Yes, I am trolling.
I've been trying to learn as much as I can about audio electronics these last few years, and have built some tube audio circuits that I've decided are keepers. I started back in the 1980s with mainstream 'good' solid-state gear, worked my way up to a complete Audio by Van Alstine (AVA) setup, with one of their SuperFET preamps, a MOSFET 100C amplifier, B&W speakers and a harman kardon T60C turntable with Grado cartrdige ("Longhorn" version from AVA). Sometime around 1990, I was introduced to a little shop called "Fi" on Watts St. in NYC. That blew my mind.
A few years ago, I was introduced to "Valve Amplifiers" by Morgan Jones. (http://www.amazon.com/Valve-Amplifiers-Fourth-Edition-Morgan/dp/0080966403) Mr. Jones methodically tests vacuum tubes for distortion and noise, and shows he can easily get less than 0.1% harmonic distortion at line level from several common triodes. He also demonstrates that this distortion is practically all composed of 2nd harmonic distortion, at least for the better performing triodes. This is all open loop, without negative feedback wrapped from output to input to linearize the stage. You can't add quite as much negative feedback (NFB) to a vacuum tube as you can to an opamp or FET stage, but -10dB of NFB should be attainable. Mr. Jones also shows that if the open loop distortion of the stage is already low, and is of predominantly 2nd order harmonic, NFB will not generate noticeable higher order harmonics when applied. In other words, adding NFB to an already clean circuit will only make it cleaner. Therefore, a vacuum tube stage can be made to have less than 0.05% total harmonic distortion, with not much trouble. 0.01% THD should be attainable, with care.
So my question is, does an opamp stage (such as is common now) have orders of magnitude lower distortion than this, in actual practice, at line level (let's say 100mV rms input to 2V rms output)?
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I've been trying to learn as much as I can about audio electronics these last few years, and have built some tube audio circuits that I've decided are keepers. I started back in the 1980s with mainstream 'good' solid-state gear, worked my way up to a complete Audio by Van Alstine (AVA) setup, with one of their SuperFET preamps, a MOSFET 100C amplifier, B&W speakers and a harman kardon T60C turntable with Grado cartrdige ("Longhorn" version from AVA). Sometime around 1990, I was introduced to a little shop called "Fi" on Watts St. in NYC. That blew my mind.
A few years ago, I was introduced to "Valve Amplifiers" by Morgan Jones. (http://www.amazon.com/Valve-Amplifiers-Fourth-Edition-Morgan/dp/0080966403) Mr. Jones methodically tests vacuum tubes for distortion and noise, and shows he can easily get less than 0.1% harmonic distortion at line level from several common triodes. He also demonstrates that this distortion is practically all composed of 2nd harmonic distortion, at least for the better performing triodes. This is all open loop, without negative feedback wrapped from output to input to linearize the stage. You can't add quite as much negative feedback (NFB) to a vacuum tube as you can to an opamp or FET stage, but -10dB of NFB should be attainable. Mr. Jones also shows that if the open loop distortion of the stage is already low, and is of predominantly 2nd order harmonic, NFB will not generate noticeable higher order harmonics when applied. In other words, adding NFB to an already clean circuit will only make it cleaner. Therefore, a vacuum tube stage can be made to have less than 0.05% total harmonic distortion, with not much trouble. 0.01% THD should be attainable, with care.
So my question is, does an opamp stage (such as is common now) have orders of magnitude lower distortion than this, in actual practice, at line level (let's say 100mV rms input to 2V rms output)?
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