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Passive AC filter

Acoustic Revive

Manufacturer: SEKIGUCHI MACHINE CO., Ltd.
Price (when reviewed): 3140 EUR (+ VAT)

Contact: YOSHI HONTAI | MuSon Project, Inc.


Provided for test by MUSON PROJECT


Images: Wojciech Pacuła

No 207

August 1, 2021

ACOUSTIC REVIVE is a Japanese company founded in 1997 and run by Mr. KEN ISHIGURO-san. It specializes in audio cables and anti-vibration products, but it also offers innovative ones, the ideas of which most often come from the University of Tokyo. We are testing one of the products used to filter the AC supply voltage, the RPC-1K.

RITING IN MAY 2017 that the ACOUSTIC REVIVE RPC-1 passive voltage filter is "one of the more expensive passive filters I know", what I really meant was that it was the most expensive filter of this type I reviewed (more HERE; accessed: 29.06.2021).

At that time, the product of the Japanese specialist costing PLN 11,900, who, apart from classic audio cables, also offers a whole universe of devices and "dings" to improve the sound of an audio system - from CD ionizers and demagnetizers, through anti-vibration elements, to cable supports, was a pioneering product at the time.

These products, although at first glance completely "crazy", are created in cooperation with Tokyo technical universities, for which they are often side projects to those intended for industry, usually medical and military ones, but not limited to these two branches. The head of Acoustic Revive, Mr. Ken Ishiguro-san, sees them as useful tools that can be adapted to home audio systems. The RPC-1 model, now available in the new RPC-1K version, can boast a similar genesis.


⸜ TECHNOLOGY The RPC-1K filter is used to minimize interference in the AC mains to which the audio system is connected. It is a parallel filter, that is, it is plugged into any power outlet, be it one in a power strip or a wall outlet. As we read in the company materials, it does not have to be a socket placed close to the system, because the filter fulfills its task when it is switched on anywhere in the house.

The company materials read:

This groundbreaking new power conditioner reduces very high frequency noise in the power path (emphasis - ed.). This produces a sound with improved dynamics and energy with a better signal-to-noise ratio. The unique circuit design with a combination of special coils allows only high-frequency noise to be removed. As no capacitors and resistors are used in the RPC-1K, there is no waste of energy in the RPC-1K. This gives the RPC-1K a unique ability to improve signal-to-noise ratio and transparency, but without acting as a filter, which often reduces dynamics and energy.

Earlier I mentioned the price of the previous version of the Japanese product, the RPC-1 model - which was bit less than PLN 12,000 which seemed almost a prohibitive amount, but when I listened to the THUNDER MELODY VACUUM INFINITUM BLACK, the Polish equivalent of the filter from Japan, costing PLN 22,000, I had no such doubts - I was, one could say, fully "converted" (or completely "f...ed up", depending on what we consider to be „common sense” in terms of spending money on a hobby).

Anyway, we connect the RPC-1K to a free outlet of an AC power strip, to which AC power cables are connected. Like all other AR products, this one is based on scientific research - in this case, of Mr. JUN SHIBATA. Mr. Shibata-san is a very interesting character - he is the man who developed the infrared computer mouse prototype that we almost all use today. While working on it, it turned out that the development of the prototype was hampered by high-frequency noise in AC power lines.

As I wrote during the test of the first version of the filter, based on his observations, Mr. Shibata-san built a filter that eliminated these distortions. It consisted of a set of capacitors, resistors and coils. His own contribution consisted in a special selection of a set of coils connected in parallel to the cold and hot supply line. This arrangement caught an interest of Mr. FUKUSHIMA, the head of the HWT company, working for the industrial sector. He bought the rights to this solution and based on them he developed an industrial filter that eliminates RFI noise.

The head of Acoustic Revive decided to use this study to clean the AC power line used by audio devices. So he started cooperation with HWT and on the basis of their industrial model he developed a more powerful circuit, tuned for use in audio systems, which features no capacitors. This is how the Acoustic Revive RPC-1 Power Supply Conditioner was created, the new version of which we are testing this time.

⸜ DESIGN Like its earlier version, the RPC-1K is enclosed in a large Hickory box, measuring 170 x 170 x 80 mm (width x depth x height), from which comes out a 37 cm Power Reference Triple-C power cable, terminated with a reference AC Furutech FI-E50 NCF (R) Schuko power plug with rhodium-plated PCOCC copper pins; the plug itself costs PLN 1650 (!). Let me remind you that the RPC-1 model was equipped with a simpler FI-E11 N1 (G) plug, also from Furutech.

