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Simplistic NJFET RIAA
Simplistic NJFET RIAA
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Old 7th July 2012, 07:06 PM   #7751
merlin el mago is offline merlin el mago
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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?
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Old 7th July 2012, 07:32 PM   #7752
Salas is offline Salas  Greece
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Simplistic NJFET RIAA
Quote:
Originally Posted by merlin el mago View Post
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.
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Old 7th July 2012, 09:34 PM   #7753
merlin el mago is offline merlin el mago
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1st pic direct 1kHz aprox. 1mV, 2nd pic right channel after pre-pre, 3rd pic left channel after pre-pre.
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Old 7th July 2012, 10:04 PM   #7754
Salas is offline Salas  Greece
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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?
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Old 8th July 2012, 10:45 AM   #7755
merlin el mago is offline merlin el mago
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Signal source audio generator impedance 600 ohms, input pre-pre load 220 ohms.
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Old 8th July 2012, 12:58 PM   #7756
Salas is offline Salas  Greece
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Thus you lose much input signal when you apply VS what you prepare on 1Meg scope input.
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Old 8th July 2012, 02:28 PM   #7757
merlin el mago is offline merlin el mago
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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?
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Old 8th July 2012, 03:37 PM   #7758
Salas is offline Salas  Greece
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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.
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Old 8th July 2012, 04:12 PM   #7759
merlin el mago is offline merlin el mago
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That's 3.7mVpp, probe x10 direct audio generator to scope, scope set 10mV/cm scale, audio generator attenuation 30dB
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Old 8th July 2012, 04:53 PM   #7760
Salas is offline Salas  Greece
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If you will see 1 division output with that signal and 10mV/div, probe X10 your pre has 20dB gain.
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