The TX-NR807 has seven powerful 135-watts-per-channel Onkyo WRAT (Wide Range Amplifier Technology) amplifier sections for high output and low distortion, offering a dynamic power rating of 300 watts into 3 ohms.

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To explore this, I switched to using Beyerdynamic DT 990 Pro over-ears with a high impedance of 250 ohms and found that the difference was obvious: the iPhone 4 and 4S were the only devices to provide sufficient volume in quiet recordings using these headphones.

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