A resistor adapter is simply a small adapter between an MP3 player and headphones that has a resistor on each of the sound channels. The reason for this is to increase the resistance of the headphones, forcing the MP3 player to work harder to drive them. Many players (with the Cowon D2 being the most known player with this issue due to its powerful amp) can’t perform well with low impedance headphones such as lightweight 32 ohm headphones or earphones that can go as low as 16 ohm. Beside the issue with the volume control not being sensitive enough to work well at volume levels as low as you might get in such cases, the amplifier in the player simply can’t perform as it should under such low loads.  This issue, called roll-off, mostly affects bass and the effect can be seen very easily in this RMAA graph (courtesy of elektrokrishna.com).

As you can see, the bass frequencies are seriously compromised at 16 ohm load (left side of the graph – it should be flat). At 80 ohm it’s a lot better, but only at 300 ohm is it really as flat as it should be (technically lower than that but there’s nothing showing a load between 80 and 300 int hat graph). This issue is fixed by simply adding a resistor adapter in between the player and the headphones, upping the load on the player and giving you better sound quality (a lot more bass in this case) – granted your player has a roll-off problem.

Tutorial

First off you need to gather parts. You need two identical resistors, and by that I mean IDENTICAL resistors. Two resistors that are said to be 40 ohm, might as well be 38 and 42 ohm, so I urge you to use a multimeter and measure the resistors until you find two that match. As long as they match eachother, it will be fine. Depending on your headphones and their impedance, you need to balance the added impedance versus the loss in battery life (don’t panic; higher volume level caused by the harder-to-drive headphones means a slight loss in battery life, obviously) and the fact you still need to be able to turn the volume up high enough for you to hear (so no 1 kohm resistors, people). I usually recommend about 40-50 ohm for 32 ohm headphones, as 80 ohm is a nice level – even if it doesn’t make the curve above completely flat. If you have a D2 or another player with a powerful amp, you could easily do 100 ohm for the adapter. The parts used aren’t exactly that expensive (not if you buy in bulk, anyways, one by one they might be) so why not make several to experiment?

When you have your resistors, you also need a short wire, a female 3.5mm (1/8″) headphone jack, a male 3.5mm headphone jack, some wide heatshrink, a hot glue gun and a soldering iron (the picture shows two of everything since I made two adapters while taking the pics, a custom cable job for a buyer – see the “custom cables” link at the top!). Of course this is what I used in this particular tutorial, as with all tutorials I do I can’t show you every single design you can do for a resistor adapter, I can only show you one and then you have to take the methods I use and implement them on your own adapter. In other words, you don’t need to match the parts perfectly with what I use. For example, this tutorials shows how to make an angled adapter – you might want a straight one, or one with a short extension cord- etc.

For the 3.5mm male headphone jack, I do recommend the ones I use here – they are simply old earphone plugs split open and stripped to the bare plug. These are excellent low profile plugs and far better than the DIY ones you get at “The Shack” because they are small and cheap. You can also get these from cheap audio cables sold at DealExtreme.

First off, solder the wire to the ground channel of your 3.5mm female jack. On a male 3.5 mm jack, the ground channel is the root of the plug, the right channel the middle of the plug, and the left channel the tip of the plug. You have to extrapolate this to the female jack to see what solder point is what channel. The ground channel is normally in the logical place, but on some connectors – like the ones I use here, the middle solder point of the female jack is actually the left channel and vice versa, as inside the plug there are metal springboard-like connectors that go in opposite direction of the each other, making the channels switch place inside the connector. This can be seen on picture 7 below where you can see inside the connector as the top plate is clear plastic. Bottom line: make sure that what you think is the correct solder point for a specific channel actually is just that.

Using the hot glue gun, glue a resistor to each side of the female jack.

Cut the ground channel wire to length and solder it to the ground connector on the male 3.5mm jack like the picture shows.

Hot glue the male 3.5 mm jack to the female 3.5 mm jack, pointing as shown above. Notice the insides of the female connector and how the springboard-connectors make the channels switch place. Your 3.5 mm female jack might be like this, or it might not. You have to find that out or you risk mixing up the channels.

Solder the resistor legs to the male 3.5 mm jack. Again, make sure you match the channels properly – the tip of the male plug is the left channel, which means that the tip of the solder-end of the male jack is also the left channel. Right is in the middle on both as well. Match this with the correct resistor.

Test that it works. You can use this file to check that you got the channels right (or find out which is which on the female connector if you haven’t already). The first 5 seconds of the audio file plays using both channels, the next 5 seconds is left channel only, while the last 5 seconds is right channel only.

