The MESA/Boogie POWERHOUSE® Reactive Load Attenuator is a versatile device designed to allow guitarists to achieve the desirable tone, feel, and excitement of a tube amplifier running in its optimal power band, even at reduced volumes. It addresses the common challenge of maintaining a great tube amp sound in environments where high volumes are not feasible or tolerated.

Function Description:

At its core, the POWERHOUSE® is a reactive load attenuator. This means it provides a load to your amplifier's output section that mimics the impedance and response curve of a real speaker cabinet. This reactive load is crucial for protecting your amplifier's output transformer, especially when no physical speaker cabinet is connected, allowing for silent operation or significantly reduced volume levels.

The device offers several key functionalities:

Attenuation: It allows for the reduction of your amplifier's output volume without sacrificing the tone and feel derived from driving the power tubes. This is achieved through a 5-position rotary switch offering attenuation levels of 0dB (Bypass), -4dB, -8dB, -12dB, and -16dB.
Silent Recording/Practice: When the SPEAKER/LOAD switch is set to LOAD, the internal reactive load is engaged, enabling silent operation. In this mode, a line-level signal can be taken from the LINE OUT (DRY) output on the rear panel and fed to external gear such as Impulse Response (IR) players, additional amplifiers for re-amping, or effects processors. This signal is unprocessed and does not include cabinet simulation.
Live Monitoring with Attenuation: When the SPEAKER/LOAD switch is set to SPEAKER, the attenuator is active, and the signal is forwarded to your live speaker cabinet(s) connected to the TO LIVE SPKR CAB jacks on the rear panel. This allows you to drive your amplifier hard for optimal tone while controlling the overall stage or room volume.
Voicing Options: A 3-position mini toggle switch on the front panel provides voicing options: WARM (fuller sound), BRIGHT (more top end), and NORMAL (neutral response). This allows for fine-tuning the attenuated sound to suit different preferences or musical contexts.

Important Technical Specifications:

Power Handling: The POWERHOUSE® can handle amplifiers up to 150 Watts.
Impedance Versions: It is available in 4, 8, and 16 Ohm impedance versions/ratings, ensuring compatibility with a wide range of amplifiers. It is crucial to match the POWERHOUSE®'s impedance to your amplifier's output impedance.
Attenuation Levels:
- 0dB (Bypass)
- -4dB
- -8dB
- -12dB
- -16dB (with an additional LEVEL control for infinite attenuation)
Connections (Rear Panel):
- INPUT - FROM AMP SPKR OUT (1/4" jack): Connects to the amplifier's speaker output.
- LINE OUT (DRY) (1/4" output): Sends a line-level signal to outboard gear. The level of this output is controlled by a dedicated rotary knob on the rear panel and is unaffected by the front panel ATTENUATION controls.
- OUTPUTS - TO LIVE SPKR CAB (Two 1/4" jacks): Provides attenuated signal to live speaker cabinet(s). These jacks are wired in parallel.

Usage Features:

Reactive Load Technology: The core feature is the reactive load, which mimics a real speaker cabinet's impedance and response, preserving the amplifier's tone and feel even at low volumes or in silent operation.
Infinite Attenuation (LEVEL control): The -16dB attenuation setting is augmented by a LEVEL control, allowing for fine-tuning of the listening level down to whisper-soft volumes or even "INFINITE" attenuation (no sound). This is particularly useful for silent practice or recording.
Parallel Speaker Outputs: The two TO LIVE SPKR CAB jacks are wired in parallel, simplifying the connection of multiple speaker cabinets while ensuring proper impedance matching (users must calculate combined impedance).
Line Out Level Control: A dedicated rotary control for the LINE OUT (DRY) allows users to adjust the output level to match the input requirements of various external devices. It is recommended to start with this control fully counterclockwise and gradually increase the level.
Voicing Switch: The WARM/BRIGHT/NORMAL toggle provides quick and easy tonal adjustments to suit different musical styles or preferences.
Safety Precautions: The manual emphasizes the importance of setting the SPEAKER/LOAD switch correctly to prevent damage to the amplifier, especially when no speaker cabinet is connected. It also advises against running the amplifier's master volume all the way up when using the attenuator to prevent undue stress on tubes and excessive heat generation.

Maintenance Features:

Cooling Fan: The unit incorporates an internal cooling fan that is powered by the amplifier's speaker signal voltage. Its operation is dynamic, meaning it spins faster with louder signals and may only run during dynamic passages at lower volumes. This fan is crucial for cooling the internal load, especially during high-volume operation.
Ventilation: Users are advised to ensure adequate clearance on either side of the unit to allow for proper cooling and ventilation, which is essential for the longevity of the device and the internal components.
Cleaning: The manual specifies cleaning the apparatus only with a dry cloth.

The POWERHOUSE® is presented as a valuable tool for guitarists seeking to maximize their tube amplifier's potential in various scenarios, from silent recording and practice to live performance with controlled volume, all while preserving the authentic tube tone and feel.

MESA ENGINEERING POWERHOUSE - Page 4