ACS Attenuator Guide

The KHE Amp Cab Switchers have an Attenuator Insert Loop. This is a serial insert point between the amp outputs and the speaker cabs, enabling to share a single attenuator globally with all connected amps and speaker cabs.

The ACS is compatible with all types of power attenuators: Boss Waza TAE, UA OX Box, Fryette Power Station, Two Notes Captor + Reload, Rivera Rock Crusher, THD Hot Plate and many more.

The Attenuator Loop is present at the white ACS S-Line Send and Return jacks. These jacks have two functions:

  • Link Mode: By default, the S-Line jacks operate in ‘Link Mode’, which is used to link or daisy-chain multiple ACS units with their speaker lines. In this mode, the S-Line Send & Return jacks are internally connected in parallel, both jacks have the same signal present.

  • Attenuator Loop: To use the S-Line jacks as an Attenuator Insert Loop, it must be activated in the ACS System Menu. This changes the internal connection of the S-Line jacks from parallel to serial, to insert a global attenuator between the amps and speaker cabs. By default, the Attenuator Insert Loop is deactivated. It must be activated in the System Menu for the attenuator to work correctly.

 

ACS 4x4FX Backpanel with the Attenuator Insert Loop

 
 

Attenuator Insert Loop

 
 


Wiring & Setup

With the ACS 8x4, ACS 4x4 or ACS 4x4FX, the attenuator is best connected to the white S-Line Send and Return jacks, which is the Attenuator Insert Loop. See some alternative connection variants for the ASX, CSX and ACS 4x2 at the end of this guide.

  1. Connect the ACS S-Line Send jack to the input of the attenuator by a speaker cable.

  2. Connect the ACS S-Line Return jack to the output of the attenuator by a speaker cable

  3. Activate the Attenuator Insert Loop in the System Menu (see below).

Activating the Attenuator Loop

  1. Connect the Attenuator to the white S-Line jacks and power-on the ACS as shown above. If the attenuator has a bypass switch, set it to active. Turn the volume of the attenuator all the way down as a safety precaution.

  2. Enter the System Menu by pressing the ACS CTRL button for 3 seconds, then release it.

    • The blinking interval of the CTRL light shows the active menu page. 1x blink = Page 1 - System Functions. 2x blink = Page 2 - MIDI Menu.

    • To switch the menu page, short-press the CTRL button. The attenuator loop control is on “Page 1 - System Functions”.

  3. Press Switch AMP 4 to activate the attenuator loop. If the light of amp 4 turns ON, the attenuator loop is activated.

    • The attenuator loop won’t turn on if no attenuator is connected. The ACS measures and checks the attenuator load. If no attenuator is detected, the loop won’t be activated, which is shown by 4 blinks to the amp 4 light. The attenuator must be connected first.

    • Deactivating the Attenuator Loop does not bypass the attenuator (learn more later in this guide),

  4. 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 ACS. Slowly increase the volume of the amp and the attenuator and verify everything works as intended.

 

The ACS System Menu Layout

 

ACS Attenuator Start-Up Check

On power-up, the ACS performs an automatic safety check: If the attenuator loop was previously activated, it will measure and check the S-Line jacks for a connected attenuator load. If the attenuator is detected by the ACS, it will enable the attenuator loop as normal (memory function). If no attenuator is detected however (maybe it got disconnected or set to bypass), the ACS will not enable the attenuator loop for safety reasons. The S-Line jacks will be internally connected in parallel instead of serial (link mode). A missing attenuator is shown by the blinking of all ACS cabinet lights (only for ACS units from Feb’24 or later with serial B6+). While the ACS cabinets lights are blinking, you can either a) re-connect the attenuator to allow the ACS to detect it and activate the loop or b) clear the error by pressing any switch. The Attenuator Loop will not be activated and the setting will be cleared.

Attenuator Operation Modes & Functions

Load Box or ‘Silent Mode’

Some attenuators can also function as a load box for silent recording. In this mode, the attenuator will present the full load for the amplifier, without a real speaker cabinet. The wiring and operation of the system depends on the attenuator model and intended use:

  • If the attenuator is used for both attenuation or silent recording (depending on the situation), connect the attenuator to the Attenuator Insert Loop (white S-Line Send & Return jacks). By default, the attenuator will work in attenuator mode as described above. To use it as a load box, it depends on the attenuator model:

    • Some attenuators have a variable speaker volume knob or control, such as the Boss Waza TAE or UA OX Box or many others. With these types, simply turn the speaker volume of the attenuator all the way down to zero, so there is no more sound from the speaker cab. On the ACS, a speaker output must still be active, but it won’t receive any signal from the attenuator (silent operation).

