On Thu, Feb 20, 2025 at 12:17 PM, Jerry Lee Marcel wrote:

BTW, source-follower it is not. It's actually a common-source stage.
A source fiollower has about unity gain, this common-source has about 15dB gain.

No, it is a source follower.? Its voltage gain is unity.? Input applied to gate, output from source pin.? Almost the same output voltage, but shifted 4.2 V lower.

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The overall circuit has voltage gain (~23 dB), but all of that comes from the 12AU7, in its common-cathode configuration.

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I wonder why you saw only 15 dB gain, and why you saw that in just the MOSFET.

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Not that the following has any significance - but I vaguely recall reading about operating valves (vacuum tubes) at much lower than "normal" anode voltages.? ?There were specialized miniature valves designed for it.? But it was also applied to more traditional valves too, ones like the 12AU7 that are capable of hundreds of volts.? It does not appear to be a sure-fire way to generate distortion, as this simulation demonstrates, if you trust the SPICE models.? I can't recall what were the advantages (if any) of using such low voltages - other than easier battery power.? Lower noise?? ?Longer life?? I dunno.

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Andy

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