Question about preamp input sensitivity/output level

[QMuse]

So, here is what it says in the specs of my Rotel preamp:

Input Sensitivity/Impedance
Line Level: 200 mV/47 kohms

Preamp Output Level
1.2 V (200 mV Input)

This is from the schematics, op amps are NJM5532:

Can somebody pls explain how does this actually work assuming volume is set to 100% in all cases:

- do I get 1.2V at the output only when 200mV is applied to the input?
- what output level do I get when a CD player with output level of 2V is connected to the line input of this preamp? Is it also 1.2V?
- what output level do I get with (for example) 0.7V? Also 1.2V?

 

[SIY]

So, here is what it says in the specs of my Rotel preamp:

Input Sensitivity/Impedance
Line Level: 200 mV/47 kohms

Preamp Output Level
1.2 V (200 mV Input)

This is from the schematics, op amps are NJM5532:

View attachment 51121

Can somebody pls explain how does this actually work assuming volume is set to 100% in all cases:

- do I get 1.2V at the output only when 200mV is applied to the input?
- what output level do I get when a CD player with output level of 2V is connected to the line input of this preamp? Is it also 1.2V?
- what output level do I get with (for example) 0.7V? Also 1.2V?

What you have there is a poorly written spec. I won't pick on Rotel, since they make generally good gear and bad spec writing is fairly universal...

In any case, if I read your block diagram correctly, the line amp gain is 16 dB, or about 6.3 V/V. So with the volume control cranked to full, 200mV input gives you an output of 0.2x6.3 = 1.26V. With a 2V input and the volume cranked to full, you have an output of 2x6.3 = 12.6V. Now, it's not evident if the preamp is capable of that much output, and it's likely to be clipping. But that's why God invented the volume control- if you actually had 12.6V out, 99% of power amps would be in gross clipping anyway, so if the volume control is lowered, you'll have a clean output and the capability of driving ordinary power amps to their maximum capability.

 

[QMuse]

What you have there is a poorly written spec. I won't pick on Rotel, since they make generally good gear and bad spec writing is fairly universal...

In any case, if I read your block diagram correctly, the line amp gain is 16 dB, or about 6.3 V/V. So with the volume control cranked to full, 200mV input gives you an output of 0.2x6.3 = 1.26V. With a 2V input and the volume cranked to full, you have an output of 2x6.3 = 12.6V. Now, it's not evident if the preamp is capable of that much output, and it's likely to be clipping. But that's why God invented the volume control- if you actually had 12.6V out, 99% of power amps would be in gross clipping anyway, so if the volume control is lowered, you'll have a clean output and the capability of driving ordinary power amps to their maximum capability.

Huh, so it's that brutally simple..

I was hoping there would be some magic input voltage sensing level circuit which would adjust the level accordingly but that 1st opamp is probably a buffer as it has 0 gain and IC301 is Toshiba chip TC9495N for volume control based on digital serial input, so no luck there.

Btw, NJM5532 opamp (both are the same, buffer and one with 16dB gain) can easilly output 12.6V but my amp, which has input sensitivity of 1V, woudn't be very happy about it.

My guess would be that amps also don't have any input overload circuit that attenuates too high input signal?