    • Some attenuators have a fix attenuation setting, such as the Two Notes Captor or XXX. Typically these attenuators have two operation modes: Load Box or Attenuator. The speaker output jack of the attenuator is usually a switching jack: If no cable is plugged in, the internal load box is active. If a cable is plugged in, it is in attenuator mode with the internal load deactivated, to use a real speaker cabinet instead. Thus, if this type of attenuator is connected to the ACS Attenuator Loop, it will function as an attenuator only. To use it as a load box, unplug the speaker output cable of the attenuator, so the internal load of the attenuator is active again. Make sure to unplug the cable on the attenuator side (switching jack). On the ACS, a speaker output must still be active, but it won’t receive any signal from the attenuator (silent operation). Be careful with this type of setup and check the attenuators user manual and verify a correct operation.

  • If the attenuator is used as a load box exclusively, without any real speaker cabinets in the setup, connect the attenuator to a red ACS Cabinet Output jack and use it like a normal speaker cabinet. There is no benefit in using the ACS Attenuator Loop in this type of setup.

Attenuator Bypass

  • Some attenuators have a bypass switch, such as the Fryette PS, Rivera Rock Crusher or Palmer PDI-06. This bypass switch can be used to remove the attenuator from the signal chain. Make sure to study the user manual of the attenuator and verify a correct operation. Make sure to always set the attenuator back to ACTIVE / ON before powering-on the ACS. The ACS checks on start-up if an attenuator is connected and would deactivate the loop if no attenuator load was detected.

  • If the attenuator does not have a bypass switch, the attenuator can not be bypassed. The ACS does not have an attenuator bypass function. Always disconnect the attenuator from the ACS S-Line jacks and deactivate the attenuator loop in the system menu. Deactivating the ACS Attenuator Loop alone does NOT bypass the attenuator - it must be disconnected too.

Attenuators with built-in FX-Loop

Some attenuators have a built-in fx-loop. This fx-loop can be used as a convenient master-fx-loop for all amps on the ACS. It also enables to use post-amp effects with amps that don’t have a real fx-loop. Learn more: KHE + Fryette Power Station and KHE + Boss Waza TAE



Attenuator with Line Out

Some attenuator have a line out jack. Typically this is a post-amp line output with the raw amp signal present. It can be used to record the dry amp signal at the same time, to be processed with IRs and such. Or it can be used as a amp-feed for the effects chain in a W/D/W setup or similar. In case of hum problems (ground loops), experiment with the ground lift switch settings of the devices. Check the attenuators manual for more info.


Things To Know



Attenuator Impedance

As always it is best to match the impedance of the amp to the impedance of the attenuator and speaker whenever possible. For example, if the attenuator is 8 ohm, set the amps and speaker cabs to 8 ohm. Ideally, the speaker cabinet load should be matched to the attenuator impedance as well. But in practice the speaker impedance is not that critical since the passive attenuator will provide the main load for the amp, so a speaker mismatch on the attenuator output side is usually safe. Make sure to check the attenuators user manual and verify a correct operation. Always match the amp impedance to the attenuator impedance. If it is an active attenuator, such as the Fryette PS, Boss TAE or Two Notes Reload, it will isolate the speaker cabs from the amp heads. Learn more: KHE Impedance Guide



Attenuator Power Rating

Make sure the attenuator has an appropriate power rating for the amp heads. Do not overload the attenuator or the ACS. Make sure to provide proper cooling airflow for the attenuator or load box. The ACS is designed to switch up to 150 Watts RMS. Do not run more than 150W RMS with the ACS. Learn more: ACS Maximum Power Rating



Attenuators with Combo Amps

Combo amps can only be used with a global attenuator if the combo power amp is fully connected to the ACS. If the combo is used with its internal speaker only, it is not connected to the attenuator. Learn more: ACS Combo Guide



Attenuators with Transistor Amps

Some attenuators or load boxes are not compatible with transistor- or solid-state amps. Make sure to check the user manual of the device and verify a correct operation. The ACS itself is fully compatible with any type of guitar amplifier - the attenuator is the limiting factor. Learn more: ACS Amp Types and Compatibility



