[Gary Albach]

In a post in the Show and Tell forum, I mentioned that I had added an MP3/Bluetooth input to my Addison 5A. I used the circuit in the attached schematic and housed it in a small plastic projects box. The box is mounted on the inside wall of the cabinet, using Velcro tape so that it can be easily removed. The output jack from the box mates with a 3.5mm stereo plug and shielded cable with both channels in parallel, which in turn is connected across the volume control of the radio. The capacitor in the circuit provides isolation from DC voltages in the radio. The transformer provides safety isolation between the radio and the MP3 source, and approximately matches the low output impedance of the MP3 device to the high input impedance of the radio. Any output transformer will work. The resistors in the input to the circuit form a simple mixer of the two stereo channels.

For wired operation, I use a cable with two male plugs between the MP3 player (usually the headphone jack on my iPod) and the radio. For Bluetooth operation from my cell phone I use a cheap Bluetooth receiver plugged into the MP3 input, as shown in the attached picture. I buy them from AliExpress:
https://www.aliexpress.com/item/4000093932866.html?spm=a2g0s.9042311.0.0.625c4c4dHxO9MX

Gary

Attachments:

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   MP3-input-schematic.jpg
   

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   MP3-circuit-s.jpg
   

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   MP3-input-s.jpg
   

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   MP3-Bluetooth-s..jpg
   

[Gerry O’Hara]

Hi Gary,
How did you power the Bluetoooth adapter? – just a small USB wall charger or from the radio somehow?

Gerry

[Gary Albach]

I power the Bluetooth receiver/adapter from a USB wall charger.

Am currently playing around with a DROC CA200367 Bluetooth car radio adapter sold on Amazon here:
https://www.amazon.ca/gp/product/B07KXG3NG4/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
It has two advantages: first, it can run on 5 – 35 volts, allowing a wide range of ‘wall warts’ to power it, and second, it connects automatically with a Bluetooth transmitter, without having to push any buttons. Unfortunately, it draws about 45 mA and so I’ve not been able to find a place within an AA5 to ‘steal’ this much DC low-voltage power.

Rick Williams in Edmonton has pointed me to an even more sophisticated FM/Bluetooth adapter for car radios, described here:
http://www.tech-retro.com/Aurora_Design/BT.html
Thanks, Rick.

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