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I have a old autoradio (cassette and not AUX input ) in my car. But i don't want change because it pretty. I just want to add bluetooth. I leave fm receiver side for the true audio / radio.

I want to know if i purchase both parts :

I connect the audio amplifier with bluetooh receiver and power amplifier with speaker and i add a switch, to switch(speakers) between true audioradio/power amplifier.

I know i must add a power convert 12V->5V for the Bluetooth module.

I want to know if this is good "cheap" solution ?

Sorry for my English, I'm French.

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  • \$\begingroup\$ A simple way, if you don't need cassettes anymore, would be to inject the bluetooth audio inside the existing autoradio (at the output of the tape preamplifier), and wiring some switches to make the autoradio think a cassette is inserted. This way you keep the previous amplifier and wiring. \$\endgroup\$ – Aleix Mercader Mar 17 '16 at 11:43
  • \$\begingroup\$ Thanks for your reply. I thought too for this solution is true that is the cheapest solution and the more clever. But it's more complicated. My knowledges in electronic is not enough to do that. I already seen a post who someone do that. If i brake the auto radio will be more expensive that buy amp/bluetooth \$\endgroup\$ – kiki67100 Mar 18 '16 at 17:09
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Yes, that would work. You need a good heatsink for the amplifier chip and you need heatsink paste to get good heat transfer between the chip and the heatsink.

TDA chip

Figure 1. TDA7388 chip. Note that eight wires need to be switched. None of the speakers is connected to GND (battery '-').

The big problem with this is that you have to switch eight wires from the radio to the speakers. This will give you many hours work lying upside-down in your car with your head under the dashboard.

FM transmitter, 3.5mm

Figure 2. FM transmitter.

If your FM radio is good then a much simpler solution is to use a mini 3.5mm FM transmitter.

  • Plug transmitter into music player.
  • Find a position on the FM band where there is no local station.
  • Tune the transmitter to that station.

Your pretty car radio antenna will pick up the signal and you have no other work to do!

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 3. Bluetooth and FM.

If you really want no wires from your music player then you could go Bluetooth -> FM as shown in Figure 3. It should work but maybe the audio quality will get a little bit worse.

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  • \$\begingroup\$ Thanks for your reply. Yes I know for the figure 1 it will hurt my neck ;-) I didn't think about the heat, thanks for your precision, I thought to add the audio amplifier and bluetooth receiver a box, maybe with a little fan. I think is more easy to unplug the speaker from the true autoradio and use a old phone as "smart auto radio". for the figure 2 i currently use this but the sound quality is poor and a lot of parasite, and i can't take i call. But i don't want to use fm bluetooth receiver to take call because anyone listen the frequency can listen my call... \$\endgroup\$ – kiki67100 Mar 17 '16 at 9:12
  • \$\begingroup\$ Even with a fan you will need a heatsink but maybe not so large. I forgot that the phone will use audio out for phone calls! \$\endgroup\$ – Transistor Mar 17 '16 at 9:28

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