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Honestly I don’t know what reasonable headphone output today has these high output impedances. They’re all class D amplifiers with quite low impedance directly
by Kirby64 3y ago
Honestly I don’t know what reasonable headphone output today has these high output impedances. They’re all class D amplifiers with quite low impedance directly to the power supply. This 1/8th rule is kind of pointless… you just specify output voltage drive at various loads and measure frequency response. Most do this very well. No need to faff about with damping of responses.
- atoav 3y agoJup, but when the post was written good class D headphone amps weren't as readily available as it is today, if I recall correctly.
- pclmulqdq 3y agoClass A and AB amps often have significant output impedance due to how they are constructed, and used to be the standard. They still are the standard for HiFi audio. The other types of amps are generally pretty low impedance. Edit: Amp types as pointed out by another commenter.
- smolder 3y agoI wouldn't call Class A "standard", unless you're including class AB in that? Pure class A is a bit esoteric since it's wildly inefficient compared to D or even AB.
- kazinator 3y agoClass AB amplifiers (basically class B but with an overlap region when switching between the output devices) have very low output impedance when they feature negative feedback. Which is the standard for hi-fi audio.
- kazinator 3y agoI also never heard of this 50-ohm-1996 thing. Any headphone output worth its salt in the last 70 years is going to have near zero ohm output impedance. Some headphone amplifiers use cheap integrated circuits that can only drive outputs no lower than around 150 ohms, like the JRC4556 (a device that NavGuy has written quite a bit about, incidentally). I suspect that's where that idea might come from? If you have a JRC4556 that doesn't go lower than 150 ohms, and the headphones are 32 ohms, you can pad in some series resistance to make up the difference.