Encase the entire thing in hot glue. This insulates against short circuits and makes the whole thing a lot more sturdy. Please don’t skip this step because it looks ugly, your adapter will self-destruct after 5 minutes of use.

To make it a bit better looking, you can use heatshrink. I found that 20 mm (diameter) heatshrink worked well for the two adapters I made here. I recommend getting heatshrink that’s narrower than what you need and then use needle-nose pliers to extend it. That way you get better shrink ratio to better cover the less-than-symmetric adapter you just made.

That’s it, you now have a resistor adapter. If you’d like, you can take a look at the video below. It’s very old, from the first resistor adapter how-to I made. Still, might be useful in some way (though I doubt it).

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The FrankenFiiO (V1-V2 link, V3-V4 link) mods were a series of mods I did to the FiiO E3 $7 headphone amp (black, white) about a year or so ago. It started with some rather ugly, bulky devices and ended with a sleek, wooden amp with it’s own analog volume control – the V4. The V4 was the one the guy in the email wanted to know about, so the schematics and tutorial shows how to wire that setup. However, the box design is more or less the only thing different between the versions, so the basic concept applies no matter what you want to do with it.

Parts needed

Obviousely you’ll need an E3. You’ll also need some wires, a stereo potentiometer designed for audio use (there are a billion different ones so pick one that fits your project), two female 3.5mm (1/8″) audio jack connectors and some wires. You also need some way of turning the thing on and off – the default way of turning an E3 on and off is to insert a headphone plug in the headphone port. A method that is even less usable when you’re going to rewire everything. You can therefor either buy a power button, or get a stereo potentiometer with a built in on/off feature. These work by having a on/off clickswitch when you turn the volume all the way down (these are very common in cheap portable radios etc so you’ve probably used one and know what I’m talking about). There are also 3.5mm jacks that will do the same as the stock FiiO jack and turn it on when a plug is inserted. Whatever floats your boat. In any case, if you’re not using the stock on/off method, you will also need a 3.5mm male hadphone jack – just cut it off some crappy headphones or acquire one in some way or another.

Wireing

The wireing is pretty simple and straight forward. First off, get rid of the casing so only the PCB (motherboard) is left. The cut-off headphone jack should be inserted into the headphone-out on the E3 PCB (you can cut off as much as you want of what sticks out, but be sure to not short circuit the 3 channels in the jack). This is necessary to have the E3 always be on so that we can wire a new power switch directly from the battery or it wouldn’t work since the E3 would think no headphone was connected and not turn on).

Each end of the E3 PCB has an audio jack. Take notice of which one’s in and out (by looking at the casing). There are basically 3 SEPARATE solder points on each jack – one on top, one in the middle and one at the bottom. On a male 3.5mm jack, the tip is the left channel, the middle is the right channel, and the base/root is the ground channel. When you insert the male plug into a female connector, that is of course flipped so the left channel (that the male tip touches) is farthest from the jack hole. The right channel is still the middle, and the ground channel is closest to the jack hole. It’s important to know where each channel is within the plug, as some female connectors are rather deceiving when it comes to this; the ones I used on my E3 mod had a transparent top plate where you could luckily see that the middle solder point actually was the left channel and vice versa as they switched places inside the connector itself. Point being: make sure you solder the left channel wire to the left channel connector, not just what you THINK is the left channel connector – and so on. The external female connectors shown in the schematics show the internal connectors, not the external, as they vary depending on what connectors you use- so pay attention.

When you have the audio connectors sorted out and know what solder point is the correct channel, the rest is pretty simple. For the input jack, you simply solder a wire each on the left, right and ground channel connectors on the stock E3 audio connector and then solder the wires to the corresponding sodler points on one of your external female audio connectors – as shown in the schematic.

The output jack is a bit more tricky, but it looks more complicated than it is. You basically wire it the same way, but on the way from the stock audio connector on the PCB to the new audio connector the wires have to “stop by” the potentiometer so you can control the output volume. A stereo potentiometer will in most cases have 6 solder points – 8 if it has a built in on/off switch like mine (and the one in the schematic). The 6 ones that are clustered together is what you need to look at first. If you hold the potentiometer with the solder points pointing towards you and the volume knob shaft pointing to your right, then you’ll have a matrix of 2×3 solder points. The bottom two solder points is the audio input for each of the left/right channels, the middle two are the audio outputs for the left/right channels and the top two are the ground pins. As shown in the schematic, you solder a wire from the left channel of the stock female connector on the PCB to the left (or right, but lets keep it clean) bottom solder point on the potentiometer, then a wire from the left middle solder point on the potentiometer and to the corresponding left channel solder point on the new external 3.5mm female audio connector. Then you do the same thing for the left channel. For the ground channel, just solder the wire from the stock connector’s ground channel to BOTH of the top solder points on the potentiometer and then to the ground pin on the external 3.5mm connector (you can do this with one wire if you wish, just removing some insulation in the middle and soldering that to the potentiometer pins. The schematic shows all of this.

