What Is A Ground Loop Isolator And How Do They Work?

Hum or ground loop problems in your amplified audio system are incredibly annoying. Thankfully a ground loop isolator can help in many cases.

In this article, I’ll explain what you need to know:

• What exactly a ground loop isolator is and how they work.
• Why they’re necessary sometimes and the basics of noise in an audio system.
• How they can affect sound quality.
• Advice on what to look for when shopping for one.

This article is part of the audio installation accessories main page.

What is a ground loop isolator?

An audio ground loop isolator is a type of noise filter used to prevent electrical noise or hum, picked up by audio signal cables along the ground conductor path, from being amplified. They work with line level audio signals via RCA or 3.5mm connectors between a stereo, AV receiver, or car head unit RCA audio outputs and an amplifier that share a common ground for power.

Ground loop noise and hum also affect video systems, although in that case, the noise often appears as distortion in the video signal. 

Any time multiple audio devices are connected with cables there exists a potential for ground loops.

How does a ground loop isolator work?

Ground loop noise or hum is a common problem in many home stereo, auditorium, theater, or car stereo amplified systems due to having multiple paths with differing ground potential. When audio signal cables such as stereo cables with RCA plugs used between an audio source and an amplifier, small currents may create voltage potentials that can be picked up as noise.

The different grounding points have different resistance, which can mean return current flowing through them can develop a small electrical signal introduced in the audio devices being used.

The type of noise varies by the equipment and system in use:

• Car audio systems often have “alternator whine”, a high-pitched noise sound that varies with an engine’s speed while running.
• Audio equipment in home stereo, church, theater, and similar systems can have a 60Hz or 50Hz “hum” produced by the alternating current (AC) power source. AC power cycles the voltage polarity 50 or 60 times per second, depending on where you live.

Others can exist as well but these two are the most common. A loop has formed, which allows these noise signals to be picked up and carried by the signal conductor and/or the ground shield conductor of one or more cables.

An isolator eliminates ground loop noise by physically isolating the ground path signal cable conductors, disconnecting the different ground potential points, and preventing noise from being carried into the signal side of an amplifier to be heard from speakers. Most are easy to use by plugging the RCA connectors inline with RCA cables and then to the amplifier.

What is inside a ground loop isolator?

Most use a simple design of two electromagnetic transformers that carry the input signal to the output side while breaking the ground connection. The input signal is duplicated on the output side via magnetic fields created by the many copper wire windings wrapped around a metal core.

These windings induce an identical signal in a similar winding on the other side, duplicating the input signal without an electrical connection. A similar design is used in line level converters which also isolate their inputs and outputs.

Do ground loop noise isolators always work?

Unfortunately, they’re not always guaranteed to solve your ground noise issues. Your results can vary. Ground loop noise can be an extremely challenging and frustrating problem to solve.

However, in my experience, the majority of the time, they can eliminate or significantly reduce engine whine or AC hum. If an audio system has a very large amount of ground wire points or metal ground points they may not help. Those have an above-average ground loop problem difficulty.

I’ll cover some additional tips below that can help sometimes.

Do ground loop isolators affect sound quality?

Yes, commonly available ground loop isolators often have a poor frequency response that can hurt audio quality, especially in the bass (low-frequency) audio range. Based on my car stereo installation experience, I’ve seen many cases where a lack of bass response when a cheap ground loop breaker was used.

One reason is that cheaper models often use low-quality audio isolation transformer parts with poor performance across the 20 to 20kHz audio range. Some aren’t even designed for music signal use!

Higher-quality models typically use proprietary audio transformers designed to perform well with full range audio signals instead of general applications.

The brand and model you buy makes a HUGE difference!

What to look for when buying one with better sound quality

When shopping for a model that won’t hurt your system’s sound quality, you’ll want to look for that gives specific performance values, such as:

• The decibel (dB) deviation over the audio range is the amount the output will vary (plus or minus) from the input over the entire frequency range. The smaller the dB specified, the better.
• Frequency range specs such as “30 Hz to 20kHz” or similar.

Remember this rule of thumb: If the specifications aren’t provided, you can assume it’s probably not great. This is consistently the case based on what I’ve seen for many audio products of this type.

How much does a good quality ground loop noise isolator cost?

If you want very good audio performance, expect to spend around $45 and above for a quality ground loop breaker. Common, everyday units sold without specifications, while affordable (under $25) are nearly always very similar in quality.

Here are some recommended options:

• Massive Audio NOISE-OFF isolator (about $45) – Very good performance; while intended for car stereo use, it’s also capable of use with home stereo systems. Includes a small gain (signal boost) on the output signal side.
• ART Pro Audio DTI Dual Transformer/Isolator (about $79.99) – very flexible use for many applications, including balanced XLR cables and unbalanced RCA cables.
• Jensen CI-2RR Iso-Max Stereo Hum Eliminator (about $239.99) – pricy but high quality and includes shielded custom transformers. Good for as high as 40kHz, with an almost perfectly flat response up to nearly 20kHz.

Is it bad to use a ground loop isolator in audio?

While it’s not “bad” to use an isolator, it’s often not the preferred option when dealing with a ground loop issues for several reasons:

• Cheaper units can hurt sound quality and bass performance, so unless you can buy a good-performing unit, it’s a risk.
• The additional cost required and it’s one more item you’ll have to install.
• For audiophile-quality goals, it’s definitely not preferred as it introduces another item in the signal path.

Whenever possible, if you have the time, here are a few things that can sometimes avoid the need to use an isolator:

• To cut out hum, an AC power isolator transformer can help by physically disconnecting the ground and neutral AC power connections.
• When working with source units that only use a few amps, an isolated AC-DC or DC-DC power supply can help by breaking the ground loop before the audio connection. This avoids the need to affect the sound quality.
• Sometimes using small jumper wires (for example, speaker wire) can be used to “short” and fix a ground loop by jumpering different ground points. This can sometimes negate the noise-causing ground connection issues.
• Changing ground points or connecting a source unit and amplifier to the sound ground points.

When is a ground loop isolator recommended?

There are definitely times when it’s just not practical to avoid using a ground loop isolator or you simply can’t find another way to solve your noise problem. That being said, here are a few guidelines for when it’s more practical to use one:

• When doing paid audio installation work or when there’s not enough time to troubleshoot the ground loop. This is especially true for car audio or home stereo installation jobs.
• When you’re not experienced with troubleshooting or find it too difficult.
• In cases where you’re unable to swap out cables or electronics (this is pretty common when working on someone else’s system or when they cannot afford to pay labor costs it may take to resolve it otherwise.