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Home » Audio » Measurement » Turntable Cartridge Measurements
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| Re: Turntable Cartridge Measurements [message #89540 is a reply to message #89424] |
Thu, 10 January 2019 12:10   |
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Wayne Parham
Messages: 18783
Registered: January 2001
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Illuminati (33rd Degree) |
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On Bruce Heran's advice, I have purchased and received the "Analogue Productions Ultimate Test LP." I haven't even opened it yet, because I'm going to finish my stylus microscope evaluation first. But I am getting prepared.
I already have an oscilloscope, distortion analyzer, signal generator, frequency counter and a bunch of other test equipment like tube testers and what not. As an electrical engineer, I've aquired all kinds of test goodies, and used them for many years. I also have several acoustic test systems, like LMS and WTPro. So I'm good on test equipment.
But it does occur to me that none of this stuff can be synchronized. It's all stand-alone equipment. So while I can see the waveform and its amplitude, and can also see the frequency of a sine, I cannot log them together. The way systems like LMS and WTPro do it is they generate their test signal and then listen to it. So they can know what they sent to compare it with what they get back.
In this case, the test signal will come from a record. I'll simply be watching it with a scope and frequency counter. I'd have to record the amplitudes and frequencies manually. Maybe the sweep goes slow enough that's not difficult, I don't know. Maybe I should just open up the album and follow its directions. 
But I do anticipate that it might be useful to have a system that can log frequency and amplitude simultaneously. So I'm thinking about trying out a PC-based oscilloscope. I've never done that 'cause I have the "real thing." Never needed or thought I wanted a PC 'scope. But now, I'm thinking it might be useful for this, so I can log frequency and amplitude, and perhaps export that to something to make a frequency response chart.
Towards that aim, I'm looking at software called Daqarta. I'll let you know as I make progress.
I'm also thinking about the RIAA curve in the phono stage. I'll be measuring a system, not just the cartridge. Significant aspects of the signal path include the cartridge stylus (mass/spring), its motors (coil/magnet), the cartridge load impedance (L/C/R) and the RIAA filter function within the phono stage. So these measurements won't totally isolate the cartridge.
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| Re: Turntable Cartridge Measurements [message #90655 is a reply to message #90654] |
Mon, 08 July 2019 