I play an electric grand piano in a restaurant and the owner asked me to put the piano through the house system so they can hear the music all over the restaurant. The piano has two [stereo] RCA jacks [outs] and the other end [a preamp connected to an amp] also has 2 [stereo] RCA jacks [in]. The distance between the piano and the house system is about 75 feet. Can someone help me to figure out the best [and cheapest ] way to do this? Can I go that far without boosting the signal? What type of wire? Should I use 2 coax cables? Thanks! John .

 

Of course you need to use shielded audio cable (coax). If you don't then the wires will pickup 50Hz or 60Hz mains hum.

If the output impedance of the piano is not very low (it probably isn't) then the capacitance of the long cable will cut high frequencies.

 

I play an electric grand piano in a restaurant and the owner asked me to put the piano through the house system so they can hear the music all over the restaurant. The piano has two [stereo] RCA jacks [outs] and the other end [a preamp connected to an amp] also has 2 [stereo] RCA jacks [in]. The distance between the piano and the house system is about 75 feet. .

That is likely what's called a line level output which typically has an output impedance in the 500 - 1K Ohm range and is not a low source impedance. As said above, a long coax line will trim the high frequencies a bit as it has a certain amount of capacitance per foot so it looks like a capacitor across the output impedance.

Good audio cables have about 20 - 30pF of capacitance per foot, so it might be 2200pF for 75 feet. If that's in parallel with 1k Ohm, that puts a corner frequency at about 70 kHz if I did the math right. I don't think it will hurt you too much. Your other option could be to use RG-6 video cable as it is very low loss at high frequency.

 

The best way to distribute audio to a distant point is to transmit them at speaker level.
In hotel audio distribution , the audio is amplified and the output is fed through a transformer. The out put level is increased to about 50 to 100 Volts depending on the distance to be distributed.
The transformer impedance is matched to the amount of tapping or hotel rooms that the audio is distributed to.
This is how we distribute a common audio to all the rooms in a typical hotel.

But in your case, if you want a low level signal to be fed into a sound input at a considerable distance, I advice you to use instrumentation cable to feed the audio and to use balanced preamp at the input of the sound system and at the out put of the piano.
Balanced line driving eliminates hums and noise picked up during low level, long distance audio feeding.
All depends on the quality of the balanced line driver and receiver and the quality of the audio cable used to transmit the Signal

Rifaa