Grado's New Proprietary Phono Equalization is "The Best of Both Worlds."
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 more commonly used active equalization stage provides solutions
to the classic passive circuit problems, but it also comes with a whole
new set of its own 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 (40dB) 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).
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!
What is so significant about these new innovations is the fact that
the technical superiority claims 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 Grado cartridge then you deserve to go the final step with the new PH-1 phono preamp.
