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CF after gain stage

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Just breadboarded a SV83 CCS on a simple common cathode gain stage.

After testing it successfully as a linestage, I decided to hook up a pair of headphones through 220uF output caps. Sounded reasonable.

Now what I've seen in the majority of headphone amps are CF's following the gain stage.

Is this necessary? What advantages/benefits does it give to the circuit?
 
That depends on your voltage amplifier tube and the impedance of the headphones. If the headphones' impedance is greater than about 10x the effective plate resistance of the voltage amplifier, the distortion reduction will not be large. But for lower impedances, it can be very significant- the 'phone's impedance will definitely change the slope of the effective load line.
 
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