The box cannot be opened, so the components used inside and their layout remain a company’s secret. It is known, however, that apart from the passive elements - coils - it contains all the materials used by Acoustic Revive to suppress vibrations and minimize noise, including powdered tourmaline, which releases negative ions. It is a crystalline boron-silicate material, belonging to the group of silicates, made of such elements as aluminum, iron, magnesium, sodium, lithium and potassium.

The letter 'K' in the name tells us something else. This Japanese company has launched a whole series of products this year, in which it used a new material - Kiyoh-stone. We have already written about it on the occasion of the test of the RWL-III ABSOLUTE acoustic panels, and we are preparing more tests of the products with 'K' in the name, for example a gramophone mat and artificial mass. In the listening section you will also find a table with a micro test of the cable supports.

As Mr Elia Hontai-san from the Muson company, which is a representative of Acoustic Revive outside Japan, wrote to me then, Kiyoh-stone is a rare earth element, the main ingredient of which is aluminum silicate. It is available at only one location in the Land of the Rising Sun, in Gunma Prefecture. As he says, this is no coincidence, because Acoustic Revive is located in the same prefecture.

The property of this material, which Mr. Ishiguro-san was keen on, is that it easily generates high intensity negative ions, the maximum of which is in the far-infrared rays. Kiyoh-stone generates up to 40 times more ions than tourmaline. This material was most likely used (although this is just my guess) in the form of paint that was used to paint the inside of the filter. Mr. Elia Hontai adds that it is one of the more expensive materials of this type available on the market, and only in limited quantities.


⸤ HOW WE LISTENED TO IT The AC Acoustic Revive power supply filter RPC-1K was tested in the HIGH FIDELITY reference system and compared to its older RPC-1 version. Both filters were plugged into the Acoustic Revive RPT-4EU Absolute power strip, and the latter, through a 2.5-meter Acrolink Mexcel 7N-PC9500 cable, to a dedicated Furutech NFC socket in the wall, to which a separate power line with its own fuse leads. I listened to the filter plugged into the socket in the kitchen separately

It was an A/B and B/A comparison with A and B known.

I would like to add that the supply voltage filters are sensitive to vibrations, so I always place them on platforms or - in this case - on anti-vibration feet. I used three Franc Audio Accessories ceramic Disc Classic feet for this purpose.

Recordings used for the test | a selection

⸜ CHARLIE PARKER,South of the Border, Verve/UMG Recordings UCCV-9479, „David Stone Martin 10 inch Collector’s Selection”, SHM-CD (1951-52/2013).
⸜ FRED SIMON, Remember The River, Naim Label naimcd081, CD (2004).
⸜ NAT ‘KING’ COLE, The Nat King Cole Love Songs, Master Tape Audio Lab AAD-245A, „Almost Analogue Digital”, Master CD-R (2015);
⸜ PINK FLOYD, The Endless River, Parlophone Records 4621333, CD + Blu-ray (2014).
⸜ SŁAWEK JASKUŁKE for RAFAŁ BUJNOWSKI, Music on Canvas, Sławek Jaskułke/Core Port PROZ-10063, CD (2020).
⸜ TANGERINE DREAM, Rubycon, Virgin Records/Universal Music LLC UICY-40131, Platinum SHM-CD(1975/2015);


KEN CHRISTIANSON, the man responsible in the 2000s for the characteristic, unique sound of Naim albums, the recording session of FRED SIMON, which appeared on the Remember The River album, I started the listening session with, prepared in a typical way for him. The three instrumentalists who took part in it were arranged in such a way so that the only microphones used during the recording, the stereo pair of AKG C414B-ULS, "heard" them equally loud.

However, because the sound of different instruments is picked up by the microphones in different ways, depending on their timbre, distance and method of emission, he placed Steve Rodgby's double bass on a platform and separated it from the leader's piano with a transparent screen. He treated Paul McCandless's saxophone and flute in a similar way, except that in his case he placed the screen on the side to dampen the echo from the Pick-Staiger Concert Hall at Northwestern University. The material was recorded directly on two tracks of the Nagra IV-S analog tape recorder, and he called the method in question True Stereo (more about it HERE; accessed: 30/06/2021).

An interesting thing - without a filter in the system, the sound of this album was excellent. The colors were not as vibrating, and the instruments as tangible as in the recordings where the microphones are placed right next to them (see the Three Blind Mice realizations), and yet the expression of the whole was incredibly natural and friendly. However, all I had to do was to connect the RPC-1K to a power strip, and the instruments gained mass, became larger, richer. Disconnecting the filter brought back the previous sound, which still felt great.

So it is not that connecting the Acoustic Revive filter will automatically transform the sound. But it is also clear that without it there is something missing in it - so much that with the filter the sound seemed more resolving, as if there were more “sounds” in it. The point, I believe, is that the filter extracts fine information from the noise, allowing the music to resonate in a more complete, complete and complex way. After a while we get used to the sound without a filter and it is beautiful again. But with each subsequent attempt, a period of being content with a sound without the filter shortens a bit, so that after some time we constantly miss what we get with the filter.

