The German manufacturer Inakustik originally started as a maker of audio cables but is increasingly focusing on filters designed to rid mains voltage of high-frequency interference signals and DC components. Recently, between their series of unfiltered plug blocks and available mains filters in 43 cm cabinets, they have released a range of filters that, like a power strip, can find a place behind the furniture of an audio system. The AC-3200 series comprises three filters, each with a specific purpose. Inakustik has avoided the temptation of an all-in-one solution, which always has its drawbacks because compromises have to be made. From the three types – a DC blocker, a parallel filter for digital devices, and a series filter for analogue equipment – I specifically requested Filter Type I, the series filter. Supplied for the review is a Referenz AC-1205 AIR power cable. Because I am very curious about an AIR CAT cable from Inakustik, I also had one included with the shipment.

AC-3200 Filter Type I
When it comes to appearance or weight, Inakustik holds the strongest card. The brushed aluminium plug block is surprisingly heavy and robustly constructed. On the side is a C20 mains inlet, and on the top we find six Schuko outlets. They grip the mains plugs of connected devices firmly. A simple power cord is included, which is quite nice because not everyone has a C19 cable lying around. A better power cord is highly recommended.

The Type I filter, with a total capacity of 3680 Watts, directs the current through coils to the equipment and is intended for analogue devices such as amplifiers, pre-amplifiers, turntables, etc. Filter Type II is intended for streamers, DACs, and switches. The DC blocker is for those suffering from humming transformers. With my largely analogue setup and linear power supplies, a Type I is the most obvious choice here at home.

The AC-3200 filters are a completely in-house development by Inakustik and are manufactured in Germany. Internally, the filters use heavy-duty OFC copper strips with a cross-section of 16mm² to carry the voltage to the outlets. This prevents loss of dynamics and guarantees maximum current draw for each connected device. The coils, placed in series with the equipment, block the distorting components that ride on our mains network. This removes agitation from the playback, makes the musical background quieter, and prevents listening fatigue. Details are therefore easier to perceive in the music. Inakustik consciously chose to omit indicator lights and switches.

Their creed is: if you want to block interference from outside, you shouldn’t add it again from within. The block itself measures 512 x 77 x 77 mm. A small tip for Inakustik: a few adhesive rubber feet in the box would be welcome to keep the block free from the surface.

AC-1205 AIR Power Cord and CAT-2405 AIR Ethernet Cable
For those unfamiliar with Inakustik’s AIR cables, here’s a brief explanation of the principle. When it comes to insulating current-carrying wires from each other, the best conductor is air. But you can’t just use air. For safety, insulation around each conductor is always necessary, and you need to find a way to keep the different wires apart from each other. Inakustik does this by running the individually insulated wires through plastic clips and twisting the clips relative to each other, creating a helix shape.

In the past, Inakustik did this only up to a small section before the plug; in the series where the model number ends in a 5, the principle is carried through all the way into the plug itself, as seen in the AC-1205 and AC-2405. The clips keep each other at the correct distance. This method of construction minimizes both the cable’s own capacitive effect and its inductance – two electrical properties that can only limit the transmission of current and signal, never contributing to a better result. The individual conductors consist of braided, thin copper wires (silver in the more expensive types) covered with insulation. Around the wires and clips comes a braided sheath made of tinned copper to ward off external influences and serve as a ground conductor in power cords. In an AC-1205 cable, four conductors of 0.75mm² each are used, resulting in 2 x 1.5mm². The contacts of the plugs used have a gold coating. Despite the AIR Helix approach, an AC-1205 is only 13 mm in diameter and quite flexible to lay.

One of Inakustik’s most recent developments with AIR Helix technology is the CAT-2405 AIR LAN cable, an Ethernet cable that fully meets the CAT 8.1 specification with a bandwidth of 2000 MHz and a throughput of 40 Gbit/s. This is a cable you would use as a connection between an Ethernet switch and a streamer – where you benefit most from a better Ethernet cable. The construction of a CAT-2405 AIR is no different from all other AIR cables, although the clip is specially designed for this application. Over the clips, there is again shielding to avoid external interference. Critics will insist that digital is only about ‘zeros’ and ‘ones’, but that is really too simplistic. A digital signal consists of a voltage between zero and five volts travelling over the wires – a voltage that builds up and decreases, not abruptly 0 or 5. This build-up and transmission are hindered by capacitive influences, losses in insulating material, and impeded by noise and electromagnetic influence from outside.

