ART CleanBOX II Two-Channel Hum Eliminator

The ART CleanBOX II is a passive two-channel hum eliminator that removes ground loop hum between pieces of audio gear, made for home studios, live rigs, installers and anyone hearing a constant buzz from speakers, mixers, synths or effects. It sits in the signal path between two devices, and its isolation transformers break the ground connection that causes the noise, while the audio passes through.

What causes ground loop hum?

A ground loop happens when two pieces of equipment are connected by an audio cable and also earthed through their own power cables, often at different points. The ground wire then carries a small current, and that current turns up in the audio as a low hum at mains frequency and its harmonics, sometimes with a buzz on top. It typically appears when you connect a computer to a mixer or studio monitors, add an outboard effect to a mixer’s send and return, or connect a synth or guitar processor to a PA.

The giveaway is a hum that stays constant whatever you play, and often changes or disappears when you unplug one audio cable.

How the CleanBOX II fixes it

Each channel has an isolation transformer. Audio passes across it magnetically, but there’s no direct electrical connection between input and output grounds. That breaks the loop at the audio cable, so the hum has no path to follow, while both devices stay safely earthed at the wall.

Because it’s passive, there’s nothing to power and nothing to switch on. Patch it in and the hum should drop away.

Two channels, flexible connections

The CleanBOX II has two 1/4″ TRS inputs and two 1/4″ TRS outputs, and each jack works with balanced or unbalanced signals. Use both channels for a stereo signal, such as a computer feeding a pair of monitors, or treat them as two separate mono lines, such as a reverb send and a delay send. The two channels are fully independent.

Audio performance

ART specifies a frequency response of 10 Hz to 50 kHz (±0.5 dB at +4 dBu), and low distortion: 0.01% THD typical at 1 kHz and +18 dBu, and under 0.05% at 100 Hz and +24 dBu. Insertion loss depends on what the output feeds. Into a typical high-impedance line input (100 kΩ), you lose only 0.4 dB. Into an old-style 600 Ω input, the loss is 5.5 dB, so you may need to turn up the gain at the receiving end.

Common setups

• Computer to monitors or mixer: place the CleanBOX II between the computer or audio interface outputs and your speakers, to stop hum and USB whine caused by a ground loop.
• Effects loops: put it on the send or return between a mixer and an outboard reverb or delay.
• Synths and drum machines: isolate a keyboard’s line outputs before they reach the mixer.
• Guitar processors into a PA or second amp: break the loop between two separately powered systems.

Who is the ART CleanBOX II for?

• Home and project studios with a computer, interface and monitors on different power points.
• Live and DJ rigs that connect gear powered from different outlets on stage.
• Installers connecting background music sources to existing amplifiers.
• Synth and outboard users with several separately powered devices in one setup.

It isn’t a fix for every noise. If the hum comes from a faulty cable, a dimmer, a pickup near a transformer or a bad earth in the building, isolation won’t remove it. It’s designed for line-level signals, so for turning an instrument into a balanced mic-level signal, a DI box with a ground lift is the better tool.

CleanBOX II vs a DI box with ground lift

Both use transformers and both can break ground loops, but they do different jobs. A DI box converts one unbalanced instrument signal into a balanced, low-level XLR output for a mixer’s mic input. The CleanBOX II keeps line-level signals at line level, on 1/4″ jacks, across two channels. For hum between a computer and speakers, or between a mixer and an effects unit, the CleanBOX II is the more direct fix. For more isolation options, see our signal splitters and isolation range.

Never cut the mains earth

Some people try to stop ground loop hum by removing or bypassing the earth pin on a power cable. Don’t. It removes a safety protection and can make equipment dangerous. Breaking the loop on the audio side with an isolator like the CleanBOX II keeps every device properly earthed.

Key features

• Two-channel passive hum eliminator
• Isolation transformer on each channel
• 2 x 1/4″ TRS inputs, 2 x 1/4″ TRS outputs
• Balanced or unbalanced operation
• No power required
• 10 Hz to 50 kHz frequency response
• Low distortion: 0.01% THD typical
• 0.4 dB insertion loss into 100 kΩ
• Compact, 408 g

Frequently asked questions

Does the ART CleanBOX II need power?

No. It’s fully passive and uses transformers, so there’s no power supply or battery.

Will it remove hum between my computer and studio monitors?

If the hum is caused by a ground loop, yes, that’s one of its most common uses. Place it between the interface or computer outputs and the monitors.

Does it work with balanced and unbalanced cables?

Yes. The 1/4″ TRS jacks work with both balanced and unbalanced signals.

Will it reduce my signal level?

Barely, with modern gear. The loss is 0.4 dB into a 100 kΩ input. Older 600 Ω inputs lose 5.5 dB, which you can make up with a little more gain.

Can I use one CleanBOX II for stereo?

Yes. It has two channels, one for the left side and one for the right.

Is it safer than lifting the earth on my power cable?

Yes. It breaks the loop in the audio path, so all your equipment stays properly earthed through the mains.