If I put my notes here, I might be able to find them again later!
Phonoclone noise measurements
What we are looking at here is the Fast Fourrier Transform (FFT) of the line output from my b-board buffer recorded at 24 bit, 96 kHz by an Onkyo SE-200PCI sound card. Upstream from the b-board is the Phonoclone 3 MC phono stage, connected to a Denon DL-103. The tonearm is Denon DA-307, and the deck is a Denon DP-2000.
Four recordings, taken 1) with music playing, 2) with the tonearm raised 3) with the phonoclone powered off and 4) with the b-board and all upstream components powered off.
True 24/96 data was obtained, measurements out to 48 kHz are possible, with -130 dB noise floor. (I was using Digionsound 6 to do the recording as Audacity truncates 24 bit recordings to 16 bit in Windows due to licensing issues. The FFT was generated in Audacity however.)
The soundcard's line input may have an impressive-looking low noise floor, but it's still useless for measuring line level audio devices like the b-board because the noise of the preamp/ADC stage in the soundcard is greater than the noise of the device under test.
Clear? The broadband output noise from the b-board is not -130 dB. It's lower, you are just looking at the noise of the recording input stage of the soundcard.
The Phonoclone is much noisier, of course, because the gain is as high as 80 dB in the bass frequencies, and 60 dB over the midband. There is a little bit of hum at 60 Hz showing up, and a couple rectified power line harmonics 300-800 Hz but that is noise pickup from the cartridge/input wires rather than the phonoclone itself (trust me on that). The midband S/N is -111 dB. Input referred, that's -171 dB, or 2.8 nV sqrt/hz -- exactly the datasheet value for the OP27 opamp used in the input stage. In other words, the phonoclone noise is exactly what we expect to get from the OP27.
Playing a record, we can see lots of signal (err, music!) in the audio band up at about -40~-20 dB from 60 Hz to about 2 kHz. Signal is still present but at lower intensity in the treble, up to about 10-15 kHz. On this particular recording at least, there is no music signal present above 15 Khz, though there is some energy all the way up to 40 kHz. Most likely this is surface noise picked up by the stylus, rather than in the original recording. By recording at 96 kHz rather than 44.1 kHz it is at least possible to preserve this "natural" or analog ultrasonic signature. The stylus is producing output and we are faithfully recording it, rather than artificially truncating it at 22 khz as we would if the data was recorded at, or converted to, redbook CD sampling rates.
Finally you'll see a large peak at 10 Hz in the bass when the cartridge is running in the record groove. This is the resonance of the arm/cartridge. (This link explains it quite nicely) The 10 Hz frequency is exactly the right value, as expected when using Denon arm clearly designed with the DL-103 in mind. The intensity seems quite high, though I don't think there will be any real world issues as a consequence.
Four recordings, taken 1) with music playing, 2) with the tonearm raised 3) with the phonoclone powered off and 4) with the b-board and all upstream components powered off.
True 24/96 data was obtained, measurements out to 48 kHz are possible, with -130 dB noise floor. (I was using Digionsound 6 to do the recording as Audacity truncates 24 bit recordings to 16 bit in Windows due to licensing issues. The FFT was generated in Audacity however.)
The soundcard's line input may have an impressive-looking low noise floor, but it's still useless for measuring line level audio devices like the b-board because the noise of the preamp/ADC stage in the soundcard is greater than the noise of the device under test.
Clear? The broadband output noise from the b-board is not -130 dB. It's lower, you are just looking at the noise of the recording input stage of the soundcard.
The Phonoclone is much noisier, of course, because the gain is as high as 80 dB in the bass frequencies, and 60 dB over the midband. There is a little bit of hum at 60 Hz showing up, and a couple rectified power line harmonics 300-800 Hz but that is noise pickup from the cartridge/input wires rather than the phonoclone itself (trust me on that). The midband S/N is -111 dB. Input referred, that's -171 dB, or 2.8 nV sqrt/hz -- exactly the datasheet value for the OP27 opamp used in the input stage. In other words, the phonoclone noise is exactly what we expect to get from the OP27.
Playing a record, we can see lots of signal (err, music!) in the audio band up at about -40~-20 dB from 60 Hz to about 2 kHz. Signal is still present but at lower intensity in the treble, up to about 10-15 kHz. On this particular recording at least, there is no music signal present above 15 Khz, though there is some energy all the way up to 40 kHz. Most likely this is surface noise picked up by the stylus, rather than in the original recording. By recording at 96 kHz rather than 44.1 kHz it is at least possible to preserve this "natural" or analog ultrasonic signature. The stylus is producing output and we are faithfully recording it, rather than artificially truncating it at 22 khz as we would if the data was recorded at, or converted to, redbook CD sampling rates.
Finally you'll see a large peak at 10 Hz in the bass when the cartridge is running in the record groove. This is the resonance of the arm/cartridge. (This link explains it quite nicely) The 10 Hz frequency is exactly the right value, as expected when using Denon arm clearly designed with the DL-103 in mind. The intensity seems quite high, though I don't think there will be any real world issues as a consequence.
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