Adding bluetooth input to old stereo

Question

I am adding a bluetooth receiver to an old suitcase style record player / am radio.

I have a bluetooth receiver which runs of 5v (usb normally). I have connected this to the volume pot, through the radio/gram switch, so that the bluetooth is only connected in gram mode (when it's silent with no record playing).

This works fine. The only issue is that the volume is quite loud, even when the volume knob on the stereo is at it's lowest setting. I tried to fix this, by putting in a 500ohm-10k resistor on the common connection of the audio cable, however as soon as I did this, I can hear radio interference on the stereo in gram mode and some ticking (a bit faster than 1 per second).

I hear the same interference when the common connection is disconnected!

Any ideas how I can get the volume down without introducing this interference sound?

Answer 1

If you're adding a resistor in series, then you're just limiting the current. To lower the output (sound) amplitude, you need to lower the amplitude of the voltage signal feeding the speakers. Thus, you want a voltage divider. If you have not already, I would try using a pot as a voltage divider and seeing what resistance values work the best for you.