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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
438 posts
 
Swanny:

I'm just getting back into vinyl (after 30+ years), so this is a "starter" phono preamp for me. I use Parasound line (JC2) and power (JC1) amps and up till now have only had CD sources (CA 840C with a Bryston BDA-1 D/A).

I considered the Parasound JC3 phono, but its 2.5x the cost of the PS Audio and I did not want to commit to that much cash at the beginning. The Parasound is also quite inflexible in cart loading choices, and gain is fixed as well.

My only beef with the GCPH so far is the cap loading (it is fixed at each resistance loading position); also it is too high for some MM carts (like the AT 150 MXL), forcing you to buy very expensive phono interconnects. Some of these cost as much as the GCPH itself. With MCs, this is much less of an issue.

My other concern was I thought this was an all class A discrete design, which it is not. Not to say that having an IC amp input circuit is a bad thing (in fact it is quite common in phono pre-amps under $1000), but their advertising implies otherwise.

I also considered the CA 650/651 products, but they need considerable modification for best sound quality. They are considerably cheaper however.

I am also considering a modification to the GCPH to remove the torrodial transformer and relocate it in an outside chassis, perhaps even building a DC supply with it and running seperate power into the GCPH. This would do a lot to reduce the noise floor even further, as I could easily see the 60/120/240 Hz power artifacts in the spectrum analysis.
dhl93449 OP
438 posts
 
Had more time to investigate the noise issues and found that the large filter caps in the power supply were not soldered well to the PCB. PS Audio uses plated through holes as part of the signal path and the copper in these holes (that mount the filter caps) seemed to be defective, as the signal was not connecting well from the lower traces to the upper traces. I soldered a heavy jumper wire to enhance the connection and what will you know, the 120 Hz noise level dropped dramatically.

I am looking next into relocating the torroidal transformer to an external chassis.
rodman99999
3,557 posts
 
I've experienced no noise problems at all with the GCPH. That's set at it's highest gains, inputting a Dynavector 17D3(.3mV output), with SR's Tricon Analog phono leads. I run my TacT 2.2X at 99.9 and use the GCPH volume control, which is generally close to maxed(the 2.2 contributes very little gain), or maxed with some albums, recorded at lower levels. Only after 2:00 on the volume knob, do I start to hear a slight 60Hz hum(none- with the phono leads disconnected, and I am extremely sensitive to extraneous noise). I've simply been experimenting with the unit, not expecting much from one so inexpensive, to find what loading and gain I needed, with my system and low output cartridges(17D3 and Denon 103D). I intended to install FREDs, but found fairly fast diodes in the unit already. A HI-FI Tuning Supreme and Zu Mother PC, made a marked difference in the presentation. Defects do occur, regardless of manufacturing procedures(especially when humans are involved). I'd have sent the unit back, and let them find the problem, once I eliminated every other possible noise source. I was dismayed, to find that the thing was manufactured in China. A fact NOT mentioned in ANY of PS Audio's ads, or in any articles written on the piece. No surprise that your problems were not caught by Quality Control(AS IF that existed there)!
dhl93449 OP
438 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
3,557 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!
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