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Yes, we have violated Pawel’s first rule, but at least we will not be leaving behind any widows (or widowers, I know that this webzine has at least three female readers). Because the circuit is now completely capacitor coupled, we can eliminate resistors, R3 and R4, which represented the two 150-ohm resistors and 100-ohm potentiometer in Pawel’s original circuit. Their removal will increase the gain and lower the output impedance somewhat. Still, four coupling capacitors is a bit much (each glibly draw capacitor actually represents a cluster of capacitors: a 470µF electrolytic in parallel with 10µF and 0.22µF film capacitors). The circuit below drops the SRPP affectation from the circuit by separating the differential amplifier from the output stage. DC coupling is accomplished by using two voltage dividers, which lose 33% of the differential stage’s signal, but they allow a 100-volt DC shift in the signal! To what effect? Where we were gain starved, we are only gain hungry, as the gain climbed from 0.263 to 1.32. The output impedance has fallen to 40 ohms, an eminently useable value. But the distortion is back to 1%. We are getting closer, but we are not there yet. |
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AC coupled headphone amplifier with added “Horizontal” making capacitors Download B2 Spice circuit |
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J Safe |
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TCJ Companion Software The sale of these tube audio software programs allows for the continued free reading of the journal, a means of economically justifying its existence. Plus they are great little programs at bargain prices for the audio constructor. |
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Fourier analysis of the headphone amplifier above (0.32 volts at 1kHz into 32 ohms) in B2 Spice A/D |
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TCJ horizontal headphone amplifier version 1 drawn in B2 Spice A/D Download B2 Spice A/D circuit of amplifier |