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Impedance optimization - Page 3

post #31 of 35
8/26/09 at 3:08pm
Just the opposite!! If that were true:

Take for example the 26 ohm Denon D5000 (106dB/mW) or D7000. They are rated at 1500mW. So he should have more power there.

The AKG K702 (105dB/V - I don't know what that is in mW) which are 62 ohm are rated at 200mW, so he should have less power there.

The Sennheiser HD800 (102dB/mW) which are 300 ohm are rated at 500mW, so he should have less power there.
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post #32 of 35
8/26/09 at 3:14pm
But you are talking about output POWER, not current delivery (they are different). Wasn't KIS suggesting that is was current delivery that was being limited?
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post #33 of 35
8/26/09 at 3:20pm
Low impedance phones require more current. High impedance phones require less current. We're still talking about the driving power of headphones. So I don't see why Kingwa would limit the current for lower impedance loads. It seems contrary to the specs of most every other SS headphone amp.
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post #34 of 35
8/26/09 at 3:25pm
Again just guessing about his reasons, but for precisely the reason you state - low impedance headphones might demand more current than the output devices are rated to deliver (with acceptable distortion, heat, etc.), and so Kingwa is limiting that, which means that there is somewhat less output power into that low impedance load.

Just to hold the power deliver constant at 300mw, when the load impedance drops from 100 to 25 ohms, the amp would have to very significantly increase it's current delivery, and it's quite possible that it simply cannot safely deliver that much current.

One last point (sorry to keep editing this post) - the SS output devices that deliver the most current may not necessarily be the best sounding, which might explain what Kingwa is up to
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post #35 of 35
8/26/09 at 3:43pm
Quote:
Originally Posted by IPodPJ View Post
I wonder why the hell he would do that then. Why not keep the output power proportional across the board, like everyone else does?
Well, it is a headphone amp after all.

If it wasn't for current limiting, and if it were driving some 8 ohm loudspeakers, it would be the equivalent of a 72 watt power amp, if only for a second or two.

The power rating figures ultimately reveal its maximum voltage output (higher impedances) and its maximum current delivery (lower impedances). And the figures are pretty much meaningless in any sort of practical sense. I mean, you're never going to be driving any headphones with the amp's full 24 volt output capability, nor are you ever likely to need more than 200 mA.

If you reference power to something more reasonable, say, 5 volts out, then everything's just fine:

25 Ohms: 1 Watt
62 Ohms: 0.4 Watt
100 Ohms: 0.25 Watt
300 Ohms: 0.083 Watt
600 Ohms: 0.042 Watt

k
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