An update to my measurements.
I have swapped a couple of emails with Mathieu, I have noticed a minor anomaly with my initial measurements, and I have also just received delivery of a copy of the "ultimate analogue test LP". So a few things to update, I shall take them one at a time.
The minor anomaly with my original measurements is that I had the phono stage set to 30 ohms. Recently, @Dev_Steve posted on my old "Cadenza Black sudden death" thread. Irrelevant here perhaps, but in my first post I mentioned how I had used RAM to settle on a cartridge loading of 140 ohms.
https://devialetchat.com/Thread-Cadenza-...dden-death
Reading back through this tread after Steve posted, it dawned on me that I have never set the phono stage as low as 30 ohms, and the gain is slightly wrong at 0.37mV. I am thinking that I must have accidently changed this is RAM whilst looking at other settings. A minor thing, and perhaps of no consequence here, but for clarity, any measurements I make from now on will be with my preferred setting of 140 ohms and a phono gain of 0.4mV.
So to the rather strange anomaly in Mathieu's analysis of my hiss recording, an "up tick" in level after 14 kHz. I mentioned in an earlier post and an email to Mathieu that this "up tick" was not picked up in my Audacity analysis. Further checking revelled that this statement was wrong. The graph that Audacity produces does not show the up tick, but the lower end of the scale is too high to show it anyway. What I have subsequently discovered is that if you hover the curser over the graph in Audacity you can manually read off the dB level, doing this reveals the up tick when I check in Audacity. So the results are consistent, it is just the case that Mathieu has better measurement kit than I do, perhaps no surprise and certainly preferable than being the other way around!
With respect to my "up tick", Mathieu offered no direct explanation as to why it is there, but he did suggest a further test. With the dual mono Pro's the master and companion amps are identical, so Mathieu suggested I could retry the measurements using the companion's phono stage. An interesting idea, as the two phono stages should in theory be identical.
Then to the test LP. The idea of the test LP is to make a "hiss" recording, then a second recording using one track on the LP which is a reference level 1 kHz sine wave. This should allow a signal to noise ratio to be established. A quick comment on the LP, it has many tracks that can be used to optimise a turntable set-up, in particular if your turntable has lots of tonearm adjustment options and similar. When I have some time to try all this, I will start another thread. For now, it is fair to say that the LP should provide me more benefit than establishing a signal to noise ratio figure, which is good news as it is not a cheap LP! What I can say is that the LP seems to be very good quality, it weighs over 200g, it is absolutely flat and true, and it gives every appearance of being a top quality pressing. It is possibly one of the highest quality records that I have, it is just a shame there is no music on it.
So what I have done now is made another "hiss recording" with my cartridge loading at a more practical 140 ohms, a reference level recording with the same settings, then repeated with the companion's phono stage. One point to note, switching to the companion phono stage was not as hard as you might think, it was a case of just swapping the SD cards between the two amps, and swapping the turntable's RCA cables also. OK, I would have needed to swap all cables if I was to permanently switch between master and companion, but it was less hassle than you might think just for this test.
Here are the results:
Hiss master
Hiss companion
1 kHz master
1 kHz companion
Interestingly, it looks to me like my master phono stage has marginally less hiss than the companion. That said, the graphs do not make total sense to me. Indeed, the 1 kHz tone graphs do not look anything like what I would expect from a 1 kHz tone. For the record, it does sound like a 1 kHz tome when you listen to it. I presume Mathieu's analysis will be better, I shall send the files to him and see what he make of it all.
Also, I am not sure how you derive a signal to noise ratio from the above data. Obviously the 1 kHz tone is louder, but what is the correct methodology to calculate a valid signal to noise ratio?
Also, both the master and companion plots still show the 14 kHz "up tick" when checked in Audacity, so this holds true for both amps and a 140 ohm loading.
I have swapped a couple of emails with Mathieu, I have noticed a minor anomaly with my initial measurements, and I have also just received delivery of a copy of the "ultimate analogue test LP". So a few things to update, I shall take them one at a time.
The minor anomaly with my original measurements is that I had the phono stage set to 30 ohms. Recently, @Dev_Steve posted on my old "Cadenza Black sudden death" thread. Irrelevant here perhaps, but in my first post I mentioned how I had used RAM to settle on a cartridge loading of 140 ohms.
https://devialetchat.com/Thread-Cadenza-...dden-death
Reading back through this tread after Steve posted, it dawned on me that I have never set the phono stage as low as 30 ohms, and the gain is slightly wrong at 0.37mV. I am thinking that I must have accidently changed this is RAM whilst looking at other settings. A minor thing, and perhaps of no consequence here, but for clarity, any measurements I make from now on will be with my preferred setting of 140 ohms and a phono gain of 0.4mV.
So to the rather strange anomaly in Mathieu's analysis of my hiss recording, an "up tick" in level after 14 kHz. I mentioned in an earlier post and an email to Mathieu that this "up tick" was not picked up in my Audacity analysis. Further checking revelled that this statement was wrong. The graph that Audacity produces does not show the up tick, but the lower end of the scale is too high to show it anyway. What I have subsequently discovered is that if you hover the curser over the graph in Audacity you can manually read off the dB level, doing this reveals the up tick when I check in Audacity. So the results are consistent, it is just the case that Mathieu has better measurement kit than I do, perhaps no surprise and certainly preferable than being the other way around!
With respect to my "up tick", Mathieu offered no direct explanation as to why it is there, but he did suggest a further test. With the dual mono Pro's the master and companion amps are identical, so Mathieu suggested I could retry the measurements using the companion's phono stage. An interesting idea, as the two phono stages should in theory be identical.
Then to the test LP. The idea of the test LP is to make a "hiss" recording, then a second recording using one track on the LP which is a reference level 1 kHz sine wave. This should allow a signal to noise ratio to be established. A quick comment on the LP, it has many tracks that can be used to optimise a turntable set-up, in particular if your turntable has lots of tonearm adjustment options and similar. When I have some time to try all this, I will start another thread. For now, it is fair to say that the LP should provide me more benefit than establishing a signal to noise ratio figure, which is good news as it is not a cheap LP! What I can say is that the LP seems to be very good quality, it weighs over 200g, it is absolutely flat and true, and it gives every appearance of being a top quality pressing. It is possibly one of the highest quality records that I have, it is just a shame there is no music on it.
So what I have done now is made another "hiss recording" with my cartridge loading at a more practical 140 ohms, a reference level recording with the same settings, then repeated with the companion's phono stage. One point to note, switching to the companion phono stage was not as hard as you might think, it was a case of just swapping the SD cards between the two amps, and swapping the turntable's RCA cables also. OK, I would have needed to swap all cables if I was to permanently switch between master and companion, but it was less hassle than you might think just for this test.
Here are the results:
Hiss master
Hiss companion
1 kHz master
1 kHz companion
Interestingly, it looks to me like my master phono stage has marginally less hiss than the companion. That said, the graphs do not make total sense to me. Indeed, the 1 kHz tone graphs do not look anything like what I would expect from a 1 kHz tone. For the record, it does sound like a 1 kHz tome when you listen to it. I presume Mathieu's analysis will be better, I shall send the files to him and see what he make of it all.
Also, I am not sure how you derive a signal to noise ratio from the above data. Obviously the 1 kHz tone is louder, but what is the correct methodology to calculate a valid signal to noise ratio?
Also, both the master and companion plots still show the 14 kHz "up tick" when checked in Audacity, so this holds true for both amps and a 140 ohm loading.
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