Someone emailed me yesterday asking about one of my FrankenFiiO mods. Since I’m here to help (that contact link on the top isn’t just a gimmick) I took the thing apart, took some pics and made a schematic on how to mod this awesome little headphone amp.

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