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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
dhl93449 OP
455 posts
 
Rodman;

Thanks for your comments. After re-soldering the caps the audible noise (60-120 Hz) was reduced considerably, although my measurements were made prior to this. So I doubt if PS Audio would would say there is anything wrong, as the specifications were pretty good as measured, and I have no published specs to compare (and I don't know what internal specs PS Audio uses). So you may have a unit that was soldered well from the getgo.

I still cannot use the volume control past about 1:30, but that is OK because I can get all the gain I need with the rear gain control. I am planning on using an AT 150 xlm MM cartridge, but attenuated by 5:1 (see my post under Analog). With this setup at 66 dB gain, AND the phono interconnects/tonearm/cart connected, the noise level is extremely low, with little to no hum detectable with my ear at the speakers, and my normal max gain settings.

The made in China issue is a fact of life today, but what frosted me to some extent is the comment I made previously, where PS Audio claims the GCPH contains "all balanced class A circuitry" which it does not. It uses an IC pre-amp which is neither balanced or class A. I'm sure they were refering to the Gain Cells, but they should know better when trying to market to audiophiles.

I do not know where in China the GCPH is made, but if it's Taiwan (as opposed to Mainland) that's about as good as it gets. The most sophisticated electronic products (such as motherboards and video cards for PCs) are made there. Quality issues (or lack thereof) are typically produced by corporate bean counters looking to cut costs, as opposed to where something is manufactured.

And regarding the relocation of the transformer, I cannot see how this would not reduce hum levels even further. Mounting that torrodial transformer within INCHES of the low level circuitry, without any shielding, seems to be too much of a design/cost compromise to me. I know the noise can be minimized by rotating the transformer, but come on, why not get the thing out of the chassis altogether? I asked this question of the PS Audio marketing folks and the answer was a simple one word "cost".
rodman99999
6,206 posts
 
I agree, regarding the X-former location. Ideally; the entire power supply would be in a separate chassis, but- we ARE talking about a sub-K unit here. I know that discrete use of TI's EMI/RFI shielding can make a marked difference, within the unit. PS Audio makes this statement about their gain stages: "The GCPH is built around two discrete and fully class A balanced gain stages: a high gain, low noise input stage and a Gain Cell for the output stage, with the passive RIAA curve between the two stages." They DO say that the unit is a, "true balanced design from input to output", but don't claim it to be Class A, all the way: (http://www.psaudio.com/products/audio/perfectwave-accessories/gcph-phono/). I believe PS recently moved all their manufacturing back to this side of the pond. I'm certain yours was not the only problem unit produced over there. As far as marketing to them: Given the technical ignorance of the average, "audiophile".....Well, have you ever read the crap/hype printed in an 'Audio Advisor' brochure? Happy listening!
dhl93449 OP
455 posts
 
Rodman:
The GCPH description "built around two discrete and fully class A balanced gain stages: a high gain, low noise input stage and a Gain Cell for the output stage, with the passive RIAA curve between the two stages" is what is no longer true. The "low noise" input stage is an Analog Devices SSM2019 "Self contained Audio Preamplifier", not discrete circuitry. Maybe the GCPH was at one time, when the marketing hype was written, but not in the one I received. Like most IC OP amps, its biasing state (Class A or otherwise) for all the internal gain stages is unknown. So to claim it's "Class A" is stretching the truth somewhat. And, the SSM2019 is not "fully balanced", its single ended, as a quick review of the AD data sheet will reveal.

I have no issue with PS Audio improving their products and maybe the SSM2019 is an improvement over discrete stages (or maybe discrete low noise transistors are becoming impossible to find any longer), but their literature should be updated to reflect what they are currently selling, not what they designed 10 years ago. Did you also realize the photos of the product in the manual and online are not of the GCPH, but the GCHA (the headphone amplifier)?

There are a number of sub 1K phono preamps that have outboard transformers (maybe not full DC supplies). I agree that these mostly are cheesy wall warts and not the beefy 50W torodial transformer PS uses. I am putting together a kit to relocate the PS transformer and build a remote DC supply for the GCPH.

Yes, I have received "advice" from Audio Advisor. Not all that accurate and we can leave it at that.
michelzay
114 posts
 
Hi there,

I purchased a new PS GCPH a while ago for MC cartridge usage and just used it in my system, which consist of a Mcintosh Mx-135, Denon Dp-A100 TT, Mcintosh MC402 and B&W 804d.

1. When I use ps gcph+amplifier, without another pre-amp, the sound is fine, but the MX135 with its MM is much better!
2. In connection mode “without PS gcph”, Denon DP-A100 (TT)->MX-135->MC402, the whole system sounds wonderful with MM cartridge (AT440ML). However when I put PS GCPH into the chain such as, Denon DP-A100 -> PS GCPH ->MX-135->MC402, the sound quality degrades enormously and gets lean where I loose some details such as imaging, staging, edges on Bass and midrange frqs. I still didn’t try MC cartridges with PS gcph+preamp but I guess I will have the same effect.

As a matter of practicality of using one main cable set with my amp and not switch it between Ps gcpj and pre-amp, I was wondering why using PS gcph+preamp degrades the sound enormously and what should I do to gain the sound quality that I would expect from ps gcph?

As for input level informations on MX135, here is the data:

Input Impedance
Phono: 47k Ohms, 65pf
High Level: 22k Ohms Unbalanced
50k Ohms Balanced

Sensitivity for inout
Phono: 5mV
High Level: 400mV Unbalanced
1V Balanced

Maximum Input Signal
Phono: 50mV
High Level: 5V Unbalanced
10V Balanced

I would appreciate your feedback. I tried PS audio support desk and so far there is no result!?!
dhl93449 OP
455 posts
 
I suspect the input capacitance of the GCPH plus your phono cables is too high for that cartridge, but that is just a guess. Its not published, but PS told me the input capacitance for the MM/47K input is 100 pF. I have an AT 150 MLX that requires a max of 150-200 pF, and is reported to sound bright and edgy with higher capacitance. 150 pF is reported to be the optimum, but with the GCPH 47K input of 100 pF and an arm wiring capacitance of 30 pF, it leaves only 20 pF for the cables. Almost impossible to obtain (unless you want to pay thousands for the interconnects).

The Mac may sound better because it has a much lower input capacitance at 65 pF.

In my case (see my post under analog on the AT 150) I solved my problem but using a 5:1 attenuator ahead of the MM input on the GCPH. This isolates the 100 pF input cap from the cartridge, and now I can use 100-120 pF cables without exceeding the 150 pF loading on the cartridge.
I use a gain setting on the GCPH of 60 dB to compensate for the attenuator.

The attenuator is easy to build. Its located in an inline RCA adapter that plugs into the GCPH inputs.
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