The result can be an irregular voltage curve, noise entering via an Ethernet connection, all leading to jitter, component load, and extra current draw to correct errors. To meet international requirements for CAT cables, there is not only an overall copper braid shielding, but each pair of conductors is also shielded again with a conductive foil. The copper conductors of the cable are terminated in gold-plated brass RJ45 connectors, which are rotatable through 90 degrees, allowing the CAT-2405 AIR to be connected stress-free, in contrast to other Ethernet cables that sometimes have to be forced into tight bends behind a system. The cable is thick, with a diameter of 25mm. It is available in lengths of 1 meter, 1.5m, 2m, and 3m.

How, Who, What, Where
My usual test setup is ready. Hardware consists of an Auralic Aries G1 streamer with a power supply upgrade. A Metrum Acoustics Adagio DAC, an EAR/Yoshino 8L6 power amplifier, and two Falcon Acoustics LS-3/5A loudspeakers with Townshend Maximum Supertweeters. For Ethernet, a Melco S100 switch with Keces power supply is permanently connected. Normally, an Audes ST-900DC is my mains filter with an AudioQuest Tornado power cord attached; for now, those two are going into storage.

The choice of cabling is largely Inakustik from my own possession: NF-2404 AIR RCA interconnects, an AC-2404 AIR HQ power cord for the amplifier, and LS-2404 AIR speaker cable. Other cords are from Ricable and Audes. My standard CAT cable is an AudioQuest Vodka; this will be swapped with the CAT-2405 AIR. The AC-1205 AIR power cord sent by Inakustik is attached to the AC-3200 plug block. A hardware store quality plug block with a fixed cord is placed next to the AC-3200 for comparison. A mix of classical, jazz, and singer/songwriter music was chosen.

Normally, I would indicate what happens with various tracks, but with changing the power supply, that’s too difficult. The whole system has to be turned off, on, warmed up, and then listened to again repeatedly. So, I choose to describe general impressions of what I played. Albums that came by included ‘Nightbird’ by Eva Cassidy, ‘Cantado’ by the Bobo Stenson Trio, ‘Homage’ by Vilde Frang, ‘Birds that flew and ships that sailed’ by Passenger, and ‘Behind closed doors’ by La Serenissima.

Clean Power
Going back from a beautiful, lovingly and carefully constructed power supply to a hardware store plug block is a punishment. Gone is my rounded and pure playback, replaced by a hard timbre where a lisp on a voice is exaggerated. Bass becomes messy and loses definition. The stereo image, which normally has depth and height, shrinks to within the speakers and becomes flat. Anyone in the year 2025 who still doesn’t want to do anything about their power supply but does own a nice audio system is seriously shortchanging themselves. At least, that is my experience and my opinion. The mains network in the Netherlands is fortunately still stable, neatly maintaining the voltage at 230 Volts, but it brings along the necessary distortion alongside the mains voltage.

With an Inakustik AC-3200 Type I power strip with built-in filters and an AC-1205 AIR power cable, I get very close to my normal setup, for less than half the price. Unfortunately for you, reader, it’s not a one-to-one replacement if you were hoping for that. First, the positive points: despite using filters in series with the outlets, dynamics remain fully preserved. Inakustik has succeeded in not introducing a restriction, a common ailment of other, cheaper filters. Calmness in playback is also preserved, and after playing numerous albums, there is no tendency to turn the music off or down due to irritation or listening fatigue. The stereo image remains intact, extending sideways, with depth if the recording possesses it, and with placement of voice and instrument at the correct height. The playback is clear and open but unfortunately lacks some of the micro-details that a more expensive solution manages to preserve.

Although the playback is still slightly harder in timbre compared to a hardware store plug block, an Inakustik AC-3200 Type I with AC-1205 AIR power cable is a revelation. The whole system perks up; restlessness is gone, sharpness is gone. A violin like Vilde Frang’s starts to float through the room again.

If I conjure up another plug block from somewhere, one recommended for audio with a corresponding power cord, it sits roughly between the hardware store and Inakustik in terms of playback, but it remains a step backward that you don’t want. I don’t want it. The somewhat clearer presentation of Inakustik is probably very welcome for a somewhat lethargic system, waking it up. My EAR/Yoshino amplifier itself is already on the clear side, and even then, there is no accumulation of clarity that threatens to become unpleasant. There is absolutely no sign of aggressiveness.

