Phono Stages

PS Audio GCPH (Gain Cell Phono Stage)

ARTICLE INDEX

Introduction

LPs (the buzzword is "Vinyl") are in the middle of a huge resurgence, but phonograph records were always part of my audio listening. One of my goals has been to find a phono stage with a knob on the front. It's good to have aspirations in life. Even strange ones, especially strange ones.

So, what a phono stage does is take the very small voltage (as low as 0.5 mV) from a phono cartridge (the thing with the needle or stylus on it), apply an RIAA curve to it (this is basically an EQ curve that takes into account what the LP manufacturers do to keep the stylus from jumping out of the LP groove), and then amplify it to about 2 volts, which is then fed to your preamplifier.

Actually, my knob quest is becoming less of an issue because presently many albums now include a coupon to download a high quality MP3 version of the record straight from the record companies. This is one of the best developments in the music business in a long time, and it's being lead by the small record companies. However, most of my collection was recorded, pressed and sold during the time record companies used computers only for calculating executive bonuses. OK, that's overstating the case, some of my collection was pressed during the time when record companies were using computers to get access to your computer to see what was on there.

But why limit myself to MP3's or even 'CD quality'? Any sound card worth its bits will record at 88 or 96 kHz and 24 or 32 bit word depth. When you record at these levels, 'high quality MP3' is revealed as an oxymoron.

Now do you understand the knob quest? If you can remember back to when you made analog recordings on cassette, there was a meter or LED's showing green, yellow, and red, telling you when you had the input level too high, giving the tape more than it could handle (clipping) and ultimately resulting in distorted playback. The same thing happens in digital recording although the resulting distortion tends to sound far worse than that which occurred from clipping on tape. This is because analog slowly goes into distortion, while digital jumps into it abruptly. So, all digital recording software gives you a nifty equivalent of those level meters flashing on your computer screen. But, how do you adjust the level? How do you set it to the maximum possible without going over the limit? Your old cassette deck had a knob or sliders or something to adjust the level going to tape. Good luck finding something like that in the digital age. It's not possible for the digital recording software to make that adjustment, it has to deal with what you give it. So, with no adjustment possible, the recording level is determined by the gain of your phono stage.

Specifications

  • Gain: (Unbalanced): 42/48/54/60 dB
  • Gain (Balanced): 48/54/60/66 dB
  • Loading: 100/500/1k/47 kOhms
  • Output Impedance: 100 Ohms
  • Input Capacitance: @100ohms/47nF, @500ohm/10nF, @1000ohms/4.7nF, @47kohms/100pF
  • Dimensions: 3" H x 8.5" W x 15.5" D
  • Weight: 5 Pounds
  • MSRP: $995 USA
  • PS Audio

As long as that gain is low enough, you'll have no clipping. But at the same time, if that level is lower than it has to be, you are throwing away bits. If 16 bits at 44.1 kHz is barely adequate for digital reproduction (and it's generous to say that it is), what about 14 bits? Or 12? That is what you are getting when the amplitude of the incoming signal is smaller than the maximum line level, i.e., the quieter parts of the music.

The modern solution to this problem is to simply reset the level of the recorded signal after the fact with software. Recording software can scan the entire sample (song), find the highest level and make that equivalent to 16 bits. Every other sample will be scaled by the same amount. This creates a recording of the input signal at the highest level possible without clipping.

In reality, you've created a bad approximation of the input signal. This recalculation of every sample in the stream is a HACK that distorts in evil ways. My theory is that this kind of hubris with recorded digital signals is at the root of digital fatigue that has plagued CD playback. Compression (increasing the level of quieter or background sounds and reducing the loud passages) performed in the digital realm is the same exercise multiplied.

PS Audio to the Rescue

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So at last I have found the PS-Audio GCPH. The GC stands for 'Gain Cell' a small signal gain stage that PS Audio uses throughout their product line. If you've got a good thing going, why change it? In the GCPH, each channel has two Gain Cells wrapped around a passive RIAA equalization circuit. Each Gain Cell has adjustable gain. The first is adjusted through a four position switch on the back of the unit – 48, 54, 60 and 66 dB. The gain of the second cell is set via the knob on the front.

