Step 1: Collect Your Staff
1. Audio Compact Cassette adapter [cost about 1 USD]
2. A2DP Bluetooth receiver with battery [ cost about 10 USD] finally I take this one from Ebay (print screen from ebay in attached pdf if link is broken or item is moved to archive)
What is important !!!
We can't use components from standard handsfree. Most of them did not have A2DP bluetooth profile, and our phones recognize them as a handsfree not speakers system. In case of android phones there is a solution Btmono app, in case of iphone only for jaliebroken phones.
Step 2: Take Out the Cover and Cut Jack Wire
2. Cut also jack from cassette
Step 3: Solder Wires and Secure
Yous can also remove speaker and put wire inside with small knot to secure connection :)
Step 4: The End !
Good luck !