Universal Earbud/Headphone Volume Control

So I bought a PMP (Portable Media Player) from Hong Kong so i could play my NES games with the on-board emulator wherever was convenient. Long road trips, flights, waiting rooms, etc. are places that I like to kill time with portable media but the only trouble was that the on-board emulator only had one volume......MAXIMUM. My earbuds of choice didn't have adjustable volume so i needed a solution to turn the game music down a little, I ended up coming up with the 3.5mm Earbud/Headphone Volume Adjuster.

Note: Turns out I'm not the only one with this idea, I did a quick search on Youtube and found this tutorial! I was even able to find a few commercial versions of this idea out there but they were $10-20.

Step 1: Tools & Materials Needed

Materials you will need:

- Safety Glasses, Safety First!
- 3.5mm Male Stereo Audio Jack
- 3.5mm Female Stereo Audio Jack
- Small gauge Stereo Audio wire
- 1Kohm Thumbwheel Audio Potentiometer for Volume Control
- Heat Shrink Tubing
- Solder
- Solder Sucker or Braid (in case of emergency)

Tools you will need:

- Hot Glue Gun
- Soldering Iron
- Wirestrippers
- Heat Gun (optional - you can use a soldering iron to carefully melt heat shrink)
-Digital Multimeter to test connections (may only need it if you have issues)

Step 2: Secret Places to Get the Parts You Need!

To find the parts you need you may not need to look any further than from your junk electronics pile or an old PC. If you can't find anything there you could ask a neighbor or friend if you can raid their pile or they may even have may have some parts just kicking around. The following is a list of specific places you might look for the parts you need:

3.5mm Female Stereo Audio Jack

- Discman
- Walkman
- Stereo or Boombox
- PC Modem board
- PC sound card
- PC CD/DVD drive
- Portable Radios
- Motherboards
- Automobile Head unit

3.5mm Male Stereo Audio Jack

- Headphones
- Earbuds
- 3.5mm Stereo extension cable

1Kohm Thumbwheel Audio Potentiometer

- Pair of old headphones with a volume control potentiometer (if you can't find an old pair you can always buy some cheap ones on ebay for $2-3)
- Mouser (this style will only work for one channel so you will need 2)
- Digikey (not sure if this one is logarithmic or not)
- If you find any other places to find these please let me know because my resources are tapped

I learned a very valuable lesson while testing salvaged thumbwheels out of old electronics -> these thumbwheels control the gain of amplifier chips and are not suitable for direct (in-line) volume control. The thumbwheels I salvaged from CD drives were 50Kohm and the ones I salvaged from Discmans were 10Kohm. The value needed for this project is only 1Kohm and as it turns out they are much harder to find then I thought.

If you cannot possibily find the other parts anywhere for this particular project, then as a last resort you could always go to your neighborhood Radio Shack (The Source by CC in Canada) or order online surplus parts from places like Electronic Goldmine .

Step 3: Shortcut Already?

SHORTCUT!

Here's some advice that ended up saving me tons of time and it probably will for you as well if you can find an old set of Headphones with built-in volume adjust. So take your old headphones (mine had a loose speaker connection) or a pair that are just a faux pas in today's fashion world and rob the volume adjust from them. Cut the connection as close to the speakers as possible to keep the length of your project as long as can be. Then strip back the rubbery insulation to expose the audio channel wires as well as the, usually copper, ground sheath. Now skip ahead to Step 5!

Diagram Abreviations:

CHL - Left Audio Channel
CHR - Right Audio Channel
GND - Copper sheath around both channel wires which makes the Ground connection

Step 4: Thumb Wheel Method

So if you simply cannot find a set of headphones with volume control to salvage all is not lost, there is always the Thumb Wheel Method!

Friendly Reminder: Place those Safety Glasses on before you start soldering to save your eyes from potential magma hot, rouge solder splashes.

Find a Male 3.5mm audio plug with some wire left on it, cut the wire where you'd like the pot to go. Now grab your Thumb wheel and solder all the Ground sheaths together and then onto the left most pin (Pin 1). Next solder the the Channel (CH) wires from the male jack to Pin 2 for CHR & Pin 3 for CHL, then the output wires going to the female jack will be respectively soldered to Pin 4 for CHL & Pin 5 for CHR.

If you're curious about the Thumb Wheel Pin-out, here's what I found online: With the Thumb wheel facing up and the 5-pin edge facing toward you. From left to right, the pins are:

1) Common (GND for audio use)
2) R1 Wiper (Out 1 for audio)
3) R2 Wiper (Out 2 for audio)
4) R2 End (In 2 for audio)
5) R1 End (In 1 for audio)

Now would be a good time to measure to use you Digital Multimeter on the Ohm setting the potentiometer values, a value range of around 0-1Kohm for each channel is what we are looking for.

NOTE: In my diagram I have the inputs and outputs swapped but since the Potentiometer is being used in a variable resistor configuration it doesn't matter if they are swapped. (It was easier for me to draw the diagram that way :D )

Solder on your male stereo jack and extra bit of audio cable to the pot (as seen in the 5th picture) and you should be on your way to the next step.

Step 5: Attach the Final Connector

Now Solder from the output side of the Volume Control Pot to the Female 3.5mm jack.

Remember:

CHL connection corresponds to the tip
CHR connection to the Middle band
GND connection to the Largest band.

A little food for thought about Audio potentiometers; they are actually not Linear in operation but Logarithmic. Our brains actually interpret sound Logarithmically (that's why hearing tests are measured in Decibels) so the resistance of the volume control must be adjusted Logarithmically in order for the variance in volume to sound smooth to our ears.

Step 6: STOP.....Give It a Test

STOP....don't proceed any further until you Test er' Out. You don't want to make any permanent/semi-permanent adjustments to you project until you know it's working just in case there might be a loose or broken connection somewhere, or you've wired up you channels on the wrong pins of a connector....I'm speaking from experience here, these things happen :).

Grab your favorite music player and see if those tunes will indeed make you bounce.

Some possible Issues you may face:

- Your music player of choice is not working, try another
- You've accidentally swapped the order of CHL & CHR on the inputs or outputs
- A solder joint has come loose somewhere
- One of the audio jacks you've used is too long or too short to make the proper connections, try pushing/pulling your connections a bit in fine increments
- You may have a Thumbwheel that is too high in resistance or is bad

Do not proceed to the next step until all is good, you may need an Ohmmeter to help you out.

Step 7: Ok You're Good, Put Some Final Touches on It

Now that everything is working add some hot glue on the connections of the Female connector to protect the wiring and solder-joints from being damaged. Then take out some of your favorite colored heatshrink tubing and seal up the business end of your project.