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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
 
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.
michelzay
114 posts
 
Sorry for these 2-3 weeks of delay on reply, I was out of country for a conference back in EU.

DHL93449, Glad to hear that you did successfully relocate power transformer outside of the Box and you are happy with results. BTW I do appreciate that you took time time to look at MX135 Manuel, thanks a lot.

To answer you question, yes, earlier I did try to use BAL1 of MX135 input (used for CD player) for GCPH and still had the same problem of sound degradation. I used other type of cables too, but not a big improvement!

I also looked at the internal circuitry of MX135, to find out how to bypass pre-amp stage and lead gcph signal directly toward MX135 output. In schematic MM phono goes through a first stage pre-amp, along with other inputs (RCA), it gets buffered before switching stage with Balance inputs. Selected input after another amplification stage goes to the processor where as an option one could choose external inputs too, without these pre-amp stages fed to the processor. Output of processor gets treated for Bass/TREB boosting options before final stage. Therefore, I tried different configurations to ameliorate sound quality of GCPH+MX135 and the result was not really encouraging!

This last weekend, I took my GCPH with some selected LPs to a friend’s house and tried to test it on his hi-fi system (Roksan Xerxes, AQVOX phono, Krell 280, krell PFB250s, Focal Diva speakers). We made some experiments with Krell-280 pre-amp, ps-Audio GCPH, AQVOX phono and different cartridges (MM/MC). Issue concerning gcph+preamp sound degradations was present but a little bit less audible; I mean Krell 280 compared with MX135. Again, GCPH + AMP were much better in sound quality. I have to say AQVOX phono was phenomenal! AQVOX phono+pre-amp were excellent and AQVOX+AMP were even better! There were some differences but not really very audible. We also tried different phono cartridges and compared related quality of GCPH and AQVOX phono. AQVOX outperforms GCPH in details especially in fastness and imaging aspects, as well as different range of frequency, better midrange, and higher freqs with a bass deeper than gcph.

I brought home for a couple of days the AQVOX and made some test with my MX135 and my new JA MICHELLE Gyro turntable. AQVOX+MX135 present an excellent sound, much better than GCPH+MX135. In case of AQVOX+AMP I got same sound quality with deeper bass. With AQVOX, I got much more details in sound compared to GCPH. The MM phono stage of AQVOX is as good as MX135 phono stage where I got a little bit more forward sound with MX135.

As for different cartridges, MM cartridges in GCPH present reasonable sound quality but with LO MC GCPH couldn’t handle it properly. I used MC cartridges too, where I found out MCs with an output of >0.45mv should be fine but with very LO MCs the degradation is really audible. Contrary to PS-audio GCPH, AQVOX is perfectly capable to handle even very LO MCs. Unfortunately, in PS-audio manual/specification it doesn’t provide any information on min/max input sensitivity for MM or MC cartridges!!???! It is bizarre …

Once again, I checked reviews on GCPH, nobody mentioned quality differences between GCPH W/Wo external pre-amp because they didn’t perform these sorts of tests. I also asked a ps–audio dealer in SF area and they didn’t have any experience on this regard!?

Based on my experience with both AQVOX phono and ps-audio gcph, I would certainly recommend AQVOX phono with a price tag of 998.00 Euro~$1250. It could handle very LO MC (>0.15mv) and it is totally configurable for different phono cartridges. It could be purchased only online from Germany website which might be inconvenient for some people!!? I wish I had purchased AQVOX instead of GCPH.

Being frustrated with GCPH experience, I decided to disconnect my ps-audio gcph from the system and will use only MX135 with its MM phono which is excellent, until I purchase a MCintosh MC2300, having both MC/MM phono stages. It is sad but that’s my fault to not have tested gcph before, and just trusted the reviews …
dhl93449 OP
455 posts
 
Michel:

Maybe you have a problem in the GCPH? If it's still under a warranty (and even if not, PS Audio is very liberal with potential warranty issues), I would contact PS Audio and explain your situation. I would think that maybe you have a problem in those gain cells. Can't hurt to send to PS Audio for a check up. If they say it's OK, then just consider selling it.
michelzay
114 posts
 
Mr D.,

Yes, It is a new device!!! 4 weeks ago I contacted PS-audio and someone named MArk, after a few exchange messages , suggested that he will find a dealer that I could take my GCPH there and eventually use different cables or loan me some cables and ... since then I didn't have any feedback from them!!?!

If there is an internal circuitry issue with my ps-audio it would be so shameful for Ps-audo that they don't have a quality check line on their products!

My guess is that the problem is the overall quality of GCPH which is on question, some people find it perhaps reasonalbe quality for $1000! I am not sure ... Honestly speaking that is a lot of money! that's why I expected a high quality sound out of it ... and that's why I am disappointed ...
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