AoE x-Chapters, High-Speed op-amps section, DRAFT

[Johnny B Good]

On Wed, 17 Jul 2019 07:31:56 +0000, Jan Panteltje wrote:

====snip====

https://youtu.be/lMuJKsUjD_o

Would not like to stand there.
OTOH his camera has no problems it seems,
is just RF HV being rectified, AM station?

It's not rectification as such. The "detection" in this case is simply a
matter of the plasma in the arc modulating the air pressure, translating
the sampled modulated RF carrier power into sound waves directly.

It's the principle used in exotic "massless" argon arc loudspeaker
transducers in the rather more expensive Hi Fi setups where the audio
signal amplitude modulates a high frequency carrier (typically 100KHz or
more) which generates a very high voltage (high impedance constant
current source) across the arc gap electrodes.

The difference in this case being the use of less than 80 or 90 percent
modulation depth to avoid the arc becoming extinguished during negative
modulation peaks at the LF end of the audio baseband feeding the
modulator circuit, which is the reason why the arc in those videos kept
dropping out, necessitating a re striking of the arc from time to time to
resume the effect (and also why it tends only to be applied to plasma arc
driven "tweeters").

--
Johnny B Good

 

[Jan Panteltje]

On a sunny day (Mon, 29 Jul 2019 21:17:16 GMT) it happened Johnny B Good
<johnny-b-good@invalid.ntlworld.com> wrote in
<wnJ%E.685874$Cb4.300233@fx07.am4>:

On Wed, 17 Jul 2019 07:31:56 +0000, Jan Panteltje wrote:

====snip====

https://youtu.be/lMuJKsUjD_o

Would not like to stand there.
OTOH his camera has no problems it seems,
is just RF HV being rectified, AM station?

It's not rectification as such. The "detection" in this case is simply a
matter of the plasma in the arc modulating the air pressure, translating
the sampled modulated RF carrier power into sound waves directly.

It's the principle used in exotic "massless" argon arc loudspeaker
transducers in the rather more expensive Hi Fi setups where the audio
signal amplitude modulates a high frequency carrier (typically 100KHz or
more) which generates a very high voltage (high impedance constant
current source) across the arc gap electrodes.

The difference in this case being the use of less than 80 or 90 percent
modulation depth to avoid the arc becoming extinguished during negative
modulation peaks at the LF end of the audio baseband feeding the
modulator circuit, which is the reason why the arc in those videos kept
dropping out, necessitating a re striking of the arc from time to time to
resume the effect (and also why it tends only to be applied to plasma arc
driven "tweeters").

Nice explanation, thanks.
As to that sort of 'high end' audio, my little piezo tweeters do fine.
The normal tweeters do even better (less distortion), and at my age I
cannot hear much above 10kHz anyways

The Quad electrostatic speakers is the best I ever heard,
used in those days in the TV studio sound control rooms as monitor:
https://en.wikipedia.org/wiki/Quad_Electrostatic_Loudspeaker