Check the listing for details. Telephone Headset Amplifier DAX-275. Condition: New. Listed at 9.95 USD. Telephone Headset Amplifier DAX-275. Condition is "New". Shipped with USPS Priority Mail. Features: 1.Mute button (Battery test) Press the button to cut off the microphone temporarily. Just depress the button to resume communication with your caller. If the battery test indicator does not light by pressing mute button, replace all the batteries. (Operation battery life: not less than 2,000 hours) 2. Listening volume controller You can increase or reduce the volume of your callers voice. 3. Handset/Headset button Press it for handset use and depress it for headset use. 4. Battery test indicator Press mute button, if it does not right, replace all batteries. 5. Tone controls switch Set the tone control switch to be soften or normal. 6. External power supply jack You can use AC power adapter (3V DC) instead of battery. 7. Handset jack (handset) Connect your handset to this jack. 8. Telephone jack (Tel) Connect a telephone curly cord supplied between the handset jack of your telephone and amplifier. 9. Stereo jack for recorder The stereo plug of recorder can be connected (option). 10. Telephone compatibility switch Compatibility setting between telephone and amplifier. 11. Headset compatibility switch Select the knob to the left or right until you can hear. 12. Dip switch For transmission level and dynamic microphone.