Attenuator with built-in Tube Power Amp

Some attenuators have a built-in tube power amp, such as the Fryette Power Station. When using this type of attenuator with the ACS, always make sure to have one speaker cabinet output activated on the ACS to provide a safe load for the tube power amp of the attenuator. Use the ACS Recall Mode to automatically load the last active speaker cab on power-up. Use the new ACS Cab-Safe Mode to modify the ACS safety logic, so it is no longer possible to deactivate the speaker output at all. Learn more: KHE + Fryette Power Station



Attenuator 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 can happen 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. 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/OFF Sequence

  • Power ON: All amps + ACS + attenuator power OFF > ACS power ON > Attenuator power ON > Amp Heads power ON with standby for 2 minutes > ACS activate Amp+Cab > Ready to rock!

  • Power OFF: Deactivate ACS Amp+Cab > Amps power OFF > Attenuator power OFF > ACS power OFF > Good Night!


Blockdiagram

 

KHE ACS 4x4 Block Diagram

 



Safety Information

  • Use speaker cables for the attenuator input and output connection (1,5mm² or more). Use quality cables and make sure to fully insert the plugs into the jacks. Learn more: ACS Cable Guide

  • Always deactivate the amp and speaker cab on the ACS first before (dis-)connecting the attenuator.

  • The S-Line jacks have speaker level signal present. Do not connect any guitar pedals or effects to the S-Line jacks (risk of damage).

  • When disconnecting the attenuator, always first deactivate the Attenuator Loop in the ACS System Menu.

  • When disconnecting the attenuator, make sure to unplug the cables on the ACS as well (no floating cables).

  • NEVER deactivate the Attenuator Loop while keeping the attenuator connected. The ACS can not bypass the attenuator.

  • NEVER unplug the attenuator without deactivating the ACS Attenuator Loop. This would create a no-load scenario for the amp.


Alternative Connection Variants

Attenuator with ACS 4x2 or single Amps and Cabs

Instead of using the global Attenuator Loop, attenuators also can be connected directly to a single speaker cab or amplifier, to attenuate the volume of just one device. With the small ACS 4x2, which does not have the attenuator loop, these are the only connection variants.

  • With single speaker cabinets, connect the input of the attenuator to a red ACS Cabinet Output jack and connect the output of the attenuator to the speaker cabinet using speaker cables. With this configuration, the line out of the attenuator can be connected all the time to a recording interface or such.

  • With a single amplifier, connect the input of the attenuator to the amplifier speaker output and connect the output of the attenuator to the blue ACS Amplifier Output jack, using speaker cables. With this configuration, it is not recommended to connect the line out of the attenuator, to avoid hidden ground loops.

 
 

Attenuator with ASX 8 and CSX 8

  • With a linked ASX and CSX, connect the attenuator in between the units. On these units, the Attenuator Loop does not have to be activated in the System Menu - it is always active.

  • With a single ASX in Standalone Mode, connect the attenuator between the red Cabinet Output jack and the speaker cab.

  • With a single CSX in Standalone Mode, connect the attenuator between the amp output and the CSX blue input jack.

 

ACS 8x8 Setup with global Attenuator (ASX 8 + CSX 8)

 

Attenuator with linked ACS Switchers

With linked ACS switchers, it is possible to share a single attenuator globally with all switchers, amps and cabs. The wiring and setup depends on the switcher models being used. Learn more: Linking ACS Switchers (coming soon).

Attenuator Gear Examples

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.

Attenuator Bypass not working

Did you try to bypass the attenuator by deactivating the KHE Attenuator Loop, and have the attenuator still connected to the KHE S-Line jacks? This ain’t gonna work. The KHE can not bypass the attenuator. It must be disconnected and the attenuator loop must be deactivated. Make sure to rad the ACS Attenuator Loop Guide

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 lamminations 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

FAQ: Can I connect a effect pedal or preamp to the S-Line jacks?

Absolutely no. The S-Line jacks are speaker-level. Line-level devices would be damaged immediately.

FAQ: Can I use a load box in the Attenuator Insert Loop?

Yes this is possible. However, load boxes are usually best connected to a red cabinet jack, to use it like a normal speaker cabinet but for silent recording. If an load box, such as the Suhr Reactive Load, is connected to attenuator loop, the internal load will most likely be deactivated by its speaker output/thru jack (switching jack). So it only functions as an amp-tap (line out) for recording, w/d/w setups or similar. Check the user manual of the device and ensure correct use and operation.

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.