Carvin BX250 & MB Series MicroBass Amplifiers USER MANUAL

Product Overview

The Carvin BX250 and MB Series MicroBass Amplifiers deliver classic natural bass tone with extensive tonal control and impressive headroom. The BX250 Head and Combo models provide 200W at 8 ohms and 250W at 4 ohms. They feature four discrete Class A input stages for harmonic richness, a boutique flat response preamp, and extensive tone shaping capabilities. The DRIVE control increases harmonic content as it's turned up. The amplifiers utilize a Class-D output stage and a lightweight switch-mode power supply, resulting in less energy consumption and heat generation. These amplifiers are built with a light weight, solid design, and bullet-proof construction for durability.

Key Features:

• Discrete CLASS A input stages
• Preamp DRIVE and MASTER volume controls
• 2 mid sweep semi-parametric EQ, BASS and TREBLE controls
• CONTOUR pre-shape control
• Single knob COMPRESSOR
• DIRECT OUT balanced XLR with LEVEL, PRE/POST and GROUND/LIFT switches
• MUTE switch for silent tuning or headphone practice
• TUNER/PHONES output jack (independent of MUTE switch)
• TWEETER DIM switch for controlling speaker brightness (on combo models)
• CLASS-D amplifier runs cool and consumes less power
• Solid metal shaft controls with panel-mounted threaded metal bushings
• MIL SPEC, double-sided, FR-4 glass epoxy circuit boards
• Energy efficient worldwide power supply (90-250VAC, 50-60Hz)
• Compact and lightweight design

Getting Started

1. With the POWER switch OFF, connect your instrument to the INPUT jack. For the BX250 head, also connect a speaker (4 ohms or higher) to a speaker out jack.
2. Set the DRIVE and MASTER volume controls to "0". Set the ACTIVE INPUT switch according to your bass type.
3. Set the four tone controls (BASS, TREBLE, LO MID, HI MID) to their center "0" position and the CONTOUR control to "FLAT". This is the amplifier's "FLAT" setting.
4. Turn the amplifier ON. Turn up the volume on your bass guitar. Gradually increase the MASTER control to your desired listening level. If no sound is heard, turn down the MASTER, check the MUTE switch, speaker connections, and the POWER (blue)/PROTECT (red) LED status.
5. Increasing the DRIVE control adds harmonic richness to your sound and also increases volume. Re-adjust the MASTER volume after adjusting the DRIVE.
6. Adjust the tone controls to your preference. Note that sometimes turning down a MID control can achieve a better sound than boosting others.
7. For more volume, consider adding an external speaker. Doubling your speakers increases acoustic output by a factor of four. Be mindful of speaker limits to avoid damage.

Explore the features and sounds of your BX/MB amp to realize its full potential.

Receiving Inspection

Inspect your unit for any damage that may have occurred during shipping. If damage is found, notify the shipping company and CARVIN immediately.

Save the original carton and all packing materials for potential future shipping. CARVIN and the shipping company are not liable for damage caused by improper packing.

Save your invoice, as it is required for warranty service.

If you find items missing, they may have been shipped separately. Allow several days for the rest of your order to arrive before inquiring.

Record the serial number on the enclosed warranty card for your records. Return your portion of the card with your name and comments to CARVIN.

USA customers can register online at: www.carvinaudio.com/pages/registration

Specifications

Front Panel Controls

Image of the Carvin BX250 Micro Bass amplifier front panel controls, showing numbered input jacks, switches, knobs, and indicators.

1. INPUT JACK

The 1/4" phone jack is a high impedance instrument input designed to handle both active and passive basses in connection with the ACTIVE switch.

2. JEWEL LIGHT

BLUE: POWER ON/SYSTEM NORMAL
RED: STARTUP/MUTE/COMP/PROTECT
The POWER switch turns on the amplifier. A BLUE light indicates the amp is ready. A RED light indicates startup sequence, MUTE engaged, COMPRESSOR active, or a PROTECT mode (e.g., shorted speaker output or impedance below minimum rating). If the power indicator turns OFF or stays solid RED, reset the amp by turning the POWER switch OFF for about 10 seconds, checking external speaker connections, and turning it back ON.

3. MUTE SWITCH

Turns off the signal to the amplifier and the DIRECT OUT. The JEWEL LIGHT turns RED when MUTE is active. Ideal for changing basses, silent tuning, or headphone-only practice. The TUNER/PHONES output is never muted.

4. ACTIVE SWITCH

Flip to the DOWN position for standard bass pickups. Flip to the UP position for basses with an onboard active preamp.

