blorg t1_je9xtpk wrote on March 30, 2023 at 2:13 PM

Reply to comment by exdigguser147 in Really enjoying my new $350 "budget" setup. HD660S and Topping DX1 by Jfox8

The Topping DX1 does 51mW @300Ω - 280mW @32Ω.

This is fine for the HD660S but it's nowhere near 1.5W.

Now obviously you can make a single ended amp that does 1.5W. But particularly in these small USB-powered devices, it seems easier/cheaper to get more power with a balanced output than increasing the power on single ended.

Everything else being equal, you get double the voltage balanced, which is 4x the power theoretically (and usually you'll get that into higher impedances) and typically at least 3x at lower impedances when you consider current limitations. This is a significant difference and will be audible if you need a headphone that needs the power.

Nothing about this is saying you need balanced rather than single ended for a given power level or that you need over 1.5W for most headphones (my HE6SE, Hifiman do recommend 2W@50Ω though, and I think it sort of needs this). Just that balanced does typically give substantially higher power and that is audible if you need it.

exdigguser147 t1_jea913z wrote on March 30, 2023 at 3:34 PM

They recommend an amp that does 2W @50Ω because amps are not rated for power in a standard method that accounts for the full frequency range. The headphone still only needs 1.5W max for 115db and that's 750mW per driver.

I dont know what you are on about with balanced = double voltage which means 4x power. Did you read that somewhere and not question it? Balanced does double the voltage, but the current does not change so power is only doubled.

You are applying opinions and feelings to physics.

blorg t1_jeag0v3 wrote on March 30, 2023 at 4:20 PM

The current does change though, current is proportional to voltage (Ohms law).

Double the voltage, double the current.

Power is the product of the voltage and current (Watt's law).

But you double one, you double the other. So double the voltage = double the current and as both are doubled, the power increases by the square of the voltage.

2V @ 300Ω = 13.3 mW
4V @ 300Ω = 53.3 mW

And this is actually the typical power you get out of 2V single ended / 4V balanced stuff.

Look for example here at actual measurements of the Moondrop MoonRiver 2 which does max 2V SE, 4V balanced.

At 300Ω, it is able to reach the full 2/4V without clipping and does ~13mW single ended, ~53mW balanced. At 68Ω, it's still hitting the full 2/4V and the power is ~59/235mW. The balanced power in both these cases is 4x exactly. So any headphone over 68Ω, you will get 4x the power on the balanced.

At low impedances, there can be a limit to current, so the amplifier will clip and you won't get 4x. You can see this here with 32Ω, where it gets 125mW single ended but only ~250mW balanced- and it then clips and distorts, rather than running out of voltage as in the other cases.

But you typically will get the full 4x at double voltage, into higher impedances.

Exactly how much at a given impedance depends on the design of the amp. But 4x is the theoretical increase in power, if current is not a limiting factor. And it typically won't be, into higher impedances. Check the spec sheets for some other amps with both, like the Topping A90D, you can see that 250mW SE but 1,000mW balanced into 300Ω. If you go all the way down to 16Ω, it's less, it's 3,300mW vs 9,800mW, i.e. 3x. Because there's a current limit. It's still over 2x though even at 16Ω.

exdigguser147 t1_jeahfqx wrote on March 30, 2023 at 4:29 PM

Ok, that's all well and good... you taught me something.

But there is no single driver in a headphone needing more than 750mW of power so my original point still stands, a headphone does not need or benefit from a balanced output.