Holy Flying Crap! A Passive iPod Preamplifier

Tired of hooking your iPod up to your car or stereo and hearing low-level lackluster sound? Here's a way to turn ten dollars or so in parts into an iPod preamplifier that uses no external power.

If you had the minerals to sit through my ponderously long article about the failure endemic in using your headphone jack to hook your iPod (or similar portable media player) to your stereo, and are comfortable with run-on sentences filled with total win, then read on.

Let me pedantically re-state the problem:  the headphone jack of your iPod is not ideal for connecting to your stereo, whether its in your home, office, or car. The headphone jack is great for headphones, but really sub-par for connecting to a stereo. There are two problems:


Boost your ipod/portable media player output with zero external power
A simple (yet awesome) little box that sits between your iPod and your stereo
This is a great little preamp for your car--no need to power it.
  1. The impedance mismatch that makes your tunes sound mushy.
  2. A lack of output voltage means that you have to crank up your stereo volume to get a decent listening level. (And the corresponding heart-attack when you switch your amp from iPod to radio or CD and the volume is through the roof.)

There's this Fellow Named PRR

Being the well-adjusted successful guy that I am, I like to spend endless hours cruising the internet reading forums, articles and just about anything related to audio electronics. While digging through iPod to Line-In mismatches, I happened across this wonderful thread. A fellow name PRR posted a few solutions, one of which was a passive, transformer-based circuit that purported to boost low-voltage output devices such as an iPod.

I was transfixed; here was a passive (no external power required!) solution that seemed to good to be true. And as it happened, I had a few of the specified Radio Shack transformers in stock! After a bit of diddling around, I had the thing hooked up. I connected it to my A/B comparison box and booted up the iPod, cued up Thomas Dolby's The Flat Earth, and started the big comparo.

Passive iPod Preamplifier Test Rig

Using my small test rig for transformer hookup

Radio Shack Audio Transformer, Catalog # 273-1380The end result? A great sounding boost. Not earth-shattering volume as would be realized in an active (opamp or transistor) circuit, but all of the mush was gone. Bass and treble were both significantly enhanced, and the sound improvement was pretty dramatic for a passive circuit.

So Let's Build One!

This device is really simply, basically four parts. Here's what you'll need:

  1. a pair of Radio Shack Audio Transformers (Catalog #273-1380)
  2. a pair of 3.5mm stereo input jacks
  3. (Optional but recommended) a fun enclosure to hold the parts together.
  4. (Optional but recommended) a soldering iron, some heat shrink tubing, a quart of cheap Chianti, and one of those cool bendy-straws.

Here's the schematic:

Passive iPod Preamplifier Schematic

Because the transformers are small, you can choose from a wide range of enclosures. I used Radio Shack's 3" x 2" x 1" enclosure, catalog # 270-1801.

Radio Shack Project Enclosure Catalog # 270-1801

Radio Shack Project Enclosure

DIY Passive iPod Preamplifier

All wired up

DIY Passive iPod Preamplifier

Ready for the car!

A Couple of Final Notes

  • Be sure to plug this in the right way--if you get the inputs and outputs reverse, the sound will actually be worse, not better :) When you build your box, use a sharpie or some other clever labeling mechanism to denote Input and Output.
  • This works with the line out signal from an iPod also.

(c) 2009-2012. This work is licensed under a Creative Commons License