ipod dock into a stereo amp?
Believe it or not, the biggest shortcoming of those little desktop docks is their speakers (pic 1). Little speakers are cute. They swing madly in their little boxes trying to reproduce music as best they can but there's really no replacement for displacement. You don't see musicians toting around little clock radio sized speakers do you?
The tech behind the amps inside those little docks has actually gotten to a point where they sound better than any all-in-one entry level stereo ever did. The better docks easily exceed the output power of all those Soundesign and Emerson all-in-one units that used to flood department stores up until the early 1990's.
How does the amp in the little box do it? Most modern day consumer electronics like ipod docks, cellphones, tablets, and even flat screen tv's have switched to class D audio amps. These are basically an audio amp on a chip and due to the way it works, they are super efficient and very crisp sounding. Super efficient translates to lower power consumption and little in the way of power wasted as heat which means no need for a big hunk of aluminum to dissipate heat. Little amp, good sound, little wasted power.
In pic 2 we have a 1960's era small stereo amp, next to it is a postage stamped size circuit board. What do these have in common? They have basically the same output power, aprox 3 watts per channel. The old amp uses traditional transistor circuitry. The little board is a very efficient class D PAM8403 amp board. The miniturization is incredible. It's no slouch on sound quality either as long as it isnt pushed into distortion.
In pic 3 we have the PAM8403 amp chip on a cassette tape for size comparison.
The downside to these class D amps is when you turn them up too loud they distort very harshly. Don't drive them to distortion and they can sound amazingly good.
Step 3: So let's get started and find a donor dock!
First you need a victim to hack. Thrift stores, yardsales, fleamarkets, and friends are all good sources for an unwanted dock. You want one that's working and only has two speakers. Why only two speaker models? Because they are stereo. There are single speaker docks and even some that have some sort of surround setup. Skip those and look for only a two speaker model.
The next most important thing to look for which fortunately most docks will have is an AUX jack. This is a line level input. This is were you connect an external non "i" device to the dock and where you will be connecting your audio gear to.
What docks to get? The i-home docks are well made and common finds but any two speaker dock with an AUX jack that works is a worthy candidate. Some docks even have FM radio tuners which is an added bonus for our needs. Make sure it works and plays reasonably loud in it's unaltered state. If it looks and feels real chintzy, skip it.
Additionally, some docks have the ability to run off batteries. This can be a bonus as it will allow you to take your hacked stereo amp on the go.
Let's test the dock and make sure it works. Try it out using it's ipod connector or the AUX in jack. You will need the correct cable and a music source to test via the AUX jack. Got anything? Yes? Good! You are done with this step.
No? OK, got more to test. You are sure you turned the volume up... right? The ipod jack could be broken which is common and why these docks often times get tossed. Some docks have FM radio capability, try that. You don't need clear audio, even radio static will let you know both channels on the dock's internal amp work. Still no love? The AUX in jack is your last hope for a quick test. You will need a dual 1/8" plug stereo cable and a portable music source to test via the AUX in.
If the dock is not working as intended it could still be usable for our purposes but you shouldn't be paying more than a few dollars for it as it's basically trash to the average person at this point. More in depth testing will be needed!
Step 4: So you found a victim, Let's dig in.
You're going to need a set of jewelers screwdrivers to get into most of these devices. They commonly use small Phillips head screws to hold them together. Some Apple products will have "special" screws which are easily defeated by "special" tools available online for getting into Apples "special" devices.
Once in, you are looking for the wires that run to the speakers. There should be a pair of wires going to each speaker. That's were we will be tapping in to drive our external speakers.
What's all the other stuff in there? You'll have the amp chip, a chip that talks to the ipod or whatever mp3 player the dock was designed for, maybe some voltage regulation stuff, and maybe a radio tuner if the dock is so equipped.
A money saving tip!
Look for a dock with a busted ipod connector. those delicate little connectors are often the reason docks get tossed. You wont be using that part for this hack so it doesn't matter. $5 or less is what I have found docks with bad ipod connectors for.
