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

ps-audio-gcph-fig-2.jpg

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.

ps-audio-gcph-fig-3.jpg

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.