KHE + Universal Audio OX Top Box
This guide explains to how to use the Universal Audio OX Amp Top Box in combination with the KHE Amp / Cab Switcher. Make sure to read this guide and all product manuals in great detail before hooking things up. If incorrectly connected or used, the equipment may be damaged. Better be safe than sorry!
The OX is best connected to the KHE’s Attenuator Insert Loop, which is a serial insert point between the KHE’s amp output bus and the speaker cabinet bus. This enables to:
Use the OX as a global attenuator with all connected amps and cabs
Use the OX as a load box for silent operation
Use the line out with an audio interface for recording and IR processing
All functions of the Universal Audio OX Amp Top Box can be used as normal with the KHE amp switcher.
Wiring & Setup
The OX Box is best connected to the KHE Attenuator Insert Loop. This is a serial insert point between the amp outputs and the speaker cabs. By default, the KHE’s Attenuator Insert Loop is deactivated. If not activated, the attenuator won’t work correctly. See more on that later in this guide.
Important: Before connecting the OX to the KHE, make sure the KHE and all amps and cabs are all working correctly. It’s crucial to be methodical during the setup. Start with the most basic KHE setup possible (only amps+cabs, no pedalboard or attenuator) and add things step by step.
Connect the red OX FROM AMPLIFIER jack to the white KHE S-LINE SEND jack by a speaker cable. This sends the amp speaker output signal of the KHE to the input of the OX Box.
Connect the black OX - TO SPEAKER jack to the white KHE S-LINE RETURN jack by a speaker cable. This sends the attenuated amp signal from the OX back into the cabinet switching section of the KHE. For the Impedance Switch settings, see all details further down below.
Power-On the KHE and the OX. Do not power-on the amps. Turn the master volume of the OX and amps down.
Activate the KHE Attenuator Loop in the System Menu after connecting it. If not activated, the attenuator won’t work correctly. See this link: How to activate the KHE Attenuator Insert Loop
Activate an Amp + Cab on the KHE and slowly increase the volume of the amp and the PS and test everything in detail.
The system is now ready to use.
Alternative Wiring Variants:
Single Cab or Load Box: If the OX is only used with a single cab, or as a load box with its internal load and no speaker attached, connect it to a red KHE CABINET jack. For the KHE ACS 4x2, this wiring is the only connection variant.
KHE ASX / CSX: Connect the ASX CAB MAIN to the OX Amp Input. Connect the OX Speaker Output to the CSX Speaker Input. Use speaker cables. See more information in the ASX CSX user manual.
Basic KHE + OX Box Operation
Attenuator Operation
To use the OX as an attenuator, set the OX power switch to ON and make sure to have the KHE Attenuator Loop activated. Use the OX SPEAKER VOLUME knob to set the master output volume of the rig. Use the KHE’s amp and cab switches to freely choose any amp or cab at the push of a switch (no need to stop playing, the KHE takes care of the switching and muting). Always have the OX powered on (otherwise it provides a 16 ohm safety load).
Silent Operation (Load Box Mode)
For Silent Operation with the OX in the KHE’s Attenuator Insert Loop, simply set the OX SPEAKER VOLUME to 0 so it operates silently. On the KHE, a cabinet must always be activated, but it won’t receive any signal from the attenuator. Alternatively, if the OX is exclusively used as a load box with no speaker cabs at all, it is best connected to the KHE’s Cabinet Switching Outputs (red CAB jacks).
Attenuator Bypass
The OX does not have a attenuator bypass switch and the KHE can also not bypass the attenuator. Deactivating the KHE Attenuator Loop does not bypass the the attenuator. Learn more: ACS Attenuator Loop Guide
Impedance Setting
Set the OX’s IMPEDANCE knob to match the impedance of the amplifier outputs. Similarly, the total impedance of the speaker cabinets should should match the OX’s IMPEDANCE knob setting. Learn more about impedance and impedance mismatch in the KHE Impedance Guide.
ROOM, IR, Line Out, S/PDIF, USB & Headphones
All these knobs and features can be used as normal.
Device Position in the Room
In some situations, being close to the attenuator or load box with the guitar can result in a high-pitched squealing noise. This happens due to the high magnetic field generated by the inductors and transformers of the attenuator or load box, causing feedback with the guitar pickups. Try physically separating them and avoid standing too close to the device with your guitar. You can find additional information in this Video by Fryette Amplification and in this Blog Post by Two Notes Audio on the topic. Make sure to provide proper cooling airflow for the attenuator or load box.
Power-On Sequence
All amps + KHE + OX power off > KHE power on > OX power on > Amp Heads on with standby for 2 minutes > KHE activate AMP > Ready to rock!
Power-Off Sequence
Deactivate KHE Amp+Cab > Amps power off > OX power off > KHE power off > Good Night!
Load + Switching Power Rating
The UA OX Amp Top Box reactive load box is rated for 150W RMS 200W Peak. The KHE has a maximum power switching rating of 150W. Learn more: KHE Maximum Amp Power Rating
Transistor & Solid-State Amps
The UA OX box and the KHE can safely be used with transistor & solid-state amplifiers (many other attenuators can’t). When using solid-state amps, make sure the maximum output power does not exceed 150W to avoid damage to the OX and KHE. See the OX User Manual Page 9 for more information.
