Grado PH-1 Phono Stage

Our new Grado Phono Preamp, model PH-1, represents the most successful solution to one of the most complex technical challenges in the field of audio that Grado Labs has ever tackled. It can be compared to the undertaking of designing our highly acclaimed phono cartridges, headphones and our world renowned RA-1 headphone amplifier over the past several years. Our design goals were for a truly superb sounding phono preamp to work equally well with both low and high output cartridges with negligible noise. We wanted a phono preamp with ultra wide band pass, high overload, virtually perfect RIAA amplitude and phase coherency, and very low output impedance. This was the challenge set forth! This we have accomplished!
We realized immediately that a challenge like this was not going to be met by using either of 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 40dB 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 new Grado phono preamp circuit design now has all of the advantages of the old methods, yet none of its antiquated disadvantages! The challenge was met! The processing problem has been split into two separate parts: a forward propagating signal current and a back propagating error voltage. We have indeed eliminated all of the past methods. Our new phono equalization technique is a derivative of the principals that we used in our highly regarded RA-1 headphone amplifier. In this design, feedback closure ratio does not change with frequency, but the total output gain does. 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. The best of both worlds!

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