Car tapedeck to bluetooth noise

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mb82

219 posts

Master Geek

#246693 17-Feb-2019 17:52

I have gutted the tape mechanism out of my car radio and installed a stepdown voltage board and bluetooth module from ali express. It is powered from the wires which use to run the cassette motor. The audio wires (left right & ground) run from the bluetooth module to the pre amplifier for the old tapedeck. Works well apart from I have interferance at high volume see video:

https://www.youtube.com/watch?v=J8sTvYBkb8w&feature=youtu.be

Any ideas how to get rid of interference? I used some standard thin wire to connect the bluetooth module to the preamp I am wondering if it needs to be shielded or something? The ground wire goes from the ground marked on the bluetooth module to the ground of the preamp. Or maybe the noise is coming from the powersupply for the old tape unit or the stepdown/bluetooth board itself? Any ideas?

frankv

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#2181957 18-Feb-2019 12:03

What are you using to step-down the voltage? The cheap buck converters produce lots of noise.

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hsvhel

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#2181958 18-Feb-2019 12:05

Can you not change the head unit for a newer one with bluetooth?

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mb82

219 posts

Master Geek

#2183242 18-Feb-2019 20:52

frankv:

What are you using to step-down the voltage? The cheap buck converters produce lots of noise.

Yes I have a cheap buck converter.

hsvhel:

Can you not change the head unit for a newer one with bluetooth?

I could but flashy new radios look out of place in older cars I also don't want a theft magnet.

Goosey

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#2183279 18-Feb-2019 21:10

cool.

if all else fails...then check out....

https://www.trademe.co.nz/services/trades/automotive/auction-1202475345.htm

https://www.soundlabsgroup.com.au/c/Classic-Retro-Car-Audio/Classic+and+Retro+Car+Audio.html

https://www.retromanufacturing.com/pages/radios

http://www.phoenixaudionz.com/convert.html

TBH, most crooks dont tend to steal car radios these days... (and theres more value in ipods,phones,cameras,ipads) !

Goosey

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#2183281 18-Feb-2019 21:12

sounds like definitely the DC noise from the tape deck. Something needs to be grounded better?

richms

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#2183328 18-Feb-2019 23:34

Probably have a groundloop, or the input amp for the tape head is not expecting a signal with reference to 0v, but is using the head as a ballanced input so you are saturating it by driving it to 0v.

I would suggest sticking a pair of audio transformers between the output of the board and the input if you are going to go thru the amplifier.

The other option is to go straight to the volume potentiometer, as old audio circuits would just run the audio signal straight thru the potentiometer, using a 2 channel one, one channel for each of the stereo channels - bypassing the amplifier and selectors and stuff entirely. That would lose the FM radio if you still bother with that however.

Richard rich.ms