Activating the KHE Attenuator Loop
The KHE Attenuator Insert Loop can be activated in the KHE System Menu. By default, the attenuator loop is turned off. It needs to be turned on for the attenuator to function properly.
Connect the attenuator to the white KHE S-Line jacks as shown in the diagram. Turn down the volume of the attenuator and the amps.
Power on the KHE. If the attenuator has a bypass switch, set it to active.
Enter the System Menu by pressing the KHE CTRL button for 3 seconds, then release it. The CTRL light starts to blink 1x, indicating “Page 1 - System Functions” is active. “Page 2 - MIDI Menu” would have 2x blinks of the CTRL light. To flip the menu page, short-press the CTRL button. The attenuator loop control is on “Page 1 - System Functions”.
Press Switch AMP 4 to activate the attenuator loop in the System Menu. If the light of amp 4 turns ON, the loop is activated. If AMP 4 light blinks 4 times, it means no attenuator no attenuator was detected by the KHE and the attenuator loop didn't get activated for safety reasons (check the wiring & cables). If the light of amp 4 is off, the loop is deactivated.
Exit and save the System Menu by pressing the CTRL button again for 3 seconds, then releasing it. The CTRL turns red (or green if linked) and the switcher is back in normal switching operation. All settings are saved and will be automatically loaded on the next power-up.
Activate a speaker cab and an amplifier on the KHE. Slowly increase the volume of the amp and the attenuator and verify everything works as intended.
Notes:
The attenuator loop won't turn on if no actual attenuator is connected. The KHE checks the attenuator load resistance, and if it doesn't detect it, the attenuator loop stays inactive for safety (AMP 4 light blinks four times). It's crucial to connect the attenuator before activating the loop.
Turning off the KHE Attenuator Loop doesn't bypass the attenuator itself. The KHE does not have an Attenuator Bypass function. To fully deactivate the attenuator, both disconnect the attenuator cables at the S-Line jacks and disable it in the system menu. It's essential to always deactivate and disconnect the attenuator to prevent potential damage to the KHE, the amps, or the attenuator. If the Attenuator Loop is inactive, the S-Line jacks operate in Link Mode configuration for connecting KHE switchers.
When the KHE powers up, the attenuator loop is only activated if the KHE detects the presence of the attenuator. If the attenuator is not connected or in bypass mode, the attenuator loop remains disabled. All cab lights will blink if the attenuator is missing or in bypass state (new 2024 feature, serial nr B6-xxx or higher).
Therefore, if the attenuator has a BYPASS switch, it's important to set it to 'on/active' before turning on the KHE.
Learn more: ACS Attenuator Loop Guide
Troubleshooting & FAQ
No sound at all / Attenuator isn’t working correctly
Check if the Attenuator Loop is activated in the KHE System Menu.
Maybe it got deactivated because it not connected during power-up (safety feature)?Make sure an amp + cab is activated on the KHE
Double check wiring, it’s easy to mix things up.
Make sure cables are fully inserted & functional.
Downsize system to only amps+cabs with no attenuator or pedals.
Make sure the devices are being operated correctly.
Hum Noise or High-Pitched Squealing Feedback Noise
Is the KHE Attenuator Loop activated? Double-check everything above.
Dynamic Noise: Does the noise change your position in the room? Does it get worse if you move closer to the attenuator or load box? If the noise disappears when turning the guitar volume down, then the noise is most-likely caused by magnetic interference with the (reactive) load device and the guitar pickups. You are standing too close to the device. Move your guitar around to learn how it reacts. Try moving the attenuator or load box a little further away or lower gain and volume as a last resort.
Static Noise: If the noise is still present, even with the guitar volume turned all the way down and not changing with your position in the room, the noise is most-likely caused by a ground loop somewhere. First, check the pedals and the fx-loops. Make sure to use isolated 9V power for the fx-loop to avoid ground loop. Don’t use daisy-chain power adapter cables. Temporary remove the pedals to isolate the problem. If using a noise gate with key input such as the Fortin Zuul, use a splitter with transformer isolation for the key input to avoid ground loop. Keep the pre- and post pedal section ground isolated all the time. Experiment with the Ground Lift Switch settings. Make sure to have an amp activated on the KHE.
Sound or noise coming from inside amp/attenuator/load box
Sound of broken speaker inside the amp: When an amp or load box is pushed hard, it can cause weird noise and sound which kinda sounds like a small broken speaker, coming from inside of the amp or transformers. Fear not! This is normal. The vibrations from the transformer laminations and inductors can create strange distorted sounds, but there's nothing to worry about.
High-pitched squeal coming from inside the amp: Immediately power everything off (KHE, Amps) and verify the correct wiring of the amp. Make sure the cables are fully inserted and in good working shape.
Learn more: KHE Troubleshooting Guide and ACS Attenuator Loop Guide
Return Home: KHE ACS Help Center
Disclaimer: All product names, trademarks, and logos used in this guide belong to their respective owners. This guide is purely informational and does not suggest endorsement, sponsorship, or affiliation with the mentioned companies. While great efforts have been made to ensure accuracy, actual compatibility of our product with third-party products may vary, and we do not guarantee their performance or functionality. ALWAYS READ AND STUDY THE USER MANUALS OF THE INVOLVED PRODUCTS. Users are advised to thoroughly test and validate any combinations, and we disclaim responsibility for any issues that may arise. If you have any feedback to help improving this guide, please let us know.