Samson QH4 4-Channel Headphone Amplifier - Manual (Page 6)

9. To expand the QH4 to allow for more than four individual headphone
outputs, you can connect multiple QH4 amplifiers together by plugging a
1/8” stereo cable into the Aux Output of the first QH4 amplifier and the
Aux Input of another QH4 amplifier. You can repeat this step to add as
many headphone amplifiers as necessary. The Aux Output jack is after the
MASTER Volume/Power control, Mute and Mono switches, so all adjust-
ments to these controls will affect units further down the chain.
If you have connected different models of headphones to the QH4,
you may find that some require more gain than others to achieve the
same volume. This kind of disparity occurs if the headphones have
different sensitivities or different impedances. The lower the imped-
ance, the louder the headphone will sound compared to another,
higher impedance headphone at the same volume setting. Sensitivity
is measured by determining the decibel (dB) level generated by 1 mW
of power input. The higher the dB rating, the louder the headphone
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