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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:

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.
michelzay
114 posts
 
Regarding Cables used in my system, I initially used AQ king Cobra, and switched to AQ Columbia, AQ Niagara and Nordost Heimdall. Of course there has been some improvement on sound quality when signal goes directly to AMP. The sound is pretty good and I like it very much so. This scenario is kind of not practical because when I want to listen to CDs I need to disconnect cables from GCPH-AMP and reconnect it again to my pre-amp(MX135)!

Unfortunately, the problem of sound degradation is being present once I use GCPH+pre-AMP+AMP. Even though using my AT33 cartridge, it sounds worse than a cheap cartridge as $20, no details at all on output sound ... I guess there is a mismatch (capacitor/impedance) between these two and I am very curious to find how?

Mr Rodman, I totally agree that cables play a huge role on sound quality, but I am afraid this case is not directly associated to cable issue. In case of upgrading cables to $4k cables only on phono stage, I would rather to buy a Manley Steelhead phono pre-amp, or the most practical option would be to upgrade to MC2300 where its phono stage is so phenomenal.

I read in these comments that you guy use gcph with some other pre-amps like parasound, TAcT and ... I was wondering whether how was your experience on using GCPH with pre-amp and how would you compare sound quality on GCPH+AMP and GCPH+pre-amp+AMP?
dhl93449 OP
455 posts
 
Michelzay:

In most of the research I did before purchasing the GCPH, I found no sources that really found the sound quality unpleasant or unsatisfactory. Noise/hum were common complaints in earlier reviews, but never sound quality. I am still in the process of building my phono setup, so I have no direct audio performance to report other than the noise issues mentioned above.

I do find it strange that the GCPH in your system sounds good when connected directly to your power amp, but not to the same power amp thru the MAC line amp (pre-amp). That would indicate to me that there is an issue with the line stages in the Mac pre-amp, either a voltage overload issue or maybe an impedance issue (as you suggest). I doubt if it's cables, as I would assume you use the same cables to connect to the power amp. I am also assuming the power amp has similar impedance/voltage requirements as the Mac pre-amp.

I would try backing off the gain in the GCPH and see if that does not improve things. Also, try different Aux line inputs if they are available. I know my Parasound P3 had different quality amplifiers connected to the different inputs. Maybe that's the case with yours as well. If not, maybe you need to move on to another product.
dhl93449 OP
455 posts
 
Michel:
I took a look at the specs for your Mac pre-amp. I did not realize it was a large and complex AV pre-amp.

It very likely uses operational amplifiers (IC op amps) for those miriad of inputs. The spec I saw showed it did not have a phono pre-amp input, but maybe yours is different. It would not surprise me that the GCPH directly into the power amp will sound much better than going into the line inputs of this AV pre-amp and then into the power amp. You are cutting out a lot of intermediate processing and amplifier stages. Perhaps the phono input stage of this AV pre-amp is designed to bypass some of that processing as well. Also, if op amps are being used, you definitely want to keep your input voltages as low as possible, as the distortion performance of many types of op-amps increases dramatically once you get near 1 volt (even though their spec sheets won't indicate this).

Are you using the balanced inputs or single ended? In some amps, they sound different so try both.

Also, if your CD sounds good to you, I would try inputing the GCPH into the same CD input for comparison. Adjust the volume on the GCPH so that it matches the volume of the CD deck and make the comparison.

But in general, I would not expect you will get sonic parity by putting the AV pre-amp between the GCPH and the power amp.
dhl93449 OP
455 posts
 
I have completed my project to relocate (or actually disable) the power transformer for the GCPH.

I built an outboard power supply with a similar torroidal transformer and 132,000 mfd of power supply capacitance, and disconnected the stock torroidal transformer. The DC inputs go into the bridge diodes via the same connector the original transformer was connected to. I left the original in place in case I want to go back to stock.

The results are amazing. All audible hum components in the output are GONE. No hum whatsoever. On any gain setting, all the way up to max volume. I am very pleased with these results.
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