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SpecificationPhysicalWidth: 88 mm.Height: 38 mm.Length: 130 mm.Weight: 235 g (without batteries).InputSocket: mini jack 3.5 mm stereo.Input impedance: 50 k.Maximum input signal amplitude: 5 Vp-p.Voltage gain: 3.OutputSocket: mini jack 3.5 mm stereo.Rated peak output power (1 kHz sine wave, THD less than 0.01%):16 load: 50 mW24 load: 75 mW32 load: 100 mW60 load: 150 mW100 load: 160 mW300 load: 55 mW600 load: 25 mWRated power bandwidth: 10 30 000 Hz (3 dB power)THD at rated power (32 load):Less than 0.01% at 1 kHzLess than 0.05% in the whole passband.Power SupplyType: USB 5 V (via micro USB type B socket) or 3 AAA cells inside, rechargeable (NiCd, NiMH) or single use (zinc, alkaline).Batteries cut-off voltage: 2.7 V (0.9 V per cell).Estimated battery operation timealkaline 1000 mAh cells: 30 hoursrechargeable 750 mAh NiMH cells: 20 hours.Supply current, 32 headphones (for batteries supply current depends on discharge level):idle (no signal): 16 mA from USB, 24 mA from batterieslistening to pop music, loudly: 30 mA from USB, 35 mA from batteriescontinuous 1 kHz sine wave at 50 mW RMS: 175 mA from USB, 180 mA from batteriesThe amplifier may be powered from USB or from batteries. It has a standard micro USB type B socket, the same as used in most of smartphones and tablets. Power requirements of KA71 are low, so it may be powered from any desktop computer, laptop, USB hub, phone charger or powerbank, using standard USB type A to micro USB type B cable. The amplifier only uses USB power, data lines are not connected inside.In case when batteries are inserted and USB power is connected at the same time, batteries are automatically disconnected, so the device works on USB power. Then there is no need to remove batteries each time USB power is used.BatteriesKA71 uses three AAA size batteries. Accepted types are single use zinc or alkaline batteries, as well as rechargeable NiMH ones. To insert or replace batteries:Disconnect all the cables, switch off the power switch.Unscrew two front upper screws. Use a screwdriver with Phillips size 1 (PH1) tip.Unscrew two rear upper screws.Pull the upper half of enclosure up. It is not connected to anything.Remove old batteries if any (new amplifier comes without batteries installed).Insert new batteries, observing polarity, which is shown on the holder. If not sure, negative terminals should contact with springs.Put back the upper half of enclosure. Note that it only fits one way, you may need to turn it by 180.Carefully screw in the screws. Note that a steel screw may damage aluminum thread easily. Start with bare hand, use screwdriver after making a few turns. Avoid excessive tightening.Verify that power LED lits when the power switch is switched on.Remember:Even if you use rechargeable batteries, they are not being charged while USB power is connected. To recharge them you have to remove them from KA71 and use a standalone charger for NiMH batteries.Do not keep discharged batteries inside the device for a long time. Battery leak may seriously damage the amplifier.
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