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Impressions of PS Audio GCPH

I recently obtained a PS Audio GCPH and there are a few observations of the circuitry that surprised me, in the face of the advertised information provided by PS Audio.

First, as some have mentioned in the past, the noise performance limits the actual gain you can use with this device. For example, the 48 dB gain setting is only 48 dB when the front panel gain control is maxed out (full CCW). But if you use full CCW, the noise is intolerable. In my system (Parasound JC2 line/JC1x2 power/B&W 830d) I can use a max gain of 12-1:30 on the GCPH before I can hear audible noise. That is with the input source impedance loading set to 1K (which is typical for midband MM cart impedances). Setting the loading down to 100 Ohms improves noise a bit. The noise was not all hum, but mostly white thermal noise, which means the transformer orientation inside the GCPH is OK. At the volume control setting of 1:30 (12 being straight up), I measure the gain at 40 dB with 3 mV (at 1000 Hz) in, 300 mV out. Considerably under the 48 dB stated.

Checking the other gain settings I also found that the usable gain is about 6-8 dB below the marked settings. I checked the highest gain setting of 66 dB and got about 60dB actual usable gain (.5 mV input, 500 mV out) at the 1:30 volume postition).

I think this is still high enough for most cartridges, except for really low output (150 micro-volt) MCs. Its just that the advertised and marked settings are misleading, particularly if you need the higher gains.

A word about my noise tolerance criteria. I find noise level unacceptable if I can hear anything out of the drivers (with my ear at 6") at my normal listening volume. With my CD playback system (CA 840/Bryston BDA-1) the noise level is undetectable at this same level (and to even much higher gains), so the phono preamp should be able to reproduce this as well.

The other observation I found concerning was that the actual circuitry uses two monolythic IC circuits for the preamp. The device is an Analog Devices SSM2019B pre-amp. I was under the impression that the GCPH used only "fully balanced True Class A circuits through-out" (Ryan Conway, PS audio review on Audio Advisor), meaning discrete Class A circuitry. It is not. The SSM2019B is not differential balanced, and its questionable whether it is Class A biased either. The gain cell modules appear to be output buffers.
dhl93449
michelzay
114 posts
 
I set it first at 54db and volume knob to 3:00 - 4:00, the sound with MX135 was too compressed and not too much details. As a test I changed it to 66db @1:30-2 and sounds was much more open.

Without MX135, I used also the same combination and found more details on mid to high-frequency ranges compared to 54db @2:00.

If you ask me why? I am not sure about it...
michelzay
114 posts
 
Actually, I made a mistake on writing about gain setting!! I use only 48 and 54 db at 2:00 and mot 66db!
rodman99999
6,206 posts
 
Hello again Mr D- I checked both the manual that came with my unit, and the site(url) that I posted. Both have pics of the GCPH. My manual(15-044-11-1) does not mention anything about discrete or Class A anything. I suppose the blurbsheet(url) I posted is out of date, and should be refreshed, as you mentioned. HOPEFULLY- that's simply an oversight, on their part. The issue of how much to spend on cables came up earlier. As I said; I'm using the GCPH experimentally, but- even my power cord(Zu Mother) cost me more than the unit itself. The Kimber KS-1030's and Synergistic Tricon Analogs both cost over twice the unit's price. I can't afford anything stratospheric, regarding cables, but I learned, long ago, how much difference carefully selected cables can make in a resolving system. That's especially true, if one gets to hear a lot of live music, and has for decades. I wonder what Mr M is using, with regards to cabling, and whether he might realize an improvement, with an upgrade.
dhl93449 OP
455 posts
 
Michel:

48-54 dB sound more reasonable. Remember that gain is only as registered on the gain setting when the volume control is full CW. If used at 1:30 - 2:00, its about 6 dB lower.

My comment about the input capacitance value of 100 pF comes from a direct inquiry with PS Audio. I did not confirm the actual value myself. Even if you open the unit, you cannot read the component values because they are all surface mount chip components. You need a magnifiying lupe just to see them!
dhl93449 OP
455 posts
 
Rodman:

I should have been clearer about the photos. The photo of the interior is not of the GCPH, it is the GCHA (page 4 of the manual, under "Questions and answers"). The same photo shows up if you Google the GCPH, and here:

http://hifi-unlimited.blogspot.com/2010/01/when-performance-matters-ps-audio-gcph.html

All the photos of the exterior views are correct.

The photo of the interior shows only two large filter caps, the GCPH has four clustered together. Look at the rear panel. There are only two RCAs, the GCPH has four. In the photo there are no range selection pots (because the GCHA does not have them) nor are there any balanced line out XLRs. The regulators with the heat sinks are not mounted in the same location either.This is clearly not the GCPH.

If we could post photos in the forum, I'd post the ones of my GCPH.

Looks like they removed language of Class A on the website, but they still speak of "balanced" construction throughout. Unless you listen to the video review on Audio Advisor by Ryan Conway:

http://www.youtube.com/watch?v=TGfpCj3rkVQ

The IC pre-amp (SSM2019) is cited to be "true differential input" by Analog Devices (TI), but it's not truly balanced, because it's output is single ended (not differential). So sorry, the circuit is not fully balanced throughout.

Re cables, anything that cost twice what the GCPH is worth IS stratospheric in my mind, but I have always been one to build my own stuff, including interconnects.

There is no reason for a MM input to have such a high capacitance (100 pF), given the range of what most MM cartridges need. I think they should have made it 20-30 pF to give the user more flexibility in cable selection. I think one main reason it is so high is the concern of the PS engineers for input RF rejection, and they may consider this more important than cartridge loading. I think I have read some comments relavent to this on the Graham Slee forums.
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