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| Nevertheless, since I was already working on the Hypex modules, it was a no-brainer to also examine it for full-range duties. From an engineering standpoint, the class D amplifier looked like the perfect amplifier - tremendously fast and able to deliver huge currents into low impedances. On the Hypex website, they recommended power supply upgrades (and they even sell two versions of their power supply) and also better low voltage regulation for the input buffer (and they sell an upgraded regulator now). That got me to thinking about power supplies. There are two types needed for an amplifier - a low-current regulated voltage supply and an unregulated high-current supply. I discovered a couple of things that surprised me. First, the noise rejection on the voltage supply for a typical op-amp gets worse with increasing frequency; and that regulated voltage supplies have increasing noise with increasing frequency. Taken together, it seemed like a bad thing. Second, most current supply designs are based on the ability to deliver a constant current into a specified load. The first problem got me to thinking that since the PSRR of an op-amp goes down with increasing frequency, the voltage supply for the op-amp ought to have better noise rejection in the higher frequencies or at least be flat across frequency and not get worse. The second problem was trickier. If we can imagine an amplifier as a faucet for current and the input driving signal controls how much that the faucet is opened, then the power supply will be the pipes and the water tank feeding that faucet. Hence an amplifier is never a constant current load. Just as the pipes would rattle when you turn the faucet on and off rapidly, the power supply would also "rattle". The larger the water tank, the larger the pipes, and the faster you turn the faucet on and off, the more the pipes would rattle. It's an imperfect analogy but with music rather than sine waves or a constant draw, the amplifier would make the power supply "rattle"..... and the class D amplifier would be the worst of these. I enlisted the aid of Nigel Pearson, the English power engineer who is also designing for IsoTek, and the result of that collaboration was the SRVS Silent Running Voltage Supply to solve the first problem. I worked out the DPDS Dynamic Power Delivery Supply to solve the second problem (some of those designs are part of Genesis' trade secrets). |
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| FB: By going with solid state and admittedly hunting down all forms of distortion, supposedly beneficial or not, were you not afraid of falling into the common trap of sterility and lifeless audiophilia that you despise so much? |
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| GK: You and I are both tube-heads! I too had always associated distortion-free with emotionless, sterile and clinical until I met the owner of FM Acoustics, Mr. Manuel Huber (as colorful a character as you've ever met!). He explained to me the difference between real music reproduction and euphonic distortion, a conversation I've remembered ever since. It's the difference between a freshly shucked Belon oyster and the cooked Singapore oyster omelette with hot chili sauce. The latter was invented because the oysters they had were not fresh and needed the additional sauces to hide the imperfection. The freshly | |||||||||||||||
| shucked Belon brought across the ocean breeze, the tangy metallic brine that bring you back to the time you walked barefoot on the Brittany beaches. A distortion-free system would bring the musical performance back to life and transport you to the event. The euphonic distortion, while pleasant and inviting, is a totally different musical event, one that has been colored and re-cooked. |
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FB: The amplifier I am reviewing sits in the middle of your product line. Have you voiced the various versions of the Reference amplifier for different purposes? GK: Besides greater headroom and greater macro dynamics into lower impedance loads, I have voiced the amps so that there is little sonic difference. At 26dB, the gain of the GR180 and GR360 is the same so it won't be louder though the doubling in power means that the GR360 can theoretically go 3dB louder at full power for sine waves. However, for music, it does not translate that easily. If I was pressed to describe the difference, I would say that the GR360 when compared to the GR180 is a little more at ease and a little more effortless (and the monoblocks even more so). FB: What can you tell our readers about the external power supply? It weights a ton! GK: Yes, the toroidal transformer is monstrous. That is why the power transformer hums a little. The transformer for the 360-watt amp is rated at 1,850kVA, the one for the 180-watt amp at 1,150kVA. Before you ask why those ratings, they sounded best. Smaller lost macro dynamics, larger slowed the music down. |
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FB: The amplifier provided for review came with an Isotek power cable. Is that a standard feature? GK: I did try other power cables and I even tried designing my own but the IsoTek sounded better. The IsoTek cable is solidly constructed, has a high coverage low resistance braided shield and high purity annealed oxygen-free copper conductors. Most important was that the cable not have a sonic signature. There are a number of good mains cables but many of them had sonic characteristics that would alter the sound of my amplifier. This cable will not come included. However, all Reference amps will include a coupon for a deep discount on an IsoTek power cord. FB: Do you also use IsoTek cable internally? GK: No we don't but I probably spent as much time on the design and routing of the wiring of the amplifier as I did on the power supply. Thicker does not translate to better. In the M60s and I60, we used a cotton sleeve that resulted in essentially an air dielectric over a solid core of copper. I wanted to move back to stranded wire but a cotton sleeve would not work there. So I ended up with extremely heavily silver-plated copper strands (I call it strands of silver with a copper core). The reason for the heavy silver plating is so that the strands can be wound so tightly that the soft silver on one strand imprints on the other, resulting in a conductor that has both the advantages of stranded and solid-core. Over this we put a Teflon dielectric - not ordinary FEP or PFA but PTFE. Next to air, Teflon has the best dielectric properties for the purposes of the insulator on a cable to convey music. To further improve micro-dynamics and detail, the entire signal path is softly suspended to reduce any vibration to the wire. We lay the signal-carrying cables on a neoprene foam bed and also blanket the wires with another layer of neoprene. FB: You've mentioned already your very eclectic musical tastes but is there a disc that particularly helped you in voicing those amplifiers? GK: I use three recordings by Wynton Marsalis - Standard Time Volumes 1, 3 and 5. If I can hear the development of tone in his maturing styles, then the speaker or the amplifier or whatever I'm designing has sufficient transparency to show the tonal colors. The trumpet is one of the toughest instruments to portray accurately. It generates enormous power and at the frequencies where the speaker is most taxing to the amplifier. FB: Thank you very much Mr. Koh for your insights in how the GR amplifiers came to be. For our technically inclined readers, additional information can be found in the sidebar where I have gathered material and details from the various pieces of literature published by Genesis. |
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