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So if I have a phono preamp with a MC section that provides 57.5db of gain, what's the optimal cartridge output I should be looking for? I know from experience that .25mv is too low. What's the math here?
Edits: 04/03/21Follow Ups:
Just plug in your values here >
"The only cats worth anything are the cats who take chances. Sometimes I play things I never heard myself." Thelonious Monk
57.5 db, is a voltage gain of 750.
If your linestage has typical 20db gain, that adds additional gain of 10. Total voltage gain is 760. So 760 times .0025 = 1.9v. If that is too low, then your amp must have a higher input sensitivity than 1.9v, or are you using a passive linestage?
Someone is welcome to correct me if my math is wrong please.
mg16
Edits: 04/03/21 04/03/21
You've made a couple of mistakes. The interesting thing is that your two mistakes actually resulted in the correct answer; almost! ;-)The cartridge was rated at 0.25-mV. That equates to 0.00025-volts.
You can add decibel values, but you have to multiply actual gain values. Therefore, the total gain for the preamp would be 57.5-dB + 20-dB = 750 x 10 = 7500.
Preamp output voltage = 0.00025 x 7500 = 1.875-volts.
Good luck!
John Elison
Edits: 04/03/21
Thank you John for correcting my mistakes.
Time to brush up on my math.
mg16
Like Sondek implied, you need to factor in the additional gain afforded by your line stage, if you are using an active line stage.
Yes, active line stage with 17.9db of gain. Still a .25mv cartridge is not performing with it. I get plenty of volume but the signs of not enough gain are clear, lack of dynamics, no top end sparkle. Just trying to figure out for a new cartridge purchase what output I should be looking for.
You sure you've loaded it properly?
0.4 or 0.5 ought to be plenty of output, and there's bunches of carts to pick from in that range.
I'm prejudiced, but the Kiseki Purple Heart is a fantastic cart with 0.5mv output. Put it on your list.
I am kind of surprised that 57 db of phono gain plus 18db gain from your linestage is insufficient total gain for your cartridge to drive the amplifier. Most amps can be driven to full output by about 1V, give or take. Using an on-line calculator, I get about 1.4V at the standard stylus velocity, delivered from the output of your linestage to the input of your amplifier, from your 0.25mV cartridge. As mg16 suggested, you might want to check the input sensitivity of your amplifier, as well as your speaker's efficiency spec.I see JE posted almost simultaneously. He used 20db for the linestage; I used 18db. Either way, the audio signal coming out of your linestage is sufficient in amplitude to drive most amplifiers to full output.
Edits: 04/03/21
What power amp are you using? You need to know its input sensitivity, given in volts, then you can calculate the cartridge output needed to drive the power amp to a reasonable output level to your speakers.
mg16
My CAT SL1 has 58 dB of phono gain and I'm using a cart with 0.5mv output.
Have more than enough gain. Although should mention that the line section adds another 15.2 dB in the low setting.
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