The last thing to do is to add the power switch. Solder a wire on each of the battery connectors. One of the wires you connect directly to the battery (make sure you connect to the right end of the battery by looking at how it would sit in the stock battery holder), and the other one you solder to either of the two solder points on your power switch (in my case one of the two remaining pins on the potentiometer). Then you solder a wire from the other solder point on your power switch and to the other end of the battery. As for the battery, it has to be 1.5V – but if possible you should cram as much in there as possible. You can do that in several ways: by using a bigger batter, such as a AA, C or even D battery instead of the AAA, or by connecting several batteries in parallel (NOT series). For example, if you have a flat box that will fit several AAAs but no AA, you can use several AAAs by connecting the positive ends of each batteries to one another and the same with the negative ends (NOT postivie to negative as that will increase the voltage, not capacity). An AAA battery has approximately 1000mAh, an AA battery 2000mAh, a C battery 6000mAh and a D battery 12000mAh, but the actual capacities vary by brand. A crappy AAA can have 500mAh or less and a good D battery can have 20000mAh. If – for example – you used 2 lithium AA batteries with a capacity of about 3000mAh (those fancy expensive Energizer ones) that would give you 10 times the battery life of one crappy AAA battery. You get the point. Cram as much capacity in there as you can, but make sure it’s 1.5V.

That’s it. I explained this in more detail than necessary so here’s the short version: Put a cut-off 3.5mm connector into the input jack to override the built in on/off feature, rewire the audio-input to a new connector, do the same with the audio-output but wire it via a potentiometer. Rewire the battery and add a power switch.

Case

I’m not going to show you how to carve a wooden case like the one I made as it’s one of those things that require skills, not a tutorial. Either you know how to do it, or you’re too inexperienced with the tools needed to do it even if I told you. Amps fit into a variety of things from mint boxes to random plastic storage boxes or tuna cans. Use your imagination

When you’ve been a blogger for a few years on several sites, things start to get mixed up and forgot. Between various forum threads, anythingbutipod articles, pocketables articles, my olg blog and this blog I have perhaps 3-400 non-news posts lying around and I don’t remember them all. That was also the case with this post, until a nice guy from Greece emailed me a couple of days ago asking about it. I remember I’d done a car audio guide somewhere, but couldn’t for the life of me find it – so I asked the guy for a link to my own post. Turns out it was a really old post from the days when I manually updated my captain-odegard site, which is several years ago now (having had this site and a wordpress based version of the old site in between). It’s a somewhat useful article, so I thought I might as well throw it up here and update it slightly.

Car audio guide

When it comes to car audio systems, people are normally far behind on technology compared to what their home or portable setup is. People with a top notch mp3 player might still use CD’s in their cars, simply because they don’t know how to implement their mp3 player in their car system. Here are a few tutorials on how to make it all work.

Video Setup

Portable DVD players are often bought by parents to make kids keep quiet during drives. Using such a player by default is easy, and doesn’t need any explaining. Many mp3 players however have the ability to output video through a TV out cable. Zune HD, Cowon S9/D2/A3/O2, iPod/iPhone etc are some examples of players with this feature. To hook these up to a screen in the car, you of course need a screen. Many(/most) portable DVD players have AV-in capabilities, and you can also buy standalone LCD monitors if you prefer so. You have to get a AV-out cable that work with your player, and in most cases there isn’t a standard cable that will work – you have to get one fpr your specific player. There are also different types of cables, most importantly component and composite cables. Component cables have 5 RCA connectors (3 for video, 2 for audio) and will only work on larger or more advanced monitors and not smaller ones such as portable DVD players. Composite cables have 3 RCA connectors and will work for portable DVD players.

Picture: Portable DVD player with included TV cable and Cowon D2 with its proprietary TV cable

It’s all in all pretty simple, colors kinda takes away the guessing game of what cable goes where
Note that you have to choose AV in on you DVD player and AV out on your video player, the method for doing so depends on what player you have. Normally it’s a hardware button on the DVD player and a menu option on the video player.

Power Setup

No fun with flat batteries… Unfortunately, a lot of players can’t charge and play at the same time. Either way, there’s basically two ways to charge your player in the car: Use a specially made car charger, or use a USB adapter. Which of the two you can use depend on whether the player supports USB chargers or not. Read more about USB charging in my USB charging guide on Anything but iPod.