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The comprehensive and unusually informative GCPH user's manual recommends finding a combination of settings for your cartridge that results in the front knob being at ½ to ¾ of its range for typical listening. Driving any amplifier at 100% would result in more distortion than at lower levels. The front knob is not an attenuator, but is an actual gain control for the front GC. Nonetheless, it has sufficient range that PS Audio states that it can be used as the only volume control in a preamplifier-less system with the GCPH connected directly to a power amplifier. I tried GCPH this way in my second system - with only my computer's sound card in between the GCPH and an old NAD amp - and using the 'volume control' took the level from zero to moderately loud. Not quite loud enough to be considered 'cranking it, but listenable.

This is my second system, with an old Denon DP-62L turntable, and an equally experienced NAD AV-716, JM Lab Chorus 816 speakers, and a CardDeluxe from Digital Audio Labs. In this system, the GCPH is the star; the rest of the system doesn't have enough horse power to reveal all that the GCPH is capable of.

I know that because I mainly used the GCPH in my main system (details below). Here, I was glad to be able to take advantage of the balanced outputs into my SimAudio 5.3 Preamp. The GCPH smartly has both balanced and unbalanced outputs.


The Sound

My reference phono stage is from a kit (the Pearl) promoted by the Pass Labs DIY web site. As is the bent of Nelson Pass, this design features a single ended, single transistor gain stage. I haven't the means to measure what types of distortion might come from this sort of design but we can presume a fair amount of the second order harmonic. This is thought to be a good thing by some. I certainly am enamored with this phono stage.

The GCPH had a distinctly different sound that I would attribute to the absence of such a distortion. Indeed, balanced circuits reduce even-ordered harmonic distortion. So coming from this reference my initial impression of the GCPH was that it was on the bright side, perhaps a little brash even. This is the kind of thing that could mellow after a break-in period, but I was not expecting much of a break-in since the unit I was using was a well travelled review sample. And in fact, I did not detect too much change after a couple of weeks of listening. After a time, I placed three Boston Audio TuneBlocks underneath the GCPH. and PS Audio's user's manual recommends careful placement as well as aftermarket vibration isolation such as that provided by Boston Audio. The difference was not slight, not subtle, and not unwelcome. Gone was any hint of harshness or excessive brightness. The sound opened up remarkably. Treble still seemed to be the specialty of the GCPH, but only in that it sounded great. The soundstage was more forward than with my reference. Bass was tight and controlled and tuneful, although I'm not sure it reached the same depths of absolute gravity as with the Pearl. I kept this arrangement for the rest of my listening in my main system.

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I'm starting to wonder if it's possible to figure out what sorts of hi-fi equipment manufacturers are listening to as they voice their products. If I had to guess, I'd say that the folks at PS Audio are favoring Jazz. Trumpets, snare drums, pianos were all stellar through the GCPH, as were women's voices.

My reference phono stage prefers the lower frequencies and is more laid back. One of my favorite songs ever is Massive Attack's "Tear Drop", with melt-in-you-mind vocals from the incomparable Elizabeth Fraser (Cocteau Twins). With about half of the melody occurring below 40 Hz its great for repeated listening and great for comparing bass in audio equipment. With my reference, there was a bit more 'thunder', and with the GCPH there was more articulation of those deep notes, and the brilliance of Massive Attack's mixing board fiddling was more evident.

However, the more I listened to the GCPH, the less difference I heard between the two phono stages, I attribute this more to my ears breaking in than the GCPH because this particular unit has been well traveled. The control and authority of the GCPH really grew on me over time and as should be expected with vinyl, without a hint of fatigue (if I want fatigue I listen to CD's).

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Boston Audio makes a variety of vibration isolation products from carbon graphite (not fiber). For this review I tried the MAT1, a record mat replacement for most any turntable, and I also got some TuneBlocks which are cylinders made of the same stuff, designed to be placed under components. I tried the TuneBlocks Series 2 XT which are cylinders 2" in diameter and 1.5" high. In addition, the XT's have a recessed cup, about ½" diameter, carved into the top to hold a small ball bearing. Here is where the component rests. This height can be a little off-putting, as the GCPH on TuneBlocks looks a little bit like a monster truck, raised too high for its own good.

