DC Blocker Trap Filter – Assembled in Case – v.3

 105.60 108.00 Incl. VAT
 88.00 90.00 Excl. VAT

Fully Assembled DC Filter/Trap/Blocker in a steel case with ability for mounting different AC Outlets types and the value of DC Blocking voltage depending the customer’s choice.


90Nowadays the AC mains network is heavily polluted by various domestic appliances, industrial electrical consumers etc. This can lead to buzzy toroidal transformers (especially the power ones). Proposed DC trap (blocker, filter) will remove or at least lower the 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 (

Here is offered a fully assembled DC Blocker in metal case. It is a successor of the very successful second version of the unit.

It retains most of the previous unit’s abilities but for the first time now the customer can chose a board with 6 discrete diodes which increases the ability for DC blocking up to 2V.

The possible variant os DC Blocking voltages are given on schematic below:

Two variants for number of protective diodes.

Dimensions of DC Blocker: 122x76x140 mm. (WxHxD).
Weight: ~ 0.95 kg.
For detailed description of PCB and schematic, please see my other items for sale: PCB for DC Trap Blocker Filter for toroids and DC Blocker Trap Filter – Populated PCB.

DC Blocker is built with following parts:
MASSIVE 47 000 uF EPCOS/KEMET capacitors (upgrade over the older 33000uF)
– Six high-current diodes (2V DC Blocking voltage) or one bridge rectifier (1.4V DC Blocking voltage)
– 10W power resistor
– High-quality film bypass capacitor
– MOLEX 3-terminal connectors for AC input/output
– Schurter IEC power inlet with fuse
– High-quality AC Power outlet (Schuko, French, Euro-American, United Kingdom) or IEC C14 outlets
– steel case black powder coated
– 4 small rubber feet underneath the case.

As you can see from the pictures DC Blocker is offered in 6 different variants of AC outlet – Standard European (German Schuko type), Euro-American type, French type, United Kingdom type and with IEC C14 outlet.

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 8A 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.).

Since some people need a more power, a DC Blocker version with C19 IN and OUT Mains connectors is offered too (see pictures in the gallery). This version does not have fuse and varistor on the input – just C19 input socket -> DC Blocker board -> C19 output socket. This allows the max. handled current to be raised to 15A.

And even if you think that all sockets (IN/OUT) just hamper the AC power, solution is offered: DC Blocker without Input/Output sockets but with cable glands for direct cable attachment to the board – see pictures in the gallery. Cables with outer diameter of 10 – 16 mm. can be attached to the Blocker via cable glands.

The terminal blocks used in the C19 and Cable glands versions are bigger than standard ones in order to accommodate cables up to AWG-11.

Note: Since some of AC outlet types are not widely used in Europe, please ask for availability before committing the order. Also, when completing purchase, note the type of AC Outlet you want to be used with the Blocker.

What the buyer will receive:
The package will contain 1 pcs. FULLY ASSEMBLED and tested DC trap/blocker/filter for toroidal transformers (toroids) 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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Fully Assembled DC Filter/Trap/Blocker in a steel case
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 4 reviews
 by Steve
DC Blocker v.3: brilliant!

My recently acquired Naim power amp hums intermittently due to DC noise on the mains. Whilst the hum varies in volume and can happen apparently randomly, I have identified one culprit; the espresso machine in the kitchen! Hence it was easy to do an A/B comparison with ATL’s DC blocker. Before: an audible hum when coffee is being pumped, after: silence. This ATL device replaced a clutch of more expensive ‘passive’ mains silencers that had no effect, so I’m delighted. What I hadn’t expected was the improvement in overall sound quality now the Naim isn’t battling with mains noise. Bass goes a little deeper, soundstage is wider and instruments are more clearly delineated, and there is no negative impact on dynamics that I can hear. I’m listening now to a live album I know well and it’s bigger and bolder than ever. What a great purchase!

 by Emulator II
Enjoy The Silence

Actually, I had come to terms with the fact that audible transformer hum is the pill you have to swallow when you decide on devices with this otherwise stable and, above all, long-lasting type of power supply via toroidal transformer. And yes, every transformer hums. But with the help of this high-quality, well-made, yet affordable device, the hum has shrunk to levels that are finally inaudible at the listening position during late-night listening sessions. My trusty PA power amp can finally be placed where it belongs anyway due to its impeccable technical performance - in my hi-fi rack.
One of the best purchases in a long time. Just great! Thanks very much!

 by David

I had to come to the conclusion that the occasional hum in my amp was caused by a DC component in the power supply network. This little box is resolving the issue, doing the job as expected. Very nice build quality. The must surprising effect is the bass range is preety improved on my hybrid class A/B tube/transistor amp.
The overall price/quality ratio is amazing. Shipment was very fast from Bulgaria to France!
Thank you Mr. Tsankov!

 by Michael

Absolutely terrific little box and does exactly what it says on the tin. It really lets your equipment sing the way it should.

Additional information

Weight 0.93 kg

EU Schuko, UK Plug, US Plug, French Plug, Cable Glands, C14 Outlet, C19/C20 Outlets, Australian Plug, Switzerland Plug, Brazilian Plug

DC Blocking Voltage

1.4V (Bridge Rectifier), 2V (6 Discrete Diodes)