5. DI LEVEL (DIRECT OUT, PHONES)

Controls the output level of the XLR DIRECT OUT and the 1/4" PHONES/TUNER jack. This level is independent of the MASTER level. The PRE/POST switch determines if DRIVE, COMPRESSOR, and TONE controls affect this signal.

6. DRIVE CONTROL

Adjusts the input level to the CLASS A preamps. It serves two purposes: adjusting input sensitivity for different bass pickups and altering harmonic content. Turning the knob towards 10 creates a more overdriven tone. The DRIVE control also affects the amplifier's volume; use it in conjunction with the MASTER control for desired overall volume.

7. CONTOUR CONTROL

Provides a variable mid-range scoop. At "FLAT", there is no change to mid-range frequencies. Clockwise rotation scoops mid-range frequencies, with a maximum cut of -15dB at 500Hz (scoop centered at 350Hz).

8. BASS AND TREBLE TONE CONTROLS

Custom-shaped tone controls for punchy lows and crisp highs. Turning right boosts, turning left cuts the signal. BASS affects frequencies starting at 80Hz, TREBLE at 5kHz. Use with caution to avoid distortion or overpowering speakers.

9. SEMI-PARAMETRIC MID SWEEP TONE CONTROLS (LO MID, HI MID & FREQ)

These controls allow fine-tuning of the overall sound. The FREQ control's function is dependent on the GAIN setting. Experiment by adjusting the FREQ knob across its range while playing to hear how the added mids change frequency, and how GAIN affects this.

10. COMPRESSOR

Reduces the volume of the incoming signal as it reaches a preset maximum level. Turning the knob clockwise increases the "compression ratio" (from 1:1 at OFF to 3:1 at MAX). A compressor helps reduce peaks (transients) from playing, allowing for higher overall volume without distortion. The JEWEL LIGHT flashing RED indicates loud peaks being compressed.

11. MASTER VOLUME

Controls the overall volume of the amplifier. Reduce MASTER if the sound becomes overly distorted. The COMPRESSOR can also help prevent distortion or speaker overloading.

12. DIRECT OUTPUT XLR JACK (MUTED)

Provides a balanced, independent output straight from the input jack (PRE setting). The output level is controlled by the DI LEVEL. The MUTE function affects this output, allowing quiet tuning. The PRE/POST switch determines if DRIVE, TONE, and COMPRESSOR controls affect the DIRECT OUT signal. The XLR output is protected against phantom power.

13. DIRECT OUTPUT GROUND LIFT SWITCH

Use this switch (GND=out, LIFT=in on BX250 head) to lift the ground pin of the XLR connector to reduce hum when connecting to a mixer.

14. PRE/POST SWITCH

Affects the DIRECT OUT and PHONES/TUNER signals. "POST" includes DRIVE, COMPRESSOR, and TONE controls. "PRE" bypasses these controls. The DI LEVEL adjusts the level in both positions.

15. PHONES/TUNER JACK (UNMUTED)

Stereo 1/4" jack for connecting a tuner or headphones. Volume is controlled by the DI LEVEL. This output is unaffected by the MUTE function. To listen to headphones without hearing the main speakers, turn down the MASTER or engage the MUTE switch and adjust headphone volume with DI LEVEL. The PRE/POST switch affects this output.

16. TWEETER DIM SWITCH (MB COMBOS)

Allows attenuation of the internal tweeter to control speaker brightness. This switch does not affect speakers connected to the EXT SPEAKER jack.

17. SPEAKER OUTPUTS

Combo models (MB10, MB12, MB15) have one 1/4" extension speaker output parallel to the internal 8-ohm speaker. An additional speaker with an impedance greater than 8 ohms can be connected. The BX250 head has two 1/4" speaker outputs. The total impedance must not go below 4 ohms. Going below the minimum load may cause the amp to shut off or the JEWEL LIGHT to turn RED. To reset, turn off the POWER switch and connect the recommended load.

Speaker Combinations/Ohms:

• One 16 ohm speaker + one 8 ohm (MB spkr.) = 5.33 ohms (OK)
• One 8 ohm speaker + one 8 ohm (MB spkr.) = 4 ohms (OK)
• One 4 ohm speaker + one 8 ohm (MB spkr.) = 2.66 ohms (NO)
• Two 8 ohm speakers = 4 ohms (OK for BX250 head)

18. POWER SWITCH

Turns the amplifier ON or OFF. The JEWEL LIGHT will be RED for approximately 2-4 seconds during startup, then turn BLUE. If it remains RED, check the amp.

