help designing RC level isolation transformer

[muddasirwaheedmalik]

hi everyone , i have an old school pioneer car amplifier. gm 4200... a superb amplifer.... its RCA input buffer/noise eliminator is fried....however DIN input is working but DIN input is giving huge noise when connected with RCA connection with a latest sony head unit......i tried my luck with a speaker level to rca level convertor and the noise was gone..... but i did not want to use the distorted output of the high level speaker output of the head unit...
so i pulled open the converter which is basically an isolation transformer with a voltage divider network....a 100 ohm resistor with 4.7 ohm in series and the inputs of the transformer are connected at 4.7 ohm resistor......the transformer i tested is 1:4 step up transformer.


now i cannot use the same ciructput with rca level output as it has very low impedance input .....amplifier ususally haave 10k + input impedance............please advice how to go about it.

[muddasirwaheedmalik]

with 43k parallel to tranformer input on a voltage divider network of 430 ohm+43k ohm the bass rolllllssss off...... very low impedance of tranformer at low frequencies means a very small impedance in parallel with 43 kohm...... means a net low resistance and therefore very small voltage output...???? what to do?