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Is Your Preamp Broken? 11 Ways To Find Out

You’ve taken your amplifier and speakers out of the boxes, plugged it into the appropriate outlet, and all you get is a humming sound (or silence). How do you know if your preamp is broken?

Here are 11 ways to know if your preamp isn’t working:

  1. Check for a blown fuse.
  2. Try plugging the preamp into another outlet.
  3. Check if the power supply is working.
  4. Test the input and output connections.
  5. Try using another amplifier or speaker setup.
  6. Swap cables with another set.
  7. Replace any old capacitors.
  8. Check for dust and other debris.
  9. Check for defective diodes.
  10. Check for faulty transistors.
  11. Call a professional technician.

The rest of this article will explain each of these measures in detail. Read on for details on these and helpful preamp care and maintenance tips.


1. Check for a Blown Fuse

Preamplifiers usually come equipped with a fuse at the amplifier’s back that protects its components from damage due to power surges and other electrical problems.

Therefore, a blown fuse is a dead giveaway that there is a power issue with your preamplifier. A blown fuse means there is a current overload on the preamplifier. This can happen from a power surge or a short-circuited cable.

It is important to replace the broken fuse as soon as possible.

You can check whether or not your preamplifier has blown by replacing the fuse with a new one and turning the system on. If there is no current overload, the preamp will work again.

However, if the preamp doesn’t work, chances are that a different component is damaged.

2. Try Plugging the Preamp Into Another Outlet

If your amplifier is plugged into one specific outlet, try moving it to another, if possible.

If it still does not power on, you might have a wiring issue in the preamplifier. In this case, you will need to open up the preamplifier and inspect its wiring for any damages or loose connections.

3. Check if the Power Supply Is Working

There are two ways to check whether the power supply is in the right condition:

Way Number 1

You can quickly test if the preamplifier is receiving power by plugging any household electrical equipment into the same outlet as your amplifier and turning it on. If the electrical equipment is working properly, there is a power issue with your preamplifier.

Way Number 2

You can also use a multimeter to test the continuity of the power supply cables. 

Here’s how: Turn off the preamplifier and remove all its inputs and outputs from their sockets.

  1. Set the multimeter’s mode to DC voltage and connect each test probe to its corresponding power supply input or output socket.
  2. Plug in the preamplifier into an outlet and turn it on.
  3. Turn up the multimeter’s scale to a higher setting such as 50V or 100V and test the continuity of each power supply cable.

If there is no current flowing through any power supply cable, there is a fault in the preamplifier’s power supply. And you need to open up your preamplifier and check its wiring and components.

Note: If you need a reliable multimeter, I recommend this AstroAI Digital Multimeter from It’s versatile and features an anti-burn fuse that guarantees long life.

4. Test the Input and Output Connections

Damaged input and output connections can cause power loss in your preamplifier, resulting in it not powering on.

To test this, unplug all the inputs and outputs from their sockets and turn off the preamplifier.

Test the continuity of each input connection by plugging them back into their corresponding socket one by one.

Also, test if there is continuity between each output connection with its corresponding speaker or equipment’s socket. If you don’t get any current reading at either point, there is a fault in that specific input or output circuit.

5. Try Using Another Amplifier or Speaker Setup

If your preamplifier is not powering on, it’s best to try another amplifier or speaker set up to rule out faulty components. 

If the other amplifier powers up without any issues, it is likely that your preamplifier is faulty and needs replacement.

6. Swap Cables With Another Set

One of the most common reasons for your preamplifier not powering up is faulty inputs or outputs. If you can get your amplifier working with another speaker or equipment, you probably have a fault in one of the input or output circuits in your preamplifier.

You can quickly test this by swapping cables with another set. If the problem persists, try replacing them with new ones.

Most cable sets come with connectors that you can easily plug into each circuit board’s input and output sockets without any soldering.

7. Replace Any Old Capacitors

If your preamplifier is several years old, it’s best to replace any old capacitors as they tend to lose their charges over time and may cause power loss in your amplifier.

You can either ask a professional technician to do this for you or follow the steps below:

  1. First, turn off your preamplifier and remove its cover by unscrewing the screws holding it down.
  2. Use a PCB pencil or screwdriver to disconnect all the cables attached to circuit boards inside the amplifier.
  3. Once everything is disconnected, remove each capacitor carefully from the circuit board, noting they are connected. The markings on the capacitor will indicate the presence of + (positive) and – (negative) sides.
  4. Finally, check each capacitor on your replacement set to ensure it has the same specs as your previous ones before inserting them back into their corresponding sockets on the circuit board.

8. Check for Dust and Other Debris

The dust and debris build-up in preamplifiers can cause short circuit damage to the components, resulting in permanent loss of power.

Besides, dust will also shorten the life of your amplifier’s components, so it’s best to open up your preamplifier and get rid of any dust or debris that may be present.

You can clean the preamplifier parts with a cloth dampened in a mixture of distilled water and isopropyl alcohol. You should carefully rub the cloth over plastic, metal, and circuit board surfaces to remove any dirt or debris that may have accumulated.

Do not use excessive pressure when rubbing the surface. Doing so can damage your preamp’s components.

Note: Make sure you wear protective gloves while performing this task to prevent your hands from coming into contact with any chemicals used in cleaning your preamplifier unit.

9. Check for Defective Diodes

Although rare, you can check for defective diodes in older amplifiers using an Ohm meter. This test will help you identify if one of the power stages has malfunctioned, resulting in loss of power when turned on.