Step 5: Test the dock
What if you have a dock that doesn't work properly? Let's dig a little more into it...
In pic 1 you see the dock wired up and stripped of it's case. I took my board completely out of the case but you don't need to go that far with disassembly. You really just need access to the internal speaker wiring.
If you find a dock that powers on but there is audio on only one channel or none at all everything is not lost. Some folks like to blast these until they quit with no regard for longevity. The amp chips in them are actually quite smart at protecting themselves. There's a good chance the electronics may be fine and the little speakers just gave up. Wiring up a random known good speaker in place of the docks internal speaker is a good way to test for dead internal speakers and a working amp. This will require get into the dock.
You will need a known good speaker, speaker wire, a dual 1/8" plug stereo cable (the size commonly used on almost all portables), and something with a 1/8" headphone jack that plays music for this test. With the dock opened up and access to the wiring terminals on the built in speakers (pic 2 is an example), turn on the music player with the 1/8" stereo cable hooked to it, play something, and plug into the AUX in jack on the dock. Turn on the dock and turn the volume up. Take the wires you hooked to the known good speaker and touch the other ends to the two wiring terminals on the dock's speakers. If the amp works, you should have audio.
Step 6: Wiring the switch and the speaker jacks
So we're up to the part were we wire in the switch and speaker jack. This will require soldering. If you don't have soldering equipment or prefer not to deal with that, you can just bring the speaker wires straight out the back of the unit and bypass this step. It will look much nicer and last longer though if done with a switch and speaker jacks. Pic 5 shows how you can extend the speaker wires without soldering and just cut a notch in the case to bring them out.
If your dock has dead internal speakers, you can skip the switch portion and just extend the internal speaker wires out to reach the terminal strip and wire that in place. Skipping the switch is also an option for those that don't care to use the internal speakers any longer.
For those doing the full Monty, onwards to wiring in the switch!
Here, we will be using a 2PST switch, also known as a DPST switch. Something similar in appearance to pic 1 offered by MCM electronics will do. It doesn't need to be a large high current switch. A 2PST is a double pole, single throw switch. That means it can make or break two electrical connections at one time. What this will do is make or break the connection to the internal speakers. The class D amp chips are fairly resilient and have numerous protection circuits. They can tolerate being operated with no load or even a short circuit. They will shut off in a worst case scenario to protect themselves.
On traditional amp circuits, you can damage the amp if you connect more than one pair of speakers at one time and it presents too low a load to the amp. Since we don't have that concern here, we just need to be able to turn the internal speakers on and off without worry about whether or not you have the external speakers wired in.
In pic 2 you see the back of a large automotive grade 2PST switch. I used this just for illustration purposes as it's a little easier to see the contacts but you don't need something so large for our project. The wiring is fairly straight forward. You will be interrupting one wire to each internal speaker and running it through the switch.
Pic 3 is a schematic for the wiring. I apologize for it's crudeness but all the info is there. When reading a schematic, a line from one device to another is a connection. If the line makes a little "hop" over another line it means that those two are not connected, they are just crossing past each other in the drawing.
The amps speaker wires will branch out to the external speaker jacks. The external jacks will be powered on all the time. The switch is just going to interrupt power to the internal speakers giving you a way of shutting off the built in speakers when you are running external speakers. Why not run both? You can but remember you have a low power amp to work with. Why waste the juice on the lousy internal speakers?
In pic 4 you see an ideal candidate for a 4 wire speaker jack. This one is available from MCM electronics as well as many other suppliers. Some car stereo shops that do custom work even have these for sale for a dollar or two. This is what you will be mounting on the back of the dock. You will need to find a place where you can cut a small section of the case out with wire snips and mount the jack strip. Keep in mind the jack strip gets screwed down so take into account the length of the screws that come with it. You don't want the screws shorting things out inside the amp when you reassemble.
