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.

What is a ground loop isolator?

how a ground loop isolator works diagram

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?

inside a ground loop isolator illustrated

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.

Note that alternator whine noise (engine whine) tends to be made up of frequencies in the midrange region of the 20 to 20 kiloHertz audio range. 60Hz or 50Hz hum is a very low pitch frequency in the bass region. Therefore, it sounds like a deep tone.

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

Do ground loop isolators affect sound quality?

ground loop isolator audio quality comparison

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

ground loop isolator quality specifications example

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?

ground loop isolator quality options examples

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?

is it bad to use ground loop isolator 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.
Marty

About the author

Marty is an experienced electrical, electronics, and embedded firmware design engineer passionate about audio and DIY. He worked professionally as an MECP-certified mobile installer for years before moving into the engineering field. Read more »

Your comments are welcome.
  1. Hi
    I have an Android head unit connected to 4 door speakers (coaxial) via factory fitted harness, all coupler to coupler fitting. On engine running there is low humming/static in speakers which increases with rpm. It becomes less audible if volume is increased. There is no humming, if I mute volume or turn the engine off. The headunit is made of plastic so not sure about grounding. The is no amp in the setup. Please help

    Reply
    • Hi Raj it sounds like you have a ground loop problem. You can try grounding the head unit in different locations to see if it improves. However, this type of problem is very frustrating and hard to resolve sometimes.

      I suspect it’s partly due to the head unit’s design.

      If you have an amplifier you can also try powering the speakers with that, then use a good quality ground loop isolator between the head unit’s RCA outputs and the amplifier’s inputs. I wish you the best of luck as it’s a very challenging problem sometimes.

      Reply
  2. I am not sure if what I have is ground loop noise or something that is inherent to my amplifier that I have. I have a Yamaha AV receiver. The main left and right preamp outs are going to a Carver M1.5t amp to run my front left and right speakers. When the system is up and running, I can hear a very faint hum/buzz from the speaker, mostly from the tweeter, so it is a high frequency.

    I do have to be right next to the speaker to hear it. I am thinking it is a harmonic of the AC or, possibly noise from the amplifier’s power supply. I have had the amp completely overhauled recently. All the electrolytic capacitors were replaced, and other critical components were replaced, and the amp tested to the factory specifications.

    The Carver’s power supply is unique in its design, so it is not like a typical amplifier’s linear power supply. It may be the noise from the triac firing and inducing the noise. One thing to note, is that the noise does not get louder as I turn up the volume. I also had a different amp in place at one point in this system, and I did not have any noise like I do with the Carver. If the inputs to the amp are disconnected, the noise gets a lot worse.

    What I am worried about is that I install one of the noise isolators, and it won’t solve the issue. The next test I am going to conduct is using an audio source, like my Samsung tablet, and connect it to my amp and make sure that no other devices are connected to the outlets on that circuit and listen for any noise.

    Reply
    • Hi Eric. Yes it sounds like perhaps it’s noise generated harmonically and carried or something else similar, just going by what you wrote. Unfortunately noise from power supplies is notoriously hard to resolve as it rides on top of the power supply rail voltage (pos. and negative supply voltages) and can appear at the output. Or gets carried along the ground connection.

      Unfortunately noise often simply requires trial and error. As the Samsung tablet is battery powered, im 95% confident you won’t hear noise with it (unless it’s plugged into a charger. You may need to buy a decent quality isolator for test purposes…ideally opening it in such a way you can return it if it doesn’t work out.

      Best of luck with it! I know how frustrating noise like that is with audio stuff!

      Reply
  3. What is the best noise suppressor/isolator would you recommend for recording music into interface?
    It is impossible for me to record an electric guitar: i have to rotate away from computer/interface to a very limited spot and hold a guitar in uncomfortable position, and a slightest move produces the noise. The interface is good, all updated, the gains are normal (or even lower than needed) – it is obviously “around”.

    Also, is there any way to lower the noise of amplifier (the noise itself, even if the guitar is not connected to it…Boss Katana)?

    Hoping for your clear and prompt answers and thanking you in advance….

    Reply
    • Hello Denis. There’s some information missing in your post but I’ll try to help anyhow. I’d need to know:
      • What interfaces you’re using for the music signal to the recording device/input.
      • How everything is powered and whether or not they’re powered from the same thing/source/outlet etc.
      • What type of noise you’re experiencing.

      If it is the standard 60 or 50Hz electrical hum, then a good quality ground loop isolator can solve it in many cases. However, if you’re not using RCA connectors you’ll need to get one that works with whatever interface you’re using (XLR, etc.)

      If you lower the gain of an amplifier then generally the noise is lower, but you have to increase the source signal level to compensate for the drop in volume (not always practical or possible).

      You can also try power everything from the same power source or outlet. Ground loops are a real headache and can take time to resolve which is one reason using an isolator is preferred by most people.

      Best regards.

      Reply
      • ~ The same day response – Thank you, Marty!

        You asked many questions and i can’t write short, so here we go…

        [EDITED FOR LENGTH]

        It is hard to tell (at least for me), what type is best in my case, where the quality of noise suppressors/filters begins or where just big prices begin. So i took a chance asking you. I hope your professional expertise will help t point out at specific products/choices.

        Thank you again, Marty!

        Reply
  4. Corrections:
    * edgy – not edge;
    * it is one of the best in low noise statistics, but i was getting lots noise and hiss badly over-powering the guitar sound when turning the knob of monitor mix to “instrument” (while recording) – wrongly placed additional insert.

    Reply
    • Hello Denis. As your prior comment was very lengthy I just saved the text and edited the comment for length.

      I’ll reply to your email address directly. Best regards. :)

      Reply
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