Originally Posted by alaxfire

I am no electronics expert, but I do know that wiring to the amp inputs with a signal of less than 3-4 volts peak to peak will not give good results. That is why when putting in aftermarket head units, if the pre-amp outputs are listed as 2 volts, you will have to use the speaker wires to drive the amp.
I have tried the following in my Roadster :

Sony CDXGT54UIW_EN_FR_ES - pre-amps are 4v, works fine. ( traded to maxcichon )
Alpine IDA-X001 - pre-amps too low, have to use the speaker wires. ( currently installed )
Blaupuncht Melborne SD27 - plug and play ( still have it )
OEM unit - works fine ( still have it )

Anyone ever measure the p-p of the earphone signal from a smartphone ?