The issue of phono stage hiss has been widely reported on this forum. One problem is that the subjective reports seem to be very inconsistent, one persons "I don't notice it when listening" is another persons "this is unacceptable in a product like this and is ruining my enjoyment of vinyl".
At the recent Devialet event at Oxford Audio, Devialet's Mathieu Pernot made the suggestion that anyone who is suffering from the issue could take a digital recording of the phono stage and send it to him for analysis . A "needle drop rip" without the dropping the needle bit, if you like.
I had some spare time this morning, so I thought I would try this. One problem I have is that I do not have access to a Laptop PC or similar at the moment, or at least not one that I can load Audacity onto for USB digital captures. I do have a PC in the same room as the hifi, but this is a long way away from the hifi, so I ended up using a 10m USB extension cable. Not ideal, but it did work. I mention this because it is quite well known that USB cables of this length are not really suitable for audio, so this might have some bearing on my results.
As a first test, I digitally recorded one track from an LP. Playing this back, it sounded fine, so at least the overlong USB cable works, even if it is not ideal.
I then tried a 20 second recording of just the phono stage. The phono stage settings were RIAA 1976, 0.39mV, 30 ohms. Playing this back at high volume, yes, it sounds like the hiss you get from a Devialet phono stage. So far so good.
I then tried doing a "plot spectrum" frequency analysis in Audacity. The results were not quite what I was expecting:
It looks like the "hiss" content is concentrated around 30Hz. The problem is that it sounds nearer to white noise than anything at 30Hz, so this is very puzzling. Concerned that maybe the 10m USB cable was picking up something odd, I tried a capture with the USB cable disconnected from the Devialet, and got absolutely nothing, which I guess is what you would expect in the digital domain. I then remembered Mathieu's advice at Oxford, disconnect the everything from the phono stage RCA inputs. The above capture was taken with my TT still connected. I disconnected the cable from the TT completely, so absolutely nothing connected to the Devialet's phono input, and tried again, the result is below:
This is actually quite an interesting result, because it does seem to show some extra grunge that the TT is picking up being removed from the second capture. However, the plot is still concentrated around the 30Hz area, so I remain a little baffled. I suspect that I am doing something wrong in Audacity, maybe the Audacity experts out there can suggest something? I am completely new to Audacity so might well be making some newbie errors. One thing I can say is that the digital capture subjectively sounds exactly like the phono stage hiss, so this much is fine and so I can't be doing too much wrong.
Unless someone can point out the potential idiotic error I have made, I plan to send the capture to Mathieu to see what he can make of it. Meanwhile, if any other forum members could capture the phono stage hiss, it would be fascinating to compare results.
EDIT: One last thought, if anyone wants a copy of my "hiss" WAV file, I am happy to share, just send me a PM.
At the recent Devialet event at Oxford Audio, Devialet's Mathieu Pernot made the suggestion that anyone who is suffering from the issue could take a digital recording of the phono stage and send it to him for analysis . A "needle drop rip" without the dropping the needle bit, if you like.
I had some spare time this morning, so I thought I would try this. One problem I have is that I do not have access to a Laptop PC or similar at the moment, or at least not one that I can load Audacity onto for USB digital captures. I do have a PC in the same room as the hifi, but this is a long way away from the hifi, so I ended up using a 10m USB extension cable. Not ideal, but it did work. I mention this because it is quite well known that USB cables of this length are not really suitable for audio, so this might have some bearing on my results.
As a first test, I digitally recorded one track from an LP. Playing this back, it sounded fine, so at least the overlong USB cable works, even if it is not ideal.
I then tried a 20 second recording of just the phono stage. The phono stage settings were RIAA 1976, 0.39mV, 30 ohms. Playing this back at high volume, yes, it sounds like the hiss you get from a Devialet phono stage. So far so good.
I then tried doing a "plot spectrum" frequency analysis in Audacity. The results were not quite what I was expecting:
It looks like the "hiss" content is concentrated around 30Hz. The problem is that it sounds nearer to white noise than anything at 30Hz, so this is very puzzling. Concerned that maybe the 10m USB cable was picking up something odd, I tried a capture with the USB cable disconnected from the Devialet, and got absolutely nothing, which I guess is what you would expect in the digital domain. I then remembered Mathieu's advice at Oxford, disconnect the everything from the phono stage RCA inputs. The above capture was taken with my TT still connected. I disconnected the cable from the TT completely, so absolutely nothing connected to the Devialet's phono input, and tried again, the result is below:
This is actually quite an interesting result, because it does seem to show some extra grunge that the TT is picking up being removed from the second capture. However, the plot is still concentrated around the 30Hz area, so I remain a little baffled. I suspect that I am doing something wrong in Audacity, maybe the Audacity experts out there can suggest something? I am completely new to Audacity so might well be making some newbie errors. One thing I can say is that the digital capture subjectively sounds exactly like the phono stage hiss, so this much is fine and so I can't be doing too much wrong.
Unless someone can point out the potential idiotic error I have made, I plan to send the capture to Mathieu to see what he can make of it. Meanwhile, if any other forum members could capture the phono stage hiss, it would be fascinating to compare results.
EDIT: One last thought, if anyone wants a copy of my "hiss" WAV file, I am happy to share, just send me a PM.
1000 Pro - KEF Blade - iFi Zen Stream - Mutec REF10 - MC3+USB - Pro-Ject Signature 12
