Introduction
Kojo Seiko Co. Ltd is a medium-sized company located in Hirakawa City in Aomori, Japan. Established in 1990, they are involved in a variety of electronic-related businesses ranging from power supply design and manufacturing to audio accessories.
Description
The Crystal EP is a virtual earth product that improves the grounding of audio equipment. The device is a barrel-shaped plug with various connectors available :- RCA, 3.5mm mini plug, banana and spades. The barrel contains 100 cm2 of high-purity aluminum foil treated with a special etching process to create cavities that increase the surface area to 11,000 cm2. The rear of the Crystal EP plug unscrews to accept a grounding cable for connection to the optional Crystal E Ground Box.
The Crystal E Ground Box is a compact metal ground box that houses an eight-layer plate structure that functions as a virtual ground. The plates comprise a combination of stainless steel, brass and copper plates. The plates are stacked, with a 0.5mm air gap between each plate. The box measures 80mm (W) x 35mm (H) and 111mm (D) and weighs 775 grams.
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| Picture taken from Kojo's website |
There are two screw terminals at each end of the box. One terminal is used to connect the grounding cable to the component or Crystal EP plug, while the other end is used to daisy chain a second Crystal E Ground Box. Two ground cables of 1.2m length are thoughtfully provided in the package, one with spades on both ends, and the other with a spade and RCA plug.
You can use the Crystal EP plug alone, or connected to one or more Crystal E Ground boxes. Alternatively you could use the Crystal E Ground connected directly to the component in question.
The Crystal EP Plug is made out of three pieces. The first piece is the termination plug and is interchangeable. The second piece is the main housing, and the last piece is the screw terminal that accepts the spade-terminated grounding wire that connects to the E Ground Box. This allows you to easily change the termination plug in case your needs change in the future, and also to stack the plugs if required. How you apply this product in your system is limited only by your imagination.
Sound Quality
Kojo is not my foray into grounding products, being a long-time user of Entreq ground boxes. Grounding accessories take a bit of experimentation to get right, with the results being very much system and component-dependent. Kojo products come in at a lower price-point compared to Entreq and are more compact, allowing you to deploy them in tight spaces.
The Crystal EP Plug increased focus and vocal texture, with more bass power. Dynamic contrast increased with instruments and vocals becoming more distinct. The effect was very noticeable with a 3.5mm EP Plug inserted into a Creative Soundblaster X4 DAC/headamp, with similar results pairing an RCA EP Plug with a Schitt Audio Freya+ preamp. Using twin RCA EP Plugs (on an unused input and output socket) increased the effect, but also sounded a bit too forceful and artificial for my taste.
Linking the EP Plug to a Crystal E Ground Box increased the level of refinement across the board, and added a calm sereneness to the music. It also added midbass weight which balanced out the extra energy on the midrange and treble. This turned out to be my favourite combination in listening tests.
As counter-intuitive as it sounds, do also try grounding the phono stage in your integrated amplifier (even if you don't play records). Attaching the Crystal E Ground Box to the ground lug of the Marantz 40N gave great sonic dividends, sorting out a vague and diffuse sound stage.
I tried adding Crystal EP Plugs to the negative terminal of my speakers. While the effect was similar, I found it to be more subtle compared to tweaking the source equipment. As I only had a single Crystal E Ground Box on hand, I was not able to ground both plugs.
Conclusion
The Kojo Crystal EP Plug and Crystal E Ground Box earn an easy Best Buy award from me. Improve your system for a modest outlay! However, as with all grounding products, do try before you buy since tweaks of this nature are highly system-dependent.
A big thank you goes out to Sky Audio Singapore, local distributor of Kojo products for providing the review samples. I personally purchased the EP Plug and Crystal E Ground Box.
Catch them too at International Sound & Sight Exhibition 2022. The show will be on 2-4 December at Holiday Inn Singapore Orchard City Centre, 11 Cavenagh Road, Singapore 229616.
Kojo Technology
Crystal E Ground Box - S$ 450 per piece
Crystal EP Plug - S$ 225 per piece (promotional price)
Sky Audio Singapore
28 Sin Ming Lane,
#05-137 Midview City
Singapore 573972
http://www.skyaudio.net