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Vinyl
6L6GC Single Ended amplifier with first attempt OPT
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<blockquote data-quote="Ampdog" data-source="post: 71667" data-attributes="member: 144"><p>The first circuit gave a constant current load (well comparatively) to the triode, the cathode follower output type a constant current load followed by a cathode follower, i.e. lower output impedance. The distortion will still be a function of the lower triode's characteristics, but is usually better than with a finite (low) resistance as plate load.</p><p></p><p>Problem with this arrangement is with the greater effect of Miller capacitance on the lower triode, as governed by the input (source) impedance. In the given case there was also an unbypassed cathode resistance, further increasing the lower triode internal resistance, which will begin affecting the circuit. In that sense this circuit is less desireable as an amplifier input circuit, because of the possibly unknown source impedance - particularly as part of a main amplifier, where the varying Miller effect (input pole) can compromise feedback stability. An interesting comparison (which I have not done) will be between this circuit and using two triodes in a cascode circuit. Such a stage has high linearity but high output impedance, but mainly, the effect of the source impedance is largely cancelled as a result of negligible Miller effect, thus wider bandwidth (though depending on the following stage).</p></blockquote><p></p>
[QUOTE="Ampdog, post: 71667, member: 144"] The first circuit gave a constant current load (well comparatively) to the triode, the cathode follower output type a constant current load followed by a cathode follower, i.e. lower output impedance. The distortion will still be a function of the lower triode's characteristics, but is usually better than with a finite (low) resistance as plate load. Problem with this arrangement is with the greater effect of Miller capacitance on the lower triode, as governed by the input (source) impedance. In the given case there was also an unbypassed cathode resistance, further increasing the lower triode internal resistance, which will begin affecting the circuit. In that sense this circuit is less desireable as an amplifier input circuit, because of the possibly unknown source impedance - particularly as part of a main amplifier, where the varying Miller effect (input pole) can compromise feedback stability. An interesting comparison (which I have not done) will be between this circuit and using two triodes in a cascode circuit. Such a stage has high linearity but high output impedance, but mainly, the effect of the source impedance is largely cancelled as a result of negligible Miller effect, thus wider bandwidth (though depending on the following stage). [/QUOTE]
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Audio and Video Talk
Vinyl
6L6GC Single Ended amplifier with first attempt OPT
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