Phono Amp

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Phono Amp REVIEW

AUDIOPHILE AUDITION
Grado Model PH-1 Phono Preamp
By John Sunier

INTRO

It might seem odd that with only three component reviews per month this is the third phono preamp review in the last nine months or so. The reason stems from my moving from separate audio and home theatre setups to a single all-in-one system, and from a tubed "hairshirt" preamp with all sorts of phono preamp options to a complex AV surround preamp which has only a so so moving magnet input. I presently use a moving coil-the transfiguration Spirit cartridge. And added to the equipment change was a serious problem with both hum and RF interference that I experienced once I hooked up in their final resting place both of the previously-reviewed phono preamps. One of the local rock FM stations bombed in whenever there was no signal from my turntable. Changing the various cables made little difference, and driving a copper post into the ground and running a ground wire inside to the equipment only made the hum worse.

The last cable change I made was to replace the 1 meter Cardas turntable to-phono preamp cable with a .5 meter. Even when wrapped with two layers of aluminum foil the previous cable still acted like an antenna for the pesky rock station, but the new cable was an improvement even without the foil wrapping. Next I began a search for a less sensitive and more hum-free phono preamp-hopefully one without the high cost of some of the latest and greatest out there such as the Manly.

One of my first site visits was Grado Labs. Some years back I had reviewed their terrific little wooden box RA-1 headphone amplifier, which was battery powered. It was the best ­sounding headphone amp for Grado phones, hands down. At their present web site I learned about the model PH-1, which turns out to be a derivative of some design principles use in the RA-1 headphone amp. The appearance of the new unit is even similar, with a small red LED on the front of the wood box. However, the phono unit is AC powered rather than battery.

THE CHALLENGE

According to the Grado folks the technical challenges of designing this preamp were the biggest undertaking they had ever engaged in. They wanted to build a superb-sounding phono preamp to work with both MC and MM cartridges, both low-output and high-output, and with negligitable noise. Ultra-wide bandpass, high overload, virtually perfect RIAA amplitude and phase coherence, and very low output impedance were other goals they set out for themselves. They didn't want to go the passive preamp route because of the problems with of insufficient headroom in the first stage and noise in the second stage. They pinned this problem on the passive network itself causing a 40db high frequency insertion loss.

They also felt that active phono equalization had its own set of problems arising from classic negative feedback theory. The amps closed-loop gain needs to change by 40db over the entire audio range to meet the required RIAA characteristic. This means too little feedback-closure at the low frequencies and too much at the high frequencies-resulting in serious distortions. Grado Labs feels that they have solved the problem in the PH-1 and kept the advantage of the old methods with none of the disadvantages. There are two parts to the processing circuit-a forward-propagating signal current and a back-propagating error voltage The feedback closure ratio does not change with frequency, but the output gain does. Thus virtually all latter-stage noise disappears and the output impedance is very low.

THE LISTENING

The very first thing I noticed after hooking up the PH-1 was that it is so small that it could be placed directly under my Sota turntable with room to spare. This meant that I could go from a 1meter cable to only a half meter and reduce by half the pick up area for the FM RF interference. It magically solved both my hum and RF problems in one fell swoop.

After letting it warm up a couple days and during that time demagnetizing my Transfiguring cartridge, I started in with some listening tests. I set the level switch to the 56db setting for my low-output MC. I used the unit to review all 16 new vinyl releases reviewing in last month's issue. The rich and open sonics I got from everything were a joy to hear. Some of the classic Records reissues which a few months before had sounded almost exactly like the xrod digital reissues of the same performances, now possessed a subtle edge on the CD versions. There was more openness and "air" around the instruments that even on the very best xrod transfers was missing. And on some comparisons in which the xrods had the superior low bass extension, the bass frequency playback now seemed just about the same and on occasion even more extended on the vinyl. There was also an improved depth of field on many LPs, even on those in the "deep mono" area - such as the wonderful Count Basie mono reissue from Classic. While I didn't any longer have around the top-rated Linn Linto preamp, I felt my long-term memory was good enough to grok that my personal taste leaned toward the richer and warmer sound of the Grado preamp.

WRAP UP

I'm happy as a clam with my PH-1, and not only because it provided an instant solution to months of struggle with my hum and RF problems. It seems to have nothing but excellent qualities with no fuss or bother, a beautiful and compact little box that can be placed most anywhere without picking up hum or noise, and at a cost that seems miniscule compared to the highest rated phono preamps that have unexpectedly appeared on the scene in the last couple of years. That little red LED under my turntable is a cool addition to the array of LEDs in my listening room. The Grado dedicated headphone amp sounded best by far with Grado headphones, and although the PH-1 sounds terrific with my non Grado MC, I'm going to give it a run later on with Grado's moving-magnet reference cartridge and see if that combination is synergistic enough to wean me from several decades of moving-coildom.

Phono Amp

THE GRADO PHONO PRE-AMPLIFIER

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.

Happy Listening!