Simplistic NJFET RIAA

[merlin el mago]

I will try to calculate:

Scope set 0.2V/cm
Direct 1kHz generator aprox. half cm = 0.1Vpp
After Low MC pre-pre aprox. 2 cm = 0.4Vpp
This gives me 12.0412 dB not 20dB

Are my calculations OK or wrong?

[Salas]

Originally Posted by merlin el mago

Voltage gain in dB = 20 log Vout/Vin

Now I only need to know how calculate the volts with the scope, help please?

You need see 10X the input but don't feed it 100mV, feed it 1mV. If you don't have the means try it on the actual TT.

[merlin el mago]

1st pic direct 1kHz aprox. 1mV, 2nd pic right channel after pre-pre, 3rd pic left channel after pre-pre.

[Salas]

When you feed from gen's Zo Ohm to cart load value, better tap off to scope as you feed the pre so to be sure what actual input remains when comparing output to the other channel. What is the signal source impedance and what is the input pre-pre's load?

[merlin el mago]

Signal source audio generator impedance 600 ohms, input pre-pre load 220 ohms.

[Salas]

Thus you lose much input signal when you apply VS what you prepare on 1Meg scope input.

[merlin el mago]

Sorry my ignorance how do you say: "what you prepare on 1Meg scope input"

Do you want that I do the measurements with the probe x1?

[Salas]

Its simple. 600 Ohm to 220 Ohm form a 1/3.7 Lpad. So you lose much of your signal that you saw on 1 MegOhm scope channel before. To have 1mV pk-pk (0.35mVRMS) on the pre, see 3.7mV pk-pk on your scope directly from your generator first.

[merlin el mago]

That's 3.7mVpp, probe x10 direct audio generator to scope, scope set 10mV/cm scale, audio generator attenuation 30dB

[Salas]

If you will see 1 division output with that signal and 10mV/div, probe X10 your pre has 20dB gain.