19. AC POWER JACK & FUSE

Accepts 90-250VAC, 50/60Hz. A detachable power cord is supplied. Use a grounded 3-prong power source. The internal fuse is a 250V Slow Blow rated at 5A. To check or replace the fuse, remove the power cord and the enclosure lid.

Rear Panel (BX250 Head)

Image of the Carvin BX250 Head rear panel, showing connections for DIRECT OUT, PHONES, TUNER, EXT SPKR, and AC POWER JACK.

• DIRECT OUT
• PHONES TUNER
• EXT SPKR
• LIFT POST / GND PRE (Ground Lift Switch)
• POWER ON/OFF Switch
• AC POWER JACK & FUSE

Combo Speaker Configurations

Illustrations of the Carvin BX MicroBass combo speaker configurations:

Helpful Hints

1. NO SOUND: Check if the MUTE function is engaged. Ensure speakers are properly connected.
2. NO HIGH FREQUENCIES: Check if the TWEETER DIM switch or HIGH FREQUENCY ATTENUATION control is set low or OFF. The HF driver may be damaged from excessive power or distortion.
3. AMP SEEMS VERY SENSITIVE TO INPUT SIGNALS: The DRIVE control might be turned all the way up. The ACTIVE switch may need to be engaged.
4. DIR XLR HUM: Try switching the rear GND LIFT switch IN or OUT. Check for noise from external effects or bad cabling.
5. POOR BASS FROM MULTIPLE ENCLOSURES: Ensure the external speaker is in phase with the internal speaker. Check wiring for correct phase, reversing (+/-) on the external cabinet if necessary.
6. FOR MAXIMUM OUTPUT: Use multiple speakers or enclosures. Doubling speakers increases acoustic output by a factor of four. Load the amplifier to its lowest minimum impedance for maximum RMS power. Exceeding the minimum load may cause the amp to shut off or enter "protect" mode. Reset by turning the amp off and connecting the recommended load.

The BX Microbass is a powerful amplifier. Ensure your speakers are suitable for the available wattage. Driving speakers with too much wattage can cause distortion and failure. If distorted sound occurs, reduce the volume.

Safety and Important Information

CAUTION: RISK OF ELECTRIC SHOCK. DO NOT OPEN. This symbol alerts the user to the presence of uninsulated "dangerous voltage" within the product's enclosure that may constitute a risk of electric shock.

This symbol alerts the user to the presence of important operating and maintenance instructions in the accompanying literature.

IMPORTANT! FOR YOUR PROTECTION, PLEASE READ THE FOLLOWING:

• WATER AND MOISTURE: Do not use near water. Prevent objects from falling and liquids from spilling into the enclosure through openings.
• POWER SOURCES: Connect only to the power supply type described in the instructions or marked on the appliance.
• GROUNDING OR POLARIZATION: Ensure grounding or polarization is not defeated.
• POWER CORD PROTECTION: Route cords to prevent them from being walked on or pinched, paying attention to plugs. The appliance inlet is the disconnect device and should be readily accessible.
• SERVICING: Do not attempt to service the appliance beyond instructions. Refer all other servicing to qualified personnel.
• FUSING: If equipped with a fuse receptacle, replace only with the same type fuse. Refer to unit markings for correct fuse type.

SAFETY INSTRUCTIONS (EUROPEAN)

AC power cord conductors are colored as follows: GREEN & YELLOW - Earth, BLUE - Neutral, BROWN - Live.

U.K. MAIN PLUG WARNING: A molded main plug cut from the cord is unsafe. NEVER insert a damaged or cut main plug into a power socket.

Limited Warranty

Carvin products are guaranteed against failure for 1 YEAR unless otherwise stated. Carvin will service and supply parts at no charge to the customer during the warranty period. Shipping costs are the customer's responsibility. CARVIN DOES NOT PAY FOR PARTS OR SERVICING OTHER THAN ITS OWN. A copy of the original invoice is required to verify warranty. Carvin is not responsible for horn drivers or speakers damaged by this unit. This warranty does not cover damage due to natural disasters, accidents, abuse, loss of parts, lack of reasonable care, incorrect use, or failure to follow instructions. This warranty is in lieu of all other warranties, expressed or implied. No representative is authorized to assume any liability for Carvin. CARVIN SHALL NOT BE LIABLE FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES.

Maintaining Your Equipment

Avoid spilling liquids or allowing foreign matter inside the unit. Clean the panel with a dry or slightly damp cloth. Avoid prolonged use in caustic environments (e.g., salt air) without adequate protection.

Service

In the USA, visit www.carvinaudio.com. Outside the USA, contact your dealer or visit www.carvinaudio.com and click on "Dealers" for your nearest service center. Include a written description of the problem, serial number, and date of purchase.