How To Drain Filter Caps On A Guitar Amp: Draining Filter Caps

So, what is a cap discharge? How do you discharge amp filter caps? How do I know if my filter cap is bad? Do filter caps affect tone? These are just some of the questions that always come out when it comes to filter caps in your guitar amplifiers. As musicians, it is always an advantage if we know many things about our gears, but you are not familiar, especially with the filter caps, then you are in the right place, as we are going to give light with some queries about filter caps.

So, what is a filter cap? A filter cap or also known by some as a filter capacitor, is a type of capacitor that can filter a specific range of frequencies or even a particular frequency from a circuit. It is able to filter unwanted frequencies and is also able to filter out signals with low frequency. In guitar terms, the filter capacitor filters out the noise after the rectifier stage.

How Do I Know If My Filter Cap Is Bad?

There are some signs that you can check whether the filter caps of your guitar amp are good or already bad. The first thing you will notice from your guitar amplifier is its humming. 

It is very normal to hear guitar amplifiers produce a very low-level 60-cycle hum that comes out to the speaker, but when you already hear the humming, even if you are already more than five feet away from the guitar amplifier, then you should already check or even replace the filter caps.

When it hums at 120 Hz, it is one of the usual indicators that the filter cap already needs to be replaced. Try to smack the guitar and wait if it produces rumbling sounds and strange noises; then you should also check it out. Another indicator you should look out for is when your guitar amp starts to sound like a 60-cycle growl; then, you should expect that you will have to change your filter cap in no time.

Another sign that the filter caps of your guitar amp are already bad is when it starts to produce a ghost tone over the fundamental note. It sounds similar to a ring modulation effect. This usually shows up when you strum the higher strings of the guitar.

You can also check out your guitar amp as if its low frequencies start to sound farty while the high frequencies lose their brightness and sparkles. If this happens, then you should already change the filter caps. Guitar amplifiers with filter cap issues lose their dimension as the harmonics are already incorrect, and the notes played do not develop similarly to their original state.

The last thing as an indicator for bad filter caps is if it starts to leak or dry out over time. When it comes to bad filter caps, it appears to bulge, and you can also see some leaking on them. If this happens, then you should already replace the filter caps. To physically see the bad filter caps, you should open up your guitar amplifier.

Filter caps on guitar amps usually have a lifespan of 15 to 20 years, but some last only for ten or even less, while some also reach up to 30 years and beyond. There is really no specific period on when to replace the filter caps on your guitar amplifier, so you must know all the symptoms of a bad filter cap, so you can immediately replace it.

Do Filter Caps Affect Tone?

If you are curious whether filter caps affect the tone of your guitar amplifier, the answer to that would be yes. Filter caps somewhat affects the tone of your guitar amplifier. As you already know, bad filter caps will make your guitar amplifier sound really bad and unnatural. Bad filter caps also produce loud humming, which is painful for the ears to listen to.

Newly replaced filter caps will make your guitar amp sound more punchy and clear than before. If you also increase the filtering values of the capacitors, this will usually result in a tightened-up tone, which has some focus on the low end, making it more punchy in the low frequencies. If you lessen the filtering values, it would also do the opposite tone.

Why Capacitors Need To Be Discharged?

Capacitors are known to store charges for a long time, especially if they do not have a bleeder resistor on them that gets rid of the electric charge when the electrical device is turned off. When you accidentally touch the capacitor, the stored charge can pass through your body, which can be dangerous.

When the energy stored in the capacitor goes through your body, you can feel some tingling, shock, or even burns, but the worst thing that can happen to you is that your heart can stop when the current passes through your body, which could kill you. This is why you should discharge capacitors if you are going to replace them or do anything on the electrical board.

How Do You Discharge Amp Filter Caps?

There are many ways that you can discharge the filter caps on your guitar amplifier, but you should never forget to be careful in discharging the filter caps, as it is a dangerous thing to do, especially if you do not have any idea what you are doing. Doing this thing without being safe could result in injuries or can even be fatal for the worst condition.

Safety first should always be your motto when doing any electrical-related work. So, to discharge the filter caps, these are things that you will need: a multimeter, a cable with two alligator clips on both ends, and a resistor, preferably with an impedance of equal to or more than 100 ohms.

The first thing you should do is disconnect the AC completely. Double-check if you have already properly disconnected it. Check again if the AC cord is already disconnected. This is just to ensure your safety before you can discharge the filter caps of the guitar amplifier. The next step is you take one of the ends of the cable with alligator clips and clip it to the amplifier’s chassis properly, as this will serve as its ground.

The next thing to do is to attach one end of the resistor to the other end of the cable with the free alligator clip. The next thing to do is to locate the positive terminals of the filter caps, and if you have found them, start to touch the positive terminals with the other end of the resistor that is not attached to the alligator clip. Do this for a few seconds, and make sure to repeat to discharge the filter caps surely.

The last thing to do before removing the filter caps on the guitar amplifier when replacing it is to check whether it still has some voltage in it using the multimeter. Once the voltage is discharged, you can see in your multimeter that the capacitor has only less than one or zero volts. The multimeter is really important so that you can safely check whether the filter caps have already discharged or not.

So, how to drain the filter caps of a guitar amp? Use a resistor that has equal to or more than 100 ohms to drain the stored energy from the filter caps. Always check if the filter caps have already drained before you replace them.

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