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Breakthrough Proprietary Phono Equalization
 Grado's model PH-1 phono preamp represents the successful solution to one of the most complex technical challenges in the field of audio that Grado Labs has ever tackled. The company's design goals were to create a truly superb sounding phono preamp that would work equally well with both low and high output cartridges with negligible noise. Furthermore, the phono preamp needed to have ultra-wide band pass, high overload, virtually perfect RIAA amplitude and phase coherency, and very low output impedance.
It's no great surprise that Grado succeeded in its design goals, and succeeded wildly. The PH-1's superb performance is right up there with its highly acclaimed phono cartridges, headphones, and the world-renowned RA-1 headphone amplifier. But despite the heavy R&D, the price of PH-1 is surprisingly light. You can pay a whole lot more and still not touch the superior sonics of the affordable PH-1.
Problems of Traditional Equalization Approaches
The breakthrough circuitry of the PH-1 doesn't rely on the time-honored methods of passive or active equalization circuits. The relative advantages and disadvantages of these old methods are very well known. The passive preamp approach is characterized by problems of first-stage headroom and second-stage noise. This is due to the 40 dB high frequency insertion-loss of the passive network itself. Phono stage gain is frequency dependent with the result of too little feedback at the low end and too much at the high end. Of course, both extremes are sonically non-optimum and unacceptable.
The more commonly used active equalization stage provides solutions to the classic passive circuit problems, but it also comes with a whole new set of problems. These difficulties arise out of the subtle ramifications of the classic negative feedback theory. The RIAA characteristic requires that the amplifier's closed-loop gain needs to change by a hundred to one (40 dB) over the entire audio range. This means too little feedback-closure at low frequencies and too much at high frequencies. Too little causes inadequate suppression of simple distortions, and too much causes the generation of complex distortions (high-order).
An Innovative Solution from Grado
The Grado phono preamp circuit design possesses all of the advantages of the old methods, yet none of its antiquated disadvantages. It relies on an equalization technique that is a derivative of the principals that Grado used in its highly regarded RA-1 headphone amplifier. The processing problem has been resolved by splitting the circuitry into two separate parts: a forward propagating signal current and a back propagating error voltage. With this design, the feedback closure ratio does not change with frequency, but the total output gain does. The end result is that virtually all latter-stage noise disappears. The output impedance is very low, with the EQ stage opened-loop and the closed-loop gain being the same, bringing analog enthusiasts the best of both worlds.
Grado's innovation is significant because its claims of technical superiority absolutely correlate to an unprecedented improvement in openness, greater depth of field, and increased definition to the sound of each musical instrument. The PH-1 offers a true freedom from past sonic problems along with Grado's usual warm, smooth, full bodied, non-fatiguing and rich sound qualities that everyone has embraced.
If your turntable is driven with a superior cartridge (including those made by Grado), then you deserve to go the final step with the PH-1 phono preamp. |