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. |
Swanny:
No, I was using the single ended outputs. I am not sure about the 6 dB more gain beacuse it depends on how the line pre-amp handles balanced inputs. Uncertain about the JC2, but some pre-amps I know of divide back the 6 dB gain when they convert back to single ended internally, so they match the same levels of other singel ended inputs.
Since my original posting I had a chance to make some measurements on a spectrum analyzer. I thought I might have a defective unit. Although PS Audio does not publish noise specifications, I thought I might compare it's performance with some other products (such as the Cambridge Audio 651, which has some pretty good noise specs).
What I found was the noise performance is pretty good. At the x48 dB gain position, I got a noise level of -105 (200 Hz) to -110 (20 KHz) dBV (ref to 1 V RMS output) at the 1:30 volume positition, or 40 dB actual gain. Moving the front volume control to MAX CW position, gain is x48 dB, and noise increases to -90@200 to -100@20K dBV, which tends to indicate you are picking up a bit more noise than you are gaining in gain. These measurements were made with the internal 1 K source resistance (not shorted), which is more realistic source impedance of a MM cart. These are raw measurements, with no weighting (A or C). The range of about -10 dBV indicates the drop in noise with frequency from about 200 Hz to 20 KHz.
At the 66 dB gain position, I measured noise levels at the 1:30 volume position (actual gain of 60 dB) to be essentially the same as the x48 dB gain setting; -90 to -100 dBV. But increasing the volume to MAX, noise increased to -75 dB (200 Hz) to -90 dB @ 20KHz. Source resistance was 100 ohms. Here you lose a wopping 15 dB SN for an increase in gain of only 6 dB.
So at x66 dB, MAX volume, you get a worse case noise level of -75 dB, un weighted, which is pretty good. Weighting and shorted inputs always improve the numbers somewhat. But -75 db is pretty audible based on my earlier criteria of listening to the drivers directly. The SN in my system is worse than -75 dB because my gain is set for a listening level ref to 300 mV, not 1 VRMS (which is now actually -65 dB ref 300 mV RMS).
So with the GCPH, if you need gain use the main gain switches at the back, and try to keep the volume control at 1:30 or below. |
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. |
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. |
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". |
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.
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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. |
Michelzay:
Forgot to ask, what inputs are you plugging the GCPH into when you use TT>GCPH>MX135? A high level Aux input, right? The same one you use when you use a MC cartridge with the GCPH?
You of course cannot connect the GCPH into the phono stage of your MAC pre-amp. That would be disasterous (you are double RIAA EQing!)
If you are going into an AUX input on the MAC, perhaps therein lies the problem. Maybe you are overloading the inputs with the output from the GCPH. Does the sonic degradation stay the same if you turn the level control of the GCPH way down and use the MAC for volume adjustment? |
66 dB? Why do you need so much gain for a MM cart? At 66 dB and 1:30 to 2 you are getting about 60 dB total gain which is x1000. For a nominal 4 mV (at 1K Hz) MM cart output, that is 4 volts output!
That's a lot for a line amp input. |
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. |
Michel:
48-54 dB sound more reasonable. Remember that gain is only as registered on the gain setting when the volume control is full CW. If used at 1:30 - 2:00, its about 6 dB lower.
My comment about the input capacitance value of 100 pF comes from a direct inquiry with PS Audio. I did not confirm the actual value myself. Even if you open the unit, you cannot read the component values because they are all surface mount chip components. You need a magnifiying lupe just to see them! |
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. |
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. |
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. |
Michel:
With all fairness to PS Audio, how can you blame them when the product sounds much better directly connected to the power amp? Adding any amp in between is most likely to reduce the quality of the sound, but that is not the fault of the GCPH.
As for the comparison with the AQVOX, perhaps the GCPH is inferior to that product, I don't know. I took a look at the 6moons review of this product, and it looks quite interesting. But remember Stereophile also gave the GCPH a rave review as well. So you cannot tell much about the sonic -preferences of a product from reviews. Sometimes when you make comparisons you get surprised, but you can only chalk that up to learning. The AQVOX appears to be more expensive (1000 euros list which is $1200-1300 US) and you can typically get a new/demo GCPH for $750 (as I got mine from Parts Express). But cost is another parameter that may not be all that relavent. Some folks like the CA products (if modified) and they are considerably cheaper than the GCPH. If you like the AVQOX that much, then sell the GCPH and move on. Life is too short to fret over how the GCPH should sound versus how it actually sounds.
You have nothing to lose by having PS Audio check it out. I cannot imagine anything about the circuitry in the GCPH that would degrade the sound through pre-amps that would not also be heard through a power amp. Unless you have the gain of the GCPH too high and you are overloading the pre-amp which would degrade the sound. But again, that is not the fault of the GCPH but how you are using it. I think I suggested you run your tests with the gain on the GCPH as low as possible if you are feeding a pre-amp. |
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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