Gain of line preamplifier

10-24-14: Czarivey
Manufacturers instead of gain would often provide you input sensitivity and max output voltage. 2 ways can be worked around this problem:
1. Contacting manufacturer about gain info
2. Use following formula to calculate gain:
a) Max_Voltage * 0.707 = RMS Voltage
b) 20Log(RMS Voltage/Input Voltage)

I'm not sure this is correct. For preamps and line stages, when input sensitivity is specified it usually represents (with the volume control set at max) the input voltage required to drive the output to an indicated level, such as 1 volt, that is representative of a realistic operating condition. Not the input voltage required to drive the output to its specified maximum. The specified maximum is the maximum output voltage the preamp or line stage is capable of providing without clipping or gross distortion, and would usually and hopefully be a far higher voltage than would ever occur under normal operating conditions.

You may be thinking of power amps, where the specified input sensitivity usually represents the input voltage required to drive the amp to its rated maximum output power.

Also, I believe that maximum output voltage specs for preamps and line stages are usually expressed in rms terms, not peak, so the 0.707 factor would usually not be applicable.

Regards,
-- Al

P.S: An example of what I am describing would be these specs for the Parasound JC2:

Input Sensitivity:
200 mV for 1 V output
Total Gain: 14 dB
Maximum Output: 8 V

Note that 20log(1 volt/200 mV) = 20log(1/0.2) = 14 dB, corresponding to the indicated gain.

Regards,
-- Al

"Variable output impedance is heavy disadvantage of any passive preamp even if you have substantially high input impedance of your amplifier."

Please give your reasons why (using laws of electronics)

1: If using a low (<100ohms) source impedance (which most are).

2: Into a 10kohm passive pot with 1mt of low capacitance interconnect (which most good ones are).

3: Into a power amp with 47kohm or higher input impedance (which most are)

"Nelson Pass would also agree with me."

Your assuming a lot with this bold statement, quoting words that Nelson Pass has never made. In which he's been quoted to say the opposite 6 posts back.

Cheers George

George,
I've never quoted Nelson Pass. If 1,2,3 are true, than probably it's a world of dreams. In the real world it's all vary, but far not "most good ones".

"Nelson Pass would also agree with me"

If that's not putting words into Nelson mouth, I don't know what is.

Cheers George