I played around making my own from eBay componants.
It worked and I added a Bluetooth input device so it was wireless to my phone.
But the cobbled together ebay componants we're sketchy at best.
I haven't followed up yet but my ultimate goal was to make a stand alone box battery or cig lighter powered and completely wireless to allow Bluetooth input and am radio output.
As mentioned above it requires the AM radio to function and mine recently degraded so I just listen to my phone with headphones, now.