Am looking at a new head unit. Narrowed choice to jvc kd-sx985 and kd-LH2000. Seems to me the 985's only differences is a motorised face and 4 volt preouts but is an older model range. I can get the Lh2000 for $150NZ cheaper. What do the experts think? Does the 4 volt vs 2 volt make much difference. Also what sort of connection goes between the telephone mute and my nokia car kit?

(I've just assumed that you're talking about subs and that's all that I have experience of when it comes to different voltages).

An amplifier has to take a small input signal from the stereo and <u>amplify</u> it into a big output signal to run the speakers. So, if it starts with a bigger signal, then it can:
a) give you an even stronger output signal (more volume / punch / rumble) into your speakers
or b) be turned down a bit so that it doesn't have to work so hard to give you the same output.

I'm not an expert on amps but these are the results I found a few years ago when my 2v stereo signal was feeding a cheap amp that was running a couple of 12" subs. When I fed the stereo into an active crossover with variable signal boost, I was then able to feed a punchier signal into the subs and the difference was significant. Incidentally, I wouldn't recommend a cheap active crossover in conjunction with an amp that's running full-range speakers - you lose quite a bit of clarity and end up wih a 'loud but cheap' sound.

The difference between 4v and 2v should be feck all in theory. A 4v signal will be less susceptible to noise, as the signal is at a much higher level relatively than the noise.

All amps have a gain control which is a little like a volume control. To produce maximum output from the amp, you need to set the gain control appropriately. Whether the input signal is 2V or 4V should not matter one bit - for 2v, the gain setting will be higher than for 4v. As the gain stage takes naff all power to drive, this will not effect the amp's output/efficiency/...

Saying that, someone has claimed a dB increase when competing in SPL by upping input voltage, but that could be for a variety of reasons not necessarily down to gain.

Cheers,

Nick.

cheers guys. dont think i will worry bout the voltage issue when making my choice. Any ideas about the hookup between carkit and telphone mute input?

Oh (embarrassed face). If Chiark is a moderator, I guess he knows this stuff more than me. Sorry if I was talking complete rubbish - I was talking from experience .... but it was a long time ago. Maybe I should stop buying such cheap amps !

no need to apologise, it's just as likely that I'm wrong :D - "moderator" doesn't mean I have a clue what I'm talking about :)

Theory is that it shouldn't made a difference other than to lower the noise floor of a system, but someone has found an improvement in SPL when competing... But this could be for a variety of reasons and shouldn't be to do with gains...