Here's the
Robinette Box Instructions:
Instructions
WARNING: You must set the Amplifier Mode Switch before connecting your amplifier to the Robinette Box. An incorrect switch setting can damage a balanced output amplifier and your headphones.
Before connecting the
Robinette Box to an amplifier set the Amplifier Mode Switch' to match the amplifier you are connecting to. The switch is used to switch between amplifiers with single-ended output and amps with balanced output. The switch only needs to be changed when moving the
Robinette Boxto a new amplifier. The switch has a latching lever to prevent accidental movement so the lever must be pulled outward slightly to change switch positions.
Set the Amplifier Mode Switch
1. Single-Ended Output Amplifier. Switch lever toward TRS headphone jacks. Use this position for amplifiers with single-ended output (common ground). All three headphone jacks are active.
WARNING: Only use this switch position when connected to an amplifier that has its black speaker terminals tied together (common ground or single-ended). Selecting this position while connected to an amp with balanced output can damage your headphones and amplifier. You can verify the amp's black speaker terminals are tied together by using a multimeter's continuity test. With the amp unplugged touch the multimeter's probes to the black speaker terminals. If you get the continuity beep your black speaker terminals are tied together and it's safe to use the single-ended amp switch position. If you do not get continuity your amp has balanced output and you should not engage this mode. Your amp's schematic diagram will also show a ground symbol connected to the black speaker posts. More info on balanced versus single-ended amplifier output can be found here.
2. Balanced Output Amplifier with Balanced Headphones. Switch lever centered. Use this for amplifiers with balanced output (non-common ground).
Only the XLR jack is active. The TRS headphone jacks' combined ground is disconnected to protect the amplifier.
3. Balanced Output Amplifier with Single-Ended Headphones. Switch lever toward XLR jack. Use this position when you need to use single-ended headphones with an amplifier that has balanced output. The balanced amplifier is protected from the TRS jacks' combined ground by resistors R5. All three headphone jacks are active.
Set the Network Bypass Switch to the Down position (resistor network active)
Switch Up = Network Bypass. XLR and TRS connectors are directly connected to the speaker binding posts.
Switch Down = Resistor Network Active. Attenuation L-pad 'Preferred Resistor Network' is switched into the circuit.
WARNING: The headphone volume will jump by 12.4 decibels when the Network Bypass Switch is moved to the Bypass position. Turn the amplifier volume down before selecting the Bypass position.
Note: With the Network Bypass Switch down (network active) it is safe to run your amplifier with no headphones connected because the amplifier will be given an 8 ohm load by the resistor network.
Connect the Robinette Box to your amplifier
With the Amplifier Mode Switch set properly connect the box to your amplifier's speaker terminals. The
Robinette Box speaker binding posts will accept single and dual banana plugs, spades and raw wire up to 10 gauge. When viewing the box from the front (the end with headphone jacks) the right speaker posts are on the right and the left are on the left. The upper binding posts are for the amplifier connection, the lower binding posts are optionally used to connect your speakers.
Connect your headphones to the Robinette Box
Turn your amplifier volume full down then power it up
Turn the volume up slowly to keep from overpowering and possibly damaging your headphones. Remember to turn the amplifier volume down before changing position of the Network Bypass Switch.
Enjoy your headphones and speaker amp
The
Robinette Box is
open source hardware under the
Creative Commons permissive license and is open to royalty-free commercial use.