The fine properties were likely contributed to by the fact that the Inakustik filter and Inakustik power cord were under power for a few days before being deployed. Filters and cables also require some burn-in time, in my experience. For those wanting to get the very most out of it, I can recommend experimenting with the order in which appliance plugs use the six outlets. Through some swapping, I achieved subtle further improvement by plugging my amplifier into the outlet farthest from the mains inlet, and the sources close to the inlet. Honestly, I don’t know if I would blindly recognize the differences the next day. But sometimes every little bit helps. What I can also mention as positive is the form factor of the AC-3200 Type I (and Type II and DC Blocker). The block doesn’t demand extra space in your rack like larger filters or my Audes do. You place it behind your rack. The outlets have contacts that grip well. An earth connection is necessary to guarantee optimal performance; operation without is possible if necessary and is 100% safe in any case.

Do Ethernet Properly
And then there’s the CAT-2405 AIR Ethernet cable, which also had some hours on it. I place it between my Melco switch and Auralic streamer, a connection running at 100 Mbit. So, all in all, I only use two of the four wire pairs. Several cables have played in that spot over the years, but my AudioQuest Vodka always remained in that place. With the Inakustik CAT-2405 AIR, it makes me itch to finally do an upgrade. This Inakustik is softer in nature than AudioQuest. Rounder, kinder, more pleasant. In a slightly more generously dimensioned stereo image, I more easily discover the semi-hidden micro-details in various recordings that I certainly know well. These are subtle sounds like the brush on cymbals, the landing of a bow on a violin string, the hammer striking a piano string. Precisely that, and more, for which you invest in a costly system. The CAT-2405 AIR presents itself as a very pleasant cable; I can’t catch it in any negative property, and it certainly ranks among the top of Ethernet cables available on the market. I admit that a CAT-2405 AIR might be more vulnerable due to the AIR Helix construction, but for those who don’t need to swap cables as often as the undersigned, that won’t be a problem. Connecting is certainly more pleasant with the rotatable connectors. With some devices, like my Auralic player, the Ethernet sockets are recessed behind the panel rather than flush with it; there, the small tab on the connector makes it difficult to unplug the cable again. Caution is advised!

Inakustik is a company where in-house research, material knowledge, measurement, listening, common sense, and in-house manufacturing go hand in hand. The German company never fails to surprise me with products that, while not among the cheapest on the market, are certainly among the better ones in terms of playback characteristics. It’s no coincidence that I am increasingly switching to AIR Helix products in my own systems.

Cables perform neutrally, adding no tonal colour of their own; as you climb the series, you retain all the good qualities and gain more detail, air, and calm in your system. A new product like a CAT-2405 AIR Ethernet cable builds on that. The standards set for cables are always met. This is important for all digital signal transmission, whether it’s USB, AES/EBU, S/PDIF, or Ethernet. The construction of AIR cables can only be done by hand, in-house at Inakustik in Germany, which makes the price higher. It is what it is; the performance matches it, and that determines the true value.

Thoroughness
Inakustik has been researching the phenomenon of mains pollution for years and offers a range of products for this purpose. The filters in a plug block like the AC-3200 Type I have received a great deal of attention, just like in every other Inakustik Power Conditioner. Knowledge and experience gained for the top model AC-4500 have been incorporated into these power strips. With good results. I dare to recommend this block with confidence to anyone who takes their audio system seriously and is looking for better playback than is achievable from normal plug blocks. Given the finish and the achievable improvement, the price for an AC-3200 is more than fair. It deserves a good power cable, such as the AC-1205 AIR supplied by Inakustik, which was used throughout. Well-shielded, made according to the proven AIR philosophy, and with properties like all other AIR Helix cables and cords. Together, a successful combination.

AC-3200 Type I with AC-1205 AIR:

Positives:
+ Bring calm to the playback
+ Exhibit no loss of dynamics
+ Six equivalent outlets
+ Current distribution via 16mm² copper traces
+ AC-1205 AIR is a flexible cable
+ Solid, firm-gripping plugs
+ Excellent finish for both
+ Products exude solidity and confidence

Negatives:
– No feet included
– A better power cord like the AC-1205 AIR is a must-have
– AIR Helix construction remains somewhat vulnerable

CAT-2405 AIR:

Positives:
+ Meets CAT 8.1 standard
+ Beautiful, rounded timbre
+ Pleasant presentation
+ Subtle and detailed
+ 90-degree rotatable connectors
+ Flexible

Negatives:
– Connector and cable are vulnerable due to the AIR Helix construction
– Thick cable
– Small tabs on the connectors