Making own stereo, need help getting 500mv to 5v amp (guessing)

[jpwhre]

This is my first post.  Flame on if need.

I'm thinking of getting something like this

https://www.youtube.com/watch?v=NtdvN0UFO2Y

or seen here

https://www.amazon.com/s?k=bluetooth+fm+mps+decoder+board&ref=nb_sb_noss

as well as getting one of these

https://www.amazon.com/Decoders-7-1-Channel-Decoder-Board-Single-Supply/dp/B079KF9749/ref=pd_ybh_a_3?_encoding=UTF8&psc=1&refRID=MW8XE7MNRKACRM774MGN

Found this looking at one on ebay for instructions. The "AUX L" mark in the signal input part of the decoder board is the analog left channel audio input, the "AUX R" mark is the analog right channel audio input.

The first item i have linked, according to the video, only puts out 465 (ish) milivolts turned all the way up and i can only assume the 7.1 decoder input is 5v

My plan is to remove the factory stereo and put a 7 inch tablet in place, remove bin and put in some plastic, move the A/C controls to the new plastic in bin and add the FM Bluetooth....... decoder in with it, and put the 7.1 decoder where the A/C controls used to be.

But I need to get 500mv output to 5v and don't know how.

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