Acceptable voltage ranges for pre-amp outs

[Denis29]

I am purchasing an Audiosource AMP100, which seems to be a fine amp for those on tight budget, and one of its specs is that input sensitivity is "900mV input for rated 50W output into 8 ohms". This made me curious about two things:

1) what does input sensitivity mean? is it what pre-out voltage gets attenuated to by the amp in order to reach peak power?

1) on receivers that need external amp(s), what range of voltages is common to pre-amp ports? Say, between 1--5V? 0.5--4V? I realize all devices are different: I'm just looking for a ballpark figure.

Sorry for n00b questions and thanks in advance.

 

[highfigh]

I am purchasing an Audiosource AMP100, which seems to be a fine amp for those on tight budget, and one of its specs is that input sensitivity is "900mV input for rated 50W output into 8 ohms". This made me curious about two things:

1) what does input sensitivity mean? is it what pre-out voltage gets attenuated to by the amp in order to reach peak power?

1) on receivers that need external amp(s), what range of voltages is common to pre-amp ports? Say, between 1--5V? 0.5--4V? I realize all devices are different: I'm just looking for a ballpark figure.

Sorry for n00b questions and thanks in advance.

Amplifiers develop the output power based on a designed-in voltage differential, meaning that for every increment of voltage, the amp will provide a certain amount of voltage gain. If the differential is 20:1, for every increment of voltage at the input, the output will be 20 times that. Input sensitivity of .9V is compatible with a lot of equipment. Pro audio is usually switchable for -10/+4 at the input and the difference has to do with which input is used- high impedance or low. Volume increases and decreases aren't linear- the range of the softest to loudest sounds we can perceive is subject to the ambient noise level (noise floor, if you want to call it that) and because it's almost impossible to have a totally quiet space, any room noise will conceal some of the noise produced by the equipment.

The preamp's signal is attenuated before it goes to the power amp because with gain, comes noise. They use intermediate gain stages between the source's input and the preamp's output that isn't as drastic as the power amplifier's gain so it doesn't introduce noise, with the phono section being the main exception to this and you'll notice that the phono section is always the one with the most noise because it provides the most gain.

 

[Josuah]

If your amp input sensitivity is 0.9V then it'll be putting out it's max power when the input signal is 0.9V. It's probably Vrms (averaged voltage) rather than Vpeak.

A consumer pre-amp is likely to output somewhere between 0Vrms (silent) to a few volts. In other words, you won't set your pre-amp to maximum volume.

 

[Denis29]

Thank you for those replies - very helpful.

If I am understanding correctly... To reduce the gain that an amplifier needs to produce, to reduce noise, is it better then to have the pre-outs set to, say, 4V RMS output instead of, say, 2V RMS?

 

[Josuah]

Well, an amplifier usually has a fixed gain. Which also means a fixed noise floor. You hook up the amplifier to your speakers, and depending on your speaker sensitivity and the noise floor of your amp, you either hear something or you don't.

Likewise, your pre-amp has a noise floor. Some of the noise may occur before the "volume stage". So when you turn up the volume, you turn up the noise as well. Some of the noise may occur after the "volume stage" and so turning up the volume doesn't change anything.

If you have a pre-amp with audible noise before the "volume stage" then a lower volume setting on your pre-amp would be good. In which case you may want the signal going into your pre-amp (i.e. from your DAC or CD player) to have a higher voltage if you like to listen loud.

In my experience, typical single-ended RCA voltage from a CD player is around 2 Vpeak. Still, usually people end up sending less than a volt into their amp because that's often plenty loud enough already. In other words, picking a higher voltage level isn't likely to be necessary.

Of course, just like for the pre-amp, your CD player or DAC will have a noise floor. But you have no control over that, other than getting a different source. Same as with the amp; if the amp noise floor is too high for you then you need to get a new amp. If the advertised specifications are reliable, then you want to look at the signal-to-noise ratio.