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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
 
nipplewhatever:

Visiting this post after a few years.

Your comments are just stupid, as you did not read carefully what I was saying. When you measure the noise of a preamp (which is what I was clearly doing), you user the source impedance of the cartridge NOT the input impedance of the preamp. I was correct, most MM carts have a source impedance around 1K (at low frequencies), not 47K. Since thermal noise is strongly dependent of the level of the resistance, 1K will produce lower thermal noise than 47K, and 100 ohm is even lower. All of which I clearly stated. And most manufacturers, in PS Audio, measure noise of their product with the input SHORTED, or 0 ohms, to get the best noise specs. I was trying to get a real world noise measurement by using 1K.

Next time read what I say before you jump and open you big mouth. 


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markshvarts
32 posts
 
dhl93449

Hi. I have just bought the GCPH, and having the same issues as you did - hum. Since the unit sounds pretty good otherwise, I was wondering if you could help me with fixing the noise issue. I’m pretty handy with soldering iron, pretty sure I can relocate the transformer, but don’t mind getting it moded by you. I read elsewhere that location of filter caps and diodes is also not so good, too close to audio circuit… Thank you. 
rodman99999
6,123 posts
 
@markschvarts-  Are you experiencing that hum, with the input cables both attached and detached?

      If detached: at what position of the dial, does it become audible?

      If anything below full volume (or thereabouts); I'd contact PS and request a checkup.

"I read elsewhere that location of filter caps and diodes is also not so good, too close to audio circuit..."

      Removing everything in the power supply and returning nothing but DC, to the GCPH’s chassis, WOULD be the hot setup.

      Subsequent my last post: I did replace the diodes with HEX-FREDs and the regulators with Bellesons, in addition to the afore mentioned mods.   A marked improvement.  BUT: that’s referring to overall sound quality and not noise, of which I’d had none.   Except: when trying to get a lot of gain, with low output MCs (Denon 103-d and Dynavector 17D3, .25mV and .30mV outputs, respectively).
coltrane1's avatar
coltrane1
739 posts
 
GCPH user still in 2021. It’s connected to an integrated. No noise, no hum, simply great music. Did I get an improved one? I don’t think so. PS Audio sold thousands of these most of which are still circulating and being used today, even though there are far cheaper phono preamps sold today. I paid $400 used for this one. I couldn’t be happier with its performance.  
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