Besides the aesthetics, there's the issue of macro stability to think about. Will your component roll away when placed on the TuneBlocks? The recessed cup for the ball bearing means it's not going to roll very far. I tried pushing the GCPH in the horizontal direction while it was on blocks as it were, and the feeling was similar to pushing on foam. The ball bearings would roll only a small amount before hitting resistance as they tried to roll up the side of the cup. However, the GCPH was not as stable in the horizontal direction as it would have been standing on its own feet, or some sort of spikes. The ball bearings are not at all sticky, and if I kept pushing, the GCPH would simply slide along the top of them. This is not anything that concerns me, but if you or a pet or some other creature were to bump a Tuneblock-suspended component, it would move a more than if it were on rubber feet.

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Since replacing the mat on a turntable is about the easiest audio equipment installation imaginable, I tried the MAT1 first. Replacing the foam (read 'cheap foam') mat that came standard with my Nottingham Space Deck and still using my reference phono stage while the TuneBlocks and GCPH were safely tucked away in their boxes. There was an immediate improvement; all tones from bass to treble were more clear, less muddled, especially treble. And I didn't think there was any muddling before. The effect was not subtle and it was entirely enjoyable.

Usually, when someone describes an audio improvement as 'clarity' the thing to watch out for is 'grain', that etched, annoying quality most evident these days in cheap CD players but also found in playback from turntables that suffer from vibration problems – such as a direct drive turntable. Replacing the standard soft foam that came with the Nottingham with the stiff MAT1 had me worrying that some grain, some vibration that was formally absorbed by this foam would now be revealed. I worry no more. In fact, I didn't even think of the word 'grain' until I started to write this review. I could not discern any tradeoffs in going to the MAT1.


I left the MAT1 in place and enjoyed many records that led to the opinions expressed above. When it came time to finish this review, I picked a well recorded piece of overly priced, 180 gram, virgin vinyl to do some comparisons with: David Gilmour's On an Island. Portland, Oregon is blessed with several still-going-strong independent record stores. However, the strongest, Music Millennium, recently had to close one of its two stores. This seemed to have more to do with the landlord getting dollar signs in his eyes during the recent real-estate bubble than a lack of business in the store. The bright side for local vinyl junkies was the 40% off closeout sale. So, Mr. Gilmour's latest offering cost me 'only' 24 dollars. At this price at least, it was worth it. As long as I'm playing it on the MAT1 I should say. With the standard foam the sound was congested and closed in, and I kept looking at my turntable trying to think of ways to better isolate it from vibrations because there must be something that needs fixing over there. When I put the MAT1 back on, instruments had proper attack again, the steady strummed bass in the opening track "Castellorizon" had texture again, the top end was open again, and voices, instruments, and drums were all separate. Rhythm and pace were also improved.

What should the material be? What did they use when they engraved the record? Metal backing wax I suppose. Is that somehow equivalent to felt or foam or solid carbon underneath vinyl? Where's a mechanical engineer when you need one? I suspect, as the MAT1 web site points out, the choice made by turntable manufactures has more to do with economics than engineering. It's interesting to note that Nottingham ships a graphite mat standard on its higher end turntables.

Note by Editor: The reason that reducing the low frequency rumble that some turntables have is so important is that it can interact with other frequencies and cause IM distortion, which can make things sound mushy.

Conclusions

Everything you've read about above is now mine, I'm buying it, they can't have it back. In fact, I have to get a second MAT1 because I tried it in my second system, with the Denon DP-62L which is a direct drive turntable. Here I was thinking that I would have to replace this lovely old-school table because the grain from the direct drive system defeated the purpose of recording from vinyl. Turns out the problem was the rubber mat. The second song on the second side of Radiohead's "In Rainbows" sounds like Radiohead meets Low meets Sigor Ros. Through headphones without the MAT1, I was waiting for it to be over, I switched to the MAT1, and the haunting vocals are still in my head a week later.

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