iFi DC Blocker + DC Offset Voltage Blocker

What You Need to Know

What Is the iFi DC Blocker+?

If you’ve ever put your ear close to your amplifier and heard a low, steady hum coming from inside the chassis, you’re not imagining things. That mechanical hum is usually caused by your amplifier’s power transformer vibrating. And the reason it vibrates? A small amount of DC (direct current) voltage that shouldn’t be there has snuck into your AC mains power.

Here’s the short version: Your wall outlet is supposed to deliver pure AC power that alternates evenly around zero volts. But in the real world, various appliances, dimmers, motors, and other devices on your electrical circuit can create a DC offset—a slight imbalance in the AC waveform. When that offset reaches your amplifier’s toroidal transformer, the transformer becomes “saturated” and starts to hum.

The iFi DC Blocker+ is a small, clever device that plugs right into the IEC power inlet on the back of your amplifier (that’s the rectangular socket where your power cord connects). It sits between your power cord and your equipment, and it blocks any DC voltage from getting through. No DC means no transformer saturation, and no saturation means no hum. It’s that simple.

Why Does It Matter?

The DC Blocker+ uses iFi’s ZERO DC Block technology to block incoming DC up to 1,200 millivolts. That’s enough to handle the vast majority of DC offset problems found in residential power. And it does this without affecting the AC power your equipment needs to operate normally.

This is the “+” (plus) version, which means it’s designed for high-power equipment. With a continuous current rating of 10A and a maximum current rating of up to 14A, it can handle large amplifiers with big toroidal transformers—exactly the kind of equipment most prone to DC-related hum. It supports amplifiers drawing up to 1,100 watts on a 110V circuit (or 2,200 watts on 220V).

The DC Blocker+ also retains EMI (electromagnetic interference) shielding, so it’s not just blocking DC—it’s maintaining protection against radio-frequency noise too. The hospital-grade IEC connectors ensure a solid, reliable connection, and the entire unit is UL listed with flame-resistant materials (UL94-V0 rated).

At just 3 inches long and 2.8 ounces, it’s compact enough that it won’t block neighboring power sockets or put strain on your equipment’s IEC inlet.

An Important Note: What It Does and Doesn’t Fix

The DC Blocker+ is specifically designed to eliminate mechanical transformer hum caused by DC offset on the mains. This is the hum you hear coming from inside the chassis of your amplifier, not from your speakers.

It will not fix hum caused by ground loops (buzzing from your speakers), phono stage interference, cable faults, or gain-mismatch hiss. If your hum is coming through your speakers rather than from the amplifier chassis itself, the issue is likely something else. Not sure which kind of hum you have? Give us a call at 800-942-0220 and we’ll help you diagnose it.

Who Is This Best For?

Your amplifier or integrated amp has a noticeable mechanical hum coming from inside the chassis, especially when the room is quiet.

You have a large amplifier with a toroidal transformer that’s particularly sensitive to DC on the mains.

You live in an area with “dirty” power—older wiring, shared circuits with heavy appliances, or frequent dimmer switch use nearby.

You want a simple, plug-and-play solution that doesn’t require any wiring, tools, or modifications to your equipment.

You need a DC blocker rated for high-power equipment (10A continuous) rather than lighter-duty devices.

How Does It Connect?

Installation could not be easier. Unplug your power cord from the back of your amplifier. Plug the DC Blocker+ into the IEC inlet on your amp. Then plug your power cord into the DC Blocker+. That’s it—you’re done. No tools, no settings, no configuration. It’s a “fit and forget” solution.

The DC Blocker+ works with any equipment that uses a standard IEC power connector (the three-prong rectangular socket found on most amplifiers, receivers, DACs, and other audio components). It’s globally compatible with voltages from 90V to 250V.

If you also have a ground loop problem, iFi makes a separate product called the GND Defender that can be used in combination with the DC Blocker+.

What’s in the Box

• iFi DC Blocker+ unit
• Product documentation

What Are Reviewers Saying?

Professional reviews of the DC Blocker+ specifically are limited, but the original iFi DC Blocker has been well received by the audio press.

Pairs Well With

Building a quieter system? Here are some great companions:

• iFi GND Defender — If you have both transformer hum and ground loop buzz, the GND Defender tackles the ground loop side. Use both together for the quietest background.
• Power Cables — A quality power cable between the DC Blocker+ and your equipment completes the chain. Browse our Power Cables.
• Power Conditioners — For full-system power protection and conditioning, browse our Power Conditioners.

Features & Specifications—Benefit-Driven

DC Blocking Performance

ZERO DC Block Technology — iFi’s proprietary technology blocks incoming DC voltage up to 1,200 millivolts. This eliminates the root cause of mechanical transformer hum in amplifiers and other audio equipment with toroidal power supplies.

High-Power Rating — With a continuous current rating of 10A and a maximum rating of up to 14A, the DC Blocker+ handles large, powerful amplifiers without breaking a sweat. It supports equipment drawing up to 1,100W on 110V circuits or 2,200W on 220V circuits.

EMI Shielding Retained — The DC Blocker+ doesn’t just block DC—it also maintains electromagnetic interference shielding, helping keep radio-frequency noise out of your system.

Safety & Build

Hospital-Grade IEC Connectors — Premium connectors ensure a solid, reliable connection to your equipment’s power inlet.

UL Listed — Independently tested and certified for safety.

Flame-Resistant Materials — The IEC socket, connector, and chassis use fireproof polymers rated UL94-V0.

High Dielectric Strength — Rated at 1,500 VRMS for reliable insulation between circuits.

Design

Compact and Lightweight — At just 3″ × 1.8″ × 1.3″ and 2.8 ounces, the DC Blocker+ won’t obstruct neighboring power sockets, cables, or connectors. It won’t strain your equipment’s IEC inlet either.

Globally Compatible — Works with voltages from 90V to 250V, so it functions anywhere in the world.

Plug-and-Play Installation — No tools, no settings, no modifications. Just plug it in between your power cord and your equipment.

Quick-Reference Specifications

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