Gigahertz switching is possible with tubes (see any microwave oven!) but for audio purposes, the complexity, heat, and expense required to achieve Class D operation would negate all the value of Class D -- efficiency and small physical size -- with no benefit in return.With Class D amplifiers the outputs operate as very fast switches. Tubes can't switch on and off fast enough.
The Berning amps may not be true OTL insofar as there appears an rf impedance transformer involved.
I'm a little thickheaded today, maybe sombody more clearheaded can interpret the statement for the class.
http://davidberning.com/products/qz
Gigahertz switching is possible with tubes (see any microwave oven!) but for audio purposes, the complexity, heat, and expense required to achieve Class D operation would negate all the value of Class D -- efficiency and small physical size -- with no benefit in return.
TV "Flyback" horizontal output stages were resonant switchmode, iirc.
How difficult would it be to PWM something like this thru an integrator?
Efficiency and linearity.They were transformer coupled. That's why they have flyback transformers.
What would be the point?
They were transformer coupled. That's why they have flyback transformers.
QUOTE]
Yes, but switchmode. Not talking strictly OTL .
"Without using audio output transformers".FWIW:
The design of the Berning ZH270 power amplifier represented a radical departure from that of other amplifiers. The ZH270 was the first amplifier using all-tube amplification to properly match the high-voltage, low-current operating parameters of vacuum tubes to the low-voltage, high-current drive requirements of dynamic loudspeakers without using audio-output transformers. The technology is detailed in Berning US patent 5,612,646, and a simplified overview is given below. The ZH270 has gained much respect for its transparency, versatility, and reliability, and has enjoyed a production run of over 10 years. The ZH technology has also proven itself in other recent Berning products as well.
Even Mr. Berning says it's an OTL amplifier.
It's just an example of what can be done with tubes. Square-wave oscillators within the hundred khz to mhz range of typical Class D switching is straightforward using conventional tubes, but there's no value in doing so, and the inherent inefficiency of tubes is contradictory to the benefits of Class D.Microwave ovens use a Magnetron. It's not what anyone would call a conventional tube.
At a glance, it looks to be a solid-state DC-to-DC switch-mode converter whose output is modulated by a tube amplifier. The DC output of the converter drives the speaker.The Berning amps may not be true OTL insofar as there appears an rf impedance transformer involved.
I'm a little thickheaded today, maybe sombody more clearheaded can interpret the statement for the class.
http://davidberning.com/products/qz
The DC output of the converter drives the speaker.
The patent describes it as a DC-to-DC converter, I presume notionally isomorphic to the power rails in a conventional Class A or Class AB amplifier, but modulated as part of the converter itself.Don't you mean AC output?
Per the patent, it's achieved in a push-pull fashion with two amplifying legs. See Fig 1.Pulsating (modulated) DC will not drive any speaker I'm aware of. There has to be a conversion to AC.
Yeah, it's the size of a matchbook and rated 300 wpc, but at what distortion level?
Per the patent, it's achieved in a push-pull fashion with two amplifying legs. See Fig 1.
The little Chi-Fi amps give a tantalizing taste of what is possible, adequate ps is essential. The higher gain examples are intended to operate directly from the source without preamp.The Hypex NC400 module [a discrete build] may not be the current king of low-distortion, but it's definitely in the running.
To quote the Hypex site: "Distortion (THD and IMD) over the full audio and power range is negligible, typically below 0.0007%. Distortion at listening levels (1W) is unmeasurable."
And that's running on a SMPS.
For that matter the Class D amp I'm currently listening to is rated at 70 WPC into 8ohms at 1% THD, but actually puts out 55 WPC into 8ohms at 0.005% THD and over 100WPC into 4ohms at the same THD level.....which is plenty of low-distortion watts for my current system.
It's unfortunate that many only have experience with cheap Class D boards......often enough with too much built-in gain, running off under-powered wall warts.