Everything for Electronics

Tech Forum

2022 Issue-1

Adding Aux Input To Stereo

My car stereo boasts an AM/FM radio and a cassette player (2007 model. My smartphone, however, has all my stored music, Pandora, Amazon music, and even Satellite radio. There is no auxilliary jack or Bluetooth to connect my phone to the car stereo like with new units.

Is there a way to tap into the cassette deck circuitry and add an aux jack to use my phone as an audio source? Would I need a preamp or other circuit to create an interface or just a direct connection at some point inside the stereo?

Gilberto Onio
Framingham, MA

Associated files:


Before you get out your tools and start digging around your cassette player, the good news is there is an easier way! It’s lucky that you are interested in connecting an audio source to a cassette player rather than to a CD player! Years ago, in the heyday of cassette systems, a ‘cassette adapter’ was widely available. This was simply a cassette shell with a magnetic head inside, just like a player’s tape head. This adapter was inserted into the player, like any cassette, and its cable was plugged into the stereo output of whatever you desired. The head in the adapter magnetically coupled the audio to the player’s head and in most cases, it played quite well.

The better news is they are still available, Amazon, eBay, Walmart and many others still list them at around $5 plus any shipping. Maybe, if you have a junker cassette unit or parts, you may be able to DIY an adapter but I don’t know if the cassette player head impedance is different in the adapters,or if that would make any difference. I don’t think this concept presents any harm to the cassette player.

But, is it all really worth the effort to save $5?

Len Powell
Finksburg, MD

My 2002 Subaru doesn't have any "modern" connections either. The simple solution was an Ion Audio Cassette Adapter. It's basically a cassette tape case with the electronics for a Bluetooth connection inside. A short, flexible wire sticks out of the player for the antenna. This particular brand seems to no longer be available from Amazon, but search "bluetooth audio cassette adapter" for other options.

Rick Gregory
Salt Lake City, Utah

There are two was to do this easily, without doing any mods to the circuit.

  1. Buy an FM radio transmitter that plugs into your device & then transmits to the FM radio in your car. There are many different ones to choose from on Amazon & eBay; search on, "Bluetooth FM Transmitter for car" will only show the Bluetooth devices or "3.5 mm Stereo jack to FM transmitter" which will also find devices that plug into your phone/mp3 player with a 3.5mm stereo plug. It even found a Bluetooth transmitter!
  2. Buy a cassette that plugs into your device and send the audio to a magnetic head in the cassette that then passes that audio onto the magnetic head in the cassette player in the car. see: Arsvita-Audio-Cassette-Adapter-Auxillary/ at: https://www.amazon.com/dp/B07N2KPTGW
  3. Last, if you really want to take the radio/cassette player out and dig into it you probably can add a stereo port. The easiest way would be to find the stereo volume controls and add your input just before or after the volume control. NOTE: If you add the port just after the volume control you will have to change the volume with your device. If you add your input before the volume control then you'll be able to adjust the volume with your radio's volume control and with your device.

Phil Karras
Mount Airy, MD

Kurt Stefans
Valparaiso, IN

When I bought my first XM Radio in 2004, It came with a "cassette adaptor". It looks like a cassette tape with a cable and stereo plug (like the kind on your headphones). I never used it, so I don't know how effective it was. You might be able to find one on line. Most cars today don't come with cassette players so there may be a surplus of these out there.

Rick Drapala
Yuma, AZ