Pic 6 shows a 2 wire speaker jack mounted on the back of another dock amp project I did. You can use 2 of these and have one on each side of the amp if you like or use a single 4 wire strip. the end result will be the same, 4 connection points. You can use diagonal cutting pliers to trim the plastic where the case halves meet on your dock and make space for the terminal strip. To make the screw holes use a small drill or if you're tool box challenged, a jewelers screwdriver heated with a lighter or the soldering iron makes quick holes in plastic. Make sure and use something smaller than the diameter of your screws so they actually have some plastic to bite into and hold. Remember, if it melts plastic it burns fingers so be careful.
Step 7: What speakers to drive and what to expect.
In the pic you see a large speaker and next to it is a tiny little silver speaker. Unfair comparison? The little speaker came out of a dock like the one we are modding for this instructable. The big speaker came from an old stereo console. What do they have in common? Both were designed for roughly the same amplifier power. Obviosuly the bigger speaker will move more air and thus be more efficient.
Speakers have 3 important ratings.
1) frequency response - how accurately they cover the range of human hearing
2) power rating - how much power they are designed to handle
3) sensitivity - how much audio they produce at 1 meter when being fed 1 watt of signal
Good speakers make or break an audio system. Your hacked up audio dock can sound amazingly good if connected to a good set of speakers. It might sound so good you can even mess with your audiophile friends by hiding it and playing the "guess the amp" game with them. Conversely, an audio amp costing thousands can sound terrible when connected to lousy speakers. Speakers are the most important thing in any audio system. Keep that in mind.
The same places you'd look for the junked dock for this project can be a source of good speakers. Some very general guidelines for sizing up unknown speakers are size, heft, and brand. Good speaker cabinets sound solid when you smack the sides of the cabinet with your knuckles. They shouldn't sound hollow like an empty box. Good speaker cabinets are heavy due to the dense materials they use. Efficient speakers are big. The goal is move more air which translates to more sound. Finally brand is a good indicator. Speakers made by companies that survive solely on selling speakers are probably going to sound decent if not amazing.
Why am I talking about premium speakers on a hacked up ipod dock build? Because great speakers can be found for less than $20 a pair if you cruise enough yard sales, thrifts, and fleamarkets. I've run super efficient theater speakers of an old panasonic cheapo boombox and left my friends dumbfounded at how good and loud it sounded. Bad speakers make everything sound bad.
If you are really bent on building and learning more about speakers, check out the diyaudio.com forums. Lots of tinkerers there willing to share knowledge and experience.
Now with our little dock amp we don't have much to work with power wise. Expect 3 watts to each speaker. This is why speaker efficiency is important. Don't let the low power rating dishearten you though. Most TV's have about the same amount of power going to their built in speakers and look how loud they can get. It's not going to be block party loud but plenty for playing at enjoyable levels.
Just remember that speakers make or break any audio system.
Step 8: What can I drive my amp with?
AUX in jacks expect to see line level audio signals. You will need a cable like the one in the pic. it's a 1/8" stereo plug to rca cable. These are common at most electronics stores and online for just a couple of dollars. Line level is what you will get from the output jack on a cd player, cassette player, reel to reel deck, tuner, 8 track deck, and the audio line out on a computer. You can also use the headphone output on a portable player or computer to drive the AUX in on the dock amp. The dock should have a volume control. This will still function as intended as we haven't touched that circuit.
What about playing records through it? If you have a good turntable, it will require a preamp to bring the really low output of the turntable to line level. These turntable preamps can be found online for about $20. Lesser quality turntables sold for folks wanting to convert their LP's to mp3's usually have the preamp built in or use a ceramic needle / cartridge assembly that has line level output but aren't the best sounding. As with all turntables, worn needles or bad records sound bad no matter what you use to amplify them. If you're a musician on a budget you can run the line out of an audio mixer into the dock amp and that will work too.
I hope you had success and saved a useful device from the landfill while learning a little bit. I used my hacked dock to run a pair of theater speakers for a few days while working on this instructable and it's amazing such a cheap little box can actually sound good when paired with decent speakers.
Enjoy and rock on!