Combined module DC Blocker (trap, filter) & EMI/RFI/Common Mode Filter – Assembled in Case

 132.00 138.00 Incl. VAT
 110.00 115.00 Excl. VAT

Combined module DC Blocker & EMI/RFI/Common Mode Filter in steel case with ability for mounting different AC Outlets types.


Nowadays we use an enormous amount of Switched Mode Power Supplies (SMPS) equipped domestic appliances, industrial electrical consumers etc. in our everyday life. These appliances can cause not only a DC shift in the AC Mains which leads to buzzy toroidal transformers (especially the power ones) but they also throw a great deal of RF hash which sneaks and disturbs the precious analogous networks of our audio equipment.

Here is proposed a fully finished and tested unit, assembled in steel case comprised by two sections – a DC Blocker/Trap/Filter and a Common Mode Filter (CMF).
Schematic of the unit can be seen below:

Combined module DC Blocker & Common Mode Filter
Combined module DC Blocker & Common Mode Filter

The DC trap section will remove or at least lower the toroidal transformer buzzing.
Schematic is similar to this one used in well known Vladimir Shushurin’s Lamm-1 amplifier. An article with in-dept explanation of how DC blockers work can be found on Rod Elliot’s site (

The Common Mode Filter will deal with the high frequency pollution in the AC Mains Network.
It was inspired by the very successful “Felix project” (

In-depth explanation and examples of Common Mode Filters can be found here:

In the process of CMF simulation the following results were outlined:

– The damping resistors lower the spike in frequency response with approx. 20 dB

CMF without damping resistors
CMF without damping resistors
CMF with damping resistors

– Removing the load-side shunt capacitors (as supposed in the Fo-Felix version of the filter) will give us a smoother frequency response but the corner frequency is shifted to the higher frequencies approx. 25 times

CMF without load-side shunt capacitor


PCB specifications:

Dimensions of PCB: 100×115 mm.
PCB type: FR4 1.6 mm. Copper thickness: 70 um (2oz). Surface finish – Nickel Gold (ENIG).

The board is TWO-layer design which allows the PCB traces to be doubled on the TOP and BOTTOM layers thus doubling the current handling capabilities of the board. All current conducting traces are widened as much as possible which additional raise the max. handled current.
PCB has solder mask coating on top and bottom layer for best durability.
Silk screen with parts layout is placed on the top of the PCB.

The unit has following abilities:

DC Blocker Section
It is calculated to handle max. current of up to 16A
– On the board are mounted 6 discrete high-power diodes 10A4 which yield the max. DC Blocking voltage of approx. 2V.
– two MASSIVE 47 000 uF EPCOS/KEMET capacitors (the bigger is capacitance, the higher are handled currents).
– one 10W power resistor.
– one bypass WIMA MKS4 400VAC capacitor.

Common Mode Filter Section
It is calculated to have a corner frequency of approx. 20 kHz and max. handled current of 20A with the parts used
– 4 pcs. X2 type safety polypropylene capacitors
– 2 pcs. Y2 type safety polypropylene capacitors
– High-Power Wuerth Electronic’s Nanocrystallyne Common Mode Choke

The PCB is mounted in a steel enclosure with following characteristics:

– Schurter IEC power inlet with fuseholder
– Schneider AC Power outlet (Schuko, French, Euro-American, United Kingdom or Italian).
– steel case black powder coated
– 4 small rubber feet underneath the case.

Dimensions of Combined module DC Blocker & EMI/RFI/CMF: 125x165x75 mm. (WxDxH).
Weight: ~ 1.25 kg.

As you can see from the pictures Combined module DC Blocker & EMI/RFI/CMF is offered in 5 different variants of AC outlet – Standard European (German Schuko type), Euro-American type, French type, United Kingdom type and Italian type (double AC outlets!!!).

Note for United Kingdom customers (mainly): Due to specific of the UK wall plug, attaching it to the Blocker can be uncomfortable sometimes when DC Blocker’s AC Outlet is in the standard position. Hopefully it can be easily rotated to 90 deg. clockwise or anti-clockwise (see attached pictures).

Of course such rotation can be done with all other AC Outlets too! Just let me know what do you want upon purchase.

A surge protection with 250V rated varistor and 10A fuse (Schurter Slow-blow type) is incorporated at the AC input (fuse can be replaced with 10A one upon request).

All parts used are freshly obtained from reliable sources (Mouser, Farnell, Digi-Key etc.).

What the buyer will receive:
The package will contain 1 pcs. FULLY ASSEMBLED and tested Combined module DC Blocker & EMI/RFI/CMF in steel case.

The unit will be shipped with Priority AirMail Registered (or equivalent courier service where applicable). The tracking number will be sent to the customer after shipment.

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Combined module DC Blocker & EMI/RFI/Common Mode Filter in steel case
Average rating:  
 1 reviews
 by Holger Dech
Works 🙂

Ich habe den kombinierten DC-Blocker & EMI Filter, (Kaltgeräte-Eingangsbuchse 10A Sicherung), vor meine Audio/Video/Computer und Fritz-Box installiert. Der Effekt per Soundcheck ist positiv - mehr Ruhe und mehr Substanz. Das Bild (TV und Monitor) ist auch besser geworden. Das DSL-Modem der Fritz-Box produziert etwas weniger Fehler.
Die 4 x 1µF X2 Caps reduzieren (differential Mode) Störanteile. Gemessen mit einem Greenwave Broadband EMI-Meter (3KHz-10MHz). Die stromstarke (20A) Common-Mode Spule/Drossel wird wohl erst ab ca. 10 MHz, oder höher, eine Dämpfung, sprich Common-Mode Störanteil-Filterung ausspielen können. Die zwei potenten Y2 Kondensatoren (Common-Mode) vs. Phase und Neutral-Leiter, Ableitung über den PE-Erdungsschutzleiter ergänzen im unteren MHz-Bereich die Wirkung der Drossel.
Pro Gerät sollte man Filter einsetzen, welche an die max. Stromstärke des einzelnen Gerätes angepasst sind. Sprich für ein Modem, Router oder einen DAC genügen EMI-Filter mit 1A bis 3A. Eine 1A Drossel hat eine deutlich höhere Induktivität (mehr Dämpfung) als zum Beispiel eine 10A Drossel.
Die Kombination DC-Blocker + EMI Filter ist durchdacht, das Layout hat Hand und Fuß 🙂

Additional information

Weight 1.25 kg
AC Outlet Type

EU Schuko, UK Plug, US Plug, French Plug, Australian Plug, Switzerland Plug, Brazilian Plug, Cable Glands

Protective Diodes Type

Regular, Fast TO-220