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Audio and Video Talk
Audio Visual Technology
Attenuation vs. 'Gain Control'
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<blockquote data-quote="Steerpike" data-source="post: 865222" data-attributes="member: 807"><p>^^^ There's where the mumbo-jumbo enters.</p><p></p><p>Variable transconductance amplifiers are REALLY old hat... Leon Theremin was using them in his musical instruments in the 1920s. And vari-u valves have been used in just about every AM radio since the start of time.</p><p></p><p>The way a transconductance amplifier's gain is changed is by varying a fixed DC bias current through a specific transistor (or valve) configuration. To this end, the "quality" of that control signal is irrelevant (as long as it isn't seriously noisy). You don't need a magically high-end rotary switch with resistors touched by the Pope, because that is only valid if you are putting the actual audio signal through such components: in this case they claim to be putting only the control signal through the Holy Rotary Switch of Antioch.</p><p></p><p>Variable transconductance amplifiers are less linear than an equivalent circuit with fixed transconductance, so they are not the ultimate in audio building blocks - they just solve one specific requirement, at the expense of some others.</p></blockquote><p></p>
[QUOTE="Steerpike, post: 865222, member: 807"] ^^^ There's where the mumbo-jumbo enters. Variable transconductance amplifiers are REALLY old hat... Leon Theremin was using them in his musical instruments in the 1920s. And vari-u valves have been used in just about every AM radio since the start of time. The way a transconductance amplifier's gain is changed is by varying a fixed DC bias current through a specific transistor (or valve) configuration. To this end, the "quality" of that control signal is irrelevant (as long as it isn't seriously noisy). You don't need a magically high-end rotary switch with resistors touched by the Pope, because that is only valid if you are putting the actual audio signal through such components: in this case they claim to be putting only the control signal through the Holy Rotary Switch of Antioch. Variable transconductance amplifiers are less linear than an equivalent circuit with fixed transconductance, so they are not the ultimate in audio building blocks - they just solve one specific requirement, at the expense of some others. [/QUOTE]
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Audio and Video Talk
Audio Visual Technology
Attenuation vs. 'Gain Control'
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