Audio Setup

This is what most people want, and what surprisingly few people know how to do: Get an mp3 player to work in the car. There are basically 4 ways of doing this: You can buy a car integration system, a car stereo with USB or line-in, you can use a cassette adapter, or you can use a FM transmitter.

Car integration systems

This would be the rich iPod user’s best solution. As far as I know, few or no other players have this option – maybe with the exception of the US-only Zune. Basically it’s an expensive way of integrating your iPod into the car audio system. I think it’s a waste of money and not applicable to very many, but if you really have an iPod and a brand new car you can google it yourself and find out more.

USB/line-in Capable Car Stereo

This is by far the best solution, audio quality wise, but it requires that you buy a new stereo for your car (unless your current one has this option of course). A line-in capable car stereo is very cheap, for USB it’s slightly higher I believe, and of course it all depends on your country.

Line-in is basically a 3.5mm or 2.5mm female audio jack input. It’s normally located on the front panel of the car stereo, and is often referred to as “aux” (auxiliary input). All you need to connect to your player is a line-in cable. Many companies try to sell line-in cables marked for specific players, but it’s just the same 3.5mm male to male cable you can buy in pretty much any electronic store. If you have a 2.5mm input on your car stereo, you’ll need a 2.5mm male to 3.5mm male cable instead (the 3.5mm plug goes into your player), or a 2.5mm to 3.5mm adapter. With a player connected through line-in (remember to select aux input on the car stereo), you control the music on the player and not the car stereo. Some people use a wired remote with this method, and there are also kits (for iPod of course -.-* ) that are designed to be put on the steering wheel and allow you to operate the player that way.

With USB capable car stereos, you don’t control the music from the player. Instead, the car stereo uses the player as storage unit only, meaning you can just as well use a USB stick or a memory card if the unit has a memory card reader. For the USB method to work, the player must be UMS, meaning that it pops up on the computer as a removable drive. It must also be able to work without full USB power available – as a flash drive and not a charging-needy MP3 player, as most of these USB ports don’t provide that much power (voltage is of course the standard 5V of USB, but it might only provide 100-200ma vs 500ma on a computer. No this won’t break your device even if it doesn’t work). No software dependent crap (iPod or Zune, or MTP devices) will work with this, unless you assign a part of the player to work as a portable hard drive and copy music files on there, but that wastes space. To connect the player, you just plug the player into the USB port or USB cable converter that comes with the stereo, depending on what solution your stereo uses. When you’ve done that, there should be a USB mode somewhere on your stereo. Frankly, this is kidna useless as you might as well buy a cheap flash drive to use for your stereo. Connecting your player through line-in is much better since you then control everything on the player and you can use all the player’s features.

Cassette adapters

If you have a CD car stereo without USB or line-in, and want to use your mp3 player, you’re actually better off installing an old cassette car stereo. Cassette adapters don’t work as well as line-in, but they work a lot better than FM transmitters. Basically, a cassette adapter looks like an audio cassette with a 3.5mm audio cable attached. You put in the cassette, press play, and connect your mp3 player, and that’s it, no hocus pocus about it. Cassette adapters can be bought in a lot of electronic stores, or you can pay 1/5 the price and buy from China.

Bluetooth

Some newer car stereos have built in Bluetooth, allowing you to wirelessly connect to the car stereo with a Bluetooth capable player. Sound quality wise this is abou tthe same as cassette adapters as Bluetooth isn’t perfect, so if line-in is available that is the better solution. However, Bluetooth might allow you to use the car stereo as a hands free.

FM transmitters

The last, and worst sounding solution, is the almighty FM transmitter. What this does is basically transmit your music to the car radio on a specified FM frequency. All you do is plug it into the player, turn it on, select a frequency and tune to that on the radio. Sounds too good to be true? It is… First of all, interference is a MAJOR problem. If there are many radio channels nearby, finding an unused frequency might be hard enough, and on top of that pretty much everything seems to affect the signal. The closer the transmitter is to the radio antenna, the better signal you’ll get.

There are about as many FM transmitters as there are mp3 players. You have proprietary transmitters like for the iPod/iPhone, and you have universal ones with 3.5mm jacks. You can also get transmitters that are specifically built for cars – plugging directly into the cigarette connector, and even transmitters with remote control. The later actually function as mp3 players, and have a USB port or card reader as well as audio in. The way the USB and memory card function works is just the same as USB and memory cards on car stereo systems, they use the connected devices as memory only. The audio quality of these transmitter players isn’t top notch, but you loose so much quality when transmitting through FM anyways that it doesn’t really matter. Here are some from China.

Some new car stereo’s also have bluetooth capabilities, which means you can transfer music to the system if you have an A2DP capable music phone or player. However these players should also have line-in, which is a much better solution that anything wireless.