To do this, follow these steps carefully:

  1. Turn off your preamp and unplug all the cables connected to its circuit boards inside the amplifier along with attached speaker connections.
  2. Using a screwdriver, open up the amplifier and remove all of its circuit boards from its casing.
  3. Once you have all the boards in hand, turn them over so that their components face downwards.
  4. Next, attach an Ohm meter to a diode’s connection terminals on one board while touching it separately with your other hand. It would help to confirm how many ohms your amps diode should produce so that you can tell if it is faulty and needs replacement.
  5. Repeat these steps for every single power stage present in your preamplifier unit until you identify which power stages are giving out incorrect readings indicating there may be a problem with some of their diodes.

10. Check for Faulty Transistors

A transistor is a semiconductor that can either act as an amplifier or a switch, depending on how it is wired to other components in your preamplifier.

If any of the transistors inside your power stages are faulty, it will result in loss of power when turned on. You can check for shorted transistors using an Ohm meter.

To do this, you need to follow these steps carefully:

  1. Turn off your preamplifier and unplug all the cables attached to its circuit boards along with speaker connections inside the amplifier.
  2. Take each board out of its case and turn them over so that their components face downwards.
  3. Attach the ohmmeter lead to one of the transistors and touch the other one to it with your hand.
  4. Repeat this step for every transistor present in your amplifier until you identify which ones are giving out incorrect readings indicating that they may be faulty and need replacement.

11. Call a Professional Technician

If you still can’t power up your preamplifier, seek assistance from an experienced audiophile or sound engineer to do further tests on your amplifier and fix potential issues. 

Preamp Care and Maintenance Tips

Now that you know how to find out if your preamplifier is broken, here are some tips you can keep in mind when caring for and maintaining your audio equipment:

Keep Dust Away From Your Preamplifier

Never let dust accumulate on any of your audio equipment, especially your preamplifier. It will cause serious damage to the circuits inside. Overheating is also possible and may result in permanent power loss for your amplifier.

To avoid this problem, buy an anti-static brush or use a vacuum cleaner to carefully suck up any dust build-ups on the surface of your amplifier without causing any physical damage to the components inside it.

Keep Liquids Away From Your Preamplifier

Liquid spills can also lead to permanent damage to electronic devices like amplifiers.

Specifically, when liquids come in contact with capacitors or other electrical components, they can cause short-circuits, resulting in power loss for your amplifier.

To avoid this problem, make sure you don’t drink or eat near any of your audio equipment.

Turn Off Your Preamplifier After Use

To keep your amplifier safe from any damage due to overheating, it’s best to turn off all equipment (including amplifiers) after use and leave them turned off overnight before switching them back on again the next day.

This will allow circuits inside your amplifier to cool down before turning them back on and reduce the likelihood of any problems developing.

Related article: Should Amplifiers Be Left On? Here are the facts!

Don’t Expose Your Equipment to Extreme Temperatures

Temperature fluctuations can also affect power output in an amplifier and cause it to shut down unexpectedly.

Avoid placing your preamplifier near hot air vents or heating systems as these can raise its internal temperature too high, which may lead to permanent damage to your equipment.

Take Good Care of Your Cables

Remember, if you are using an interconnect cable between your amplifier and speakers, ensure that both devices’ connectors are properly connected before powering them on to avoid damage caused by short circuits.

Also, switch off both devices when disconnecting or connecting any cables to avoid a power surge.

Keep Your Cables Away From Electromagnetic Interference

Electromagnetic interference can also affect power output in an amplifier and cause it to shut down unexpectedly.

Make sure you place any amplifiers at least 10 cm away from electronic items like speakers, TV sets, or computers which can interfere with their normal operation and cause problems such as reduced sound quality or power loss.

Buy Quality Cables

Always buy quality cables to connect your audio equipment. Doing so can help reduce interference experienced during playback of music or other sounds and improve your system’s output quality.

This also means that you should never buy cheap imitations or poor-quality products, which will not only fail to deliver the pre-amplified signal correctly but may also cause irreparable damage to amplifiers after a few uses.

So make sure you look for high-quality brands like AudioQuest, Hosa, or QED when buying any cable for your amplifiers and speakers.

It’s always best to play safe than sorry!

Replace Faulty Capacitors

Capacitors are found inside your preamplifier and help store energy before powering on components in amplifier circuits.

If these capacitors wear out or stop working because of age, they lead to unexpected power failure in your amplifier, which may ultimately lead to permanent damage.

So if your preamplifier shuts down unexpectedly, one of the first things you will have to do is check if any capacitors are faulty by replacing them beforehand.

You can contact a professional technician in this regard or ask around for help from anyone with experience dealing with audio equipment.

Don’t Over Tighten the Screws and Knobs

The screws and knobs on all of your equipment should be properly tightened before use, but avoid over-tightening them as it can damage the equipment’s casing.

Also, never put too much force on the knobs as it can lead to scratches that are hard to remove later on.

On that note, just take good care of your audio system, and it will serve you well for many years!

In a nutshell, there are several things you should keep in mind to make sure that your home audio system is safe and running at maximum efficiency all the time.

As I’ve mentioned, taking good care of your amplifier and using good quality cables can also ensure that you get the best sound quality through your system setup.

In addition, you should also avoid over-tightening your amplifier knobs or screws as this can damage its casing and cause problems in proper functioning. If you’re still experiencing problems with your audio equipment, don’t hesitate to contact a professional technician immediately.

Final Thoughts

If your preamp is not working, then you should follow the steps outlined in this article to see if you can fix it. 

You may also need a professional technician’s opinion on what could have caused the problem and how best to fix it. That said, it would help to take good care of your preamp by following the mentioned guidelines.