Help with amp input sensitivity.

[valkodav]

Hello,

I am meeting some difficulties in understanding the relation between input sensitivity, gain, output voltage.

I have a source rated at 2V output voltage, an amp with input sensitivity of 1.25V (8volts maximum) and gain of 29dB.

Im thinking of buying preamp with output voltage of 1V, 16dB gain ( the input sensitivity is not stated).

I don't know if it will be a good match between all in the chain. To be more precise i understand it to some degree.

A guy in other forum did some calculations for me and told me i need 4.77RMS output from the preamp to the amp to drive it, won't that overdrive the amp circuits?. How is this going to happen when the input sensitivity of the amp is expectign a signal of 1.25V ?

When the 2V from the CD get in the preamp its getting attenuated ( to what extend?), then is it amplified by the preamp by its gain or no ? should the signal be amplified to the output voltage of 1V or more ?

The more articles i read on input sensitivity, gain and so on the more confused i am.

I would very much appreciate it if i get it clear. Thanks.

 

[Vladimir]

If your preamplifier input sensitivity is 500mV, it means it will need 500mV signal in its inputs from a source to reach maximum output, which lets say is 1V. That particular preamp needs 500mV input to create 1V output. If you give it half, it will output half.

Next in the chain is the power amp. If its input sensitivity is 1.25V, it means it needs 1.25V to reach 100% of its output in W to the speakers. If you feed it 1V from the preamp, it wont go 100% of its capacity but 80% at best. If you feed it 1.5V, it will go to overload and clipping (above 1%THD).

Now let's get back to the preamp and source. Your typical digital source will output around 2V max. If you feed it to a 500mV input sensitivity preamp, it will go loud to it's maximum output of 1V with just 500mV. Which means you can only turn the volume knob one quarter away (500mV of 2V is 25%) without creating overload and clipping. That is your usable volume control area, up to 10-11 o'clock at best.

If your preamp has input sensitivity of 2V, you can turn the volume knob all the way to get the 1V output, which sent to the power amp will create 80% output.

I hope this helps understanding gain staging a bit.