Imagine if our amps could talk- there would be a lot less incidents of blown speakers and mismatched impedances! While no one- even the most experienced guitar techs- can immediately determine exactly what caused an amplifier to fail without taking a look under the hood, some units do give off warning signs that there is something wrong to prevent that costly replacement or trip to the repair shop. Naturally, if you are really familiar with your amp, then chances are you know when it’s being pushed past its limits or set up incorrectly. But what happens if one day you’re not paying close enough attention or using a different setup? Today, we are going to discuss an overlooked, unsung hero of your amp- the protect light. Chances are you know it’s there, but you may have never seen it come on, or you have and you’re wondering what it’s trying to tell you.
An amplifier with a built-in protection circuit will have a protect light. It may be the same light as the jewel light, or a separate light altogether. It may or may not be the same color as the power light- there are many variations, so refer to your unit’s documentation if you are unsure where the protection light is or if there is a protection circuit. Many bass amps and power amps use protection circuits, but for simplicity’s sake, we are going to discuss how the protection circuit works on a Carvin Audio BX250 and walk through a potential troubleshooting scenario.
When you power on a BX250, the jewel light will turn red as it boots up, and then transition to solid blue when the amp is ready to rock- this is what will happen most of the time. However, there are a few circumstances that will cause the light to turn a solid red and stay that way, which indicates that the unit is going into protection mode. One of the most common causes is an impedance mismatch- that is, the BX250 is loaded below its minimum impedance rating (for more on this topic, check out this article). Immediately power off your amplifier and check the impedance rating of the cabinets you are using. Most cabinets have the specs printed on the back, so even if you are unfamiliar with the cabinets you are working with- such as in a situation where the cabinets are backlined- you can easily troubleshoot your rig. If your amplifier has switchable impedance, check to make sure that it is on the correct setting to accommodate the speaker load.
Another thing that may cause the red protect light to stay on is shorted or faulty speaker outputs. This may be caused by a wire’s insulation breaking down or connecting a head to a cabinet after it has already powered on. In instances like this, the protection circuit will kick in to protect the amplifier’s power supply.
While troubleshooting an amplifier in protection mode, make sure that the mute switch is not turned on, as this will also cause the jewel light to remain a solid red. The BX250 and many other amplifiers use the same solid red light to indicate both that the signal is muted and that the amp is in protection mode.
If your unit goes into protection mode, it is a good and bad thing- good that further damage is being prevented, but bad in that it may delay the gig. Knowing the possible problems that a protect light indicates is essential. If that red light comes on, stay calm, power off your amp, and check your speaker connections and impedance ratings, making any necessary adjustments. After ten seconds of being powered off, the amp is reset, so turn it on and watch for the protection light again.
An amp with a protect light can be a real gig saver. Has your amplifier’s protection circuit ever kicked in, and if so, what was the problem? Let us know in the comments!