new GAN amplifier

Sorry, just a correction there @arty_vandelay it’s EPDR (Equivalent Peak Dissipation Resistance.) for those who want to know the complete title.

Here is a snippet from the measuring labs used by HiFi News and Record Review, also used I believe Absolute Sounds use as well. And Stereophile’s John Atkinson also mentions it from time to time when things get into the hairy load area.
https://ibb.co/qxjtkn7

https://www.stereophile.com/content/heavy-load-how-loudspeakers-torture-amplifiers-page-2

Cheers George

Thanks George, my bad - typo.

Typically, in "eng" speak impedance is expressed as a value with a phase angle (polar form) or real + reactive (rectangular form).

EPDR is obviously a means of expressing power dissipated in the amplifier based on instantaneous values of voltage and current at a specified frequency. In other words, a reverse engineered value. 

Bingo arty_vandelay. However, it is specific to linear amplifiers where that instantaneous voltage represents a large voltage drop across an output device operating in the linear region at a given current and hence high instantaneous power. As the output devices in Class-D are not operated in the linear region, it has little meaning.


What EPDR hits really hard is BJT output stages as BJT devices have secondary breakdown mechanisms impacted by instantaneous power (or accurately power and voltage), even if they can handle the current delivery.

arty_vandelay23 posts11-24-2019 8:43pmEPDR is obviously a means of expressing power dissipated in the amplifier based on instantaneous values of voltage and current at a specified frequency. In other words, a reverse engineered value.

arty_vandelay

Yes, if the Wilson Alexia didn’t have a negative phase shift of -45’ degree in the bass causing an EPDR of 0.9ohm, then it would be an easier load for the amp to drive, but still it would be 1.8ohm and still needing an amp with good current delivery. Definatly not OTL or P/P tube or even most complimentary n & p channel Mosfets, unless they are push pull N channel only, then those can get some current going, like the Solution amps (or similar) I believe.

Cheers George

georgehifi,
EPDR does not define "difficulty" to drive the load per-se, even though it was defined that way in consumer audio media. It is illustrative of the thermal stress that is put on the amplifier output devices instantaneously. The peak current at the worst case EPDR is not the peak current of the amplifier.

Good current delivery with complimentary P-Channel is certainly possible, but better performance these days can be done with N-channel so that is normally the preferred architecture.

Note that MOSFETs don't have secondary break-down effects, hence EPDR is not nearly as critical for FET output stages. They don't mind high instantaneous power.