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In Reply to: RE: non-inverting preamp w/schematic ... posted by Triode_Kingdom on June 17, 2017 at 11:08:09
I made some adjustments to the schematic that resulted in more gain, lower THD% but slightly higher Zout.
Without the SubOut and 4.7K isolation resistors, Zout @ 20Hz = 5.8K & Zout at 1KHz = 4.9K.
I needed 23dB of Gain to drive my SE 6CB5 triode amp into clipping, so this circuit works OK for that.
Didn't have room on my preamp chassis to add a follower, but with short cable runs in my system, it does not sound like I needed it.
I set my volume pots at 8-9 o'clock for average listening.
Subjectively, I find no issues with sound quality so far.
Thanks to all for comments and ideas.
Does LT Spice calculate impedance for you?
If so, whats the method?
The formula is just ohms law.
You need to set an AC current source at the output, do a small signal AC analysis from the simulate command.
Use a linear BODE plot for the left vertical axis ohms magnitude.
Look at the schematic for the Spice commands.
Hope that helps.
The easiest method is to set the main excitation voltage to zero and drive the output with a one amp AC current. Then you plot the voltage at the output and view it on a linear scale and the output in volts will be the output Z in ohms.
If it makes you feel better you can enter an expression to divide the voltage output by the Current you will get the impedance listed in ohms on the vertical scale.
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