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View Full Version : Headunit voltage preouts



wong05tsx
02-11-2008, 03:42 AM
Quoted directly from a PM me and this guy on the acura boards that is making me a custom made balun [converts stock HU's balanced differential inputs into unbalanced, in a nutshell]. I've read on this board that higher preouts voltage can result in slightly better SQ.
Here's what he says:



I was able to finish you unit last night after work. I want to make a few measurements on the one installed in my TSX before I ship yours. I also want to ďburnĒ your unit in on the bench today to weed out any potential component problems. I should be able to ship Monday.

Now, about the pre amp voltage, Sound quality and preamp voltage are not directly related. In fact, when it comes to sound quality pre amp voltage doesnít factor in at all. Your friendís new deck sounded better for a number of reasons and pre amp voltage was not one of them. If I connected my hi end 20 bit home audio file deck to your friends amp it would blow you away and it only has a 1 volt pre out.

Aftermarket deck manufactures raised output voltage to overcome noise pick up on the audio patch cables between the HU and amp, thatís it, that is the only reason they did it. The reason for it is to reduce the amount of noisy installation complaints. It has no positive effect on sound quality if a signal in amplified to 1 volt or 10 volts. It can have a negative impact on noise generated in the power amps input stage and it will increase THD and IM.

I can write a book on the negative effects of high pre amp voltages as well as how you can not do proper A/B tests in a car environment.

The pre amp level on the factory HU is 4 v at 0dB, but since the signal is differential you get 8 volts in terms signal to noise on the cable and even more then that when you feed it through a differential amp. In other words, to get the same noise pick up reduction on the interconnect cables you would need an aftermarket HU with 8v pre outs. Even then, you still would not get the same S/N ration because of the added CMRR of the diff amp.

jeff


/discuss

Fiercetimbo17
02-11-2008, 04:21 AM
what he is basically saying is that higher preout voltage just means less chance of noise, what incorrect about that statement? Just becuase you have 8v preouts doesnt mean that unit is better than something with 2v your just less likely to pic up noise