The Naim label recording belongs to the group of natural-sounding ones, so the influence of the tested filter could seem emphasizes - after all, the more natural something is, the faster we can notice the distortion of this naturalness. So I reached for the CD from start to finish constructed in a recording studio, the Rubycon by TANGERINE DREAM.

Its sound seemed to me even more susceptible to the influence of the Japanese filter. The sound was clearer with it, but also smoother. On the one hand, the individual sounds were placed closer to me, and on the other, they extended further into the stage, which made it seem as though they were a bit further away from me. A paradox, but it seems to me to result from the fact that the filter made the sounds of analog synthesizers three-dimensional, better defined, and thus their projection in space improved. And this is what I perceived as being both brought closer and further away from me.

It was also interesting that the sounds around me and from the sides - this is just such a recording - were clearer, stronger with the filter and had more "sounds" in them. Which, once again, confirmed my observation from the beginning of the listening session, that the Acoustic Revive filter reduces something "behind the sounds", some distortions that flatten them.

I had very similar feelings while listening to the The Nat King Cole Love Songs, released by the Chinese label ABC Records on a gold CD-R burned directly from the analog "master" tape. The voice without the filter was nice, big and palpable - sometimes more, sometimes less, depending on a recording (we're talking about a compilation). I liked it. The filter, however, caused a distinct change in the aspect ratio. The vocals had more depth with it, but more importantly, the orchestra, not always "sticky" with the vocals, was more natural with it, not so "separate" anymore.

⸜ WITH ‘K’ AND WITHOUT ‘K’ One of the reasons I didn't permanently install the first version of the filter on my system was that while it did a great job, it did what it was made for, the sound had a slightly emphasized attack with it and was a bit brighter. It wasn't its problem, or even mine, and it was a classic case of a product-to-system mismatch. In many other high-end audio systems, I am sure, it would be the perfect "tonic" used to break their performance out of boredom. For me, however, such an action was not needed, so I used it only from time to time.

The new version of the filter, the one with the letter 'K' in the name and Kiyoh-stone inside, causes the sound to lower rather than brighten up, which turned out to be a better option for my system. I would say that it is clearly a better product, because it was like that in my case, if it were not for the fact that the basic version of the filter, i.e. the one without the 'K' letter, is already very good. Ultimately, however, "here and now" counts, and in my case it means one thing: 'K' and only 'K' ...



The RCI-3HK ARE NEW cable stands from Acoustic revive (215 Euro / pc + VAT). They replace the RCI-3 model in the catalog, which I have been using for several years in my system. These stands consist of three main elements: a body made of Hickory wood (hence the name 'H') with a hollow chamber, a mixture of minerals poured into the chamber and a mahogany plate closing the whole from the bottom. Minerals convert vibrations into heat, also in the infrared range.

Compared to the older version of the stands, the mixture in question includes powdered Kiyoh-stone. This mineral perfectly ionizes and radiates energy in the infrared spectrum. The inspection also shows that the plate closing the chamber was made of a slightly different wood.

⸜ RCI-3H on the left, RCI-3HK on the right.

The new stands modify the sound in a delicate, but also desirable way. The sound with them is more focused, more concise and better defined. And at the same time it is also darker. It seems that there is more information, because both Nat 'King' Cole's vocals and Fred Simon's piano were bigger, clearer. And there was no brightening. It's not that you could hear more details, but - as it seems to me - greater resolution in the sound with the RCI-3HK stands. And I say this comparing them to the older version without 'K' in the name. Compared to cables laid on the ground, in this case the Siltech Triple Crown, the difference was very big.


THE BASIC TEST WAS DONE with a filter plugged into the power strip. After completing this part, I also tried it in other parts of the house, mainly in the kitchen. As I said before, the audio system has a separate power line with a separate fuse, so they are not exactly the same circuits. And yet also in this case the sound improved and no less than when the filter was placed next to the power strip. The only difference was that it took a bit longer for the changes to become apparent - when plugging the filter into the strip, they were immediate.

Anyway, the Acoustic Revive RPT-1K is a great product and, next to the Polish Thunder Melody Vacuum Infinitum Black filter, the best product of this type that I have heard at home. It changes the sound in a way that gives us more content, information and presence. The sound, however, is not projected towards us, it just becomes more three-dimensional and clearer. The first version of the filter was very good, but its new version of 'K' worked much better in my system.

RPT-1K is a product designed for all high-end systems, no matter what the sound preferences of the users.


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AC Power

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Power Supply Conditioner: Acoustic Revive RAS-14 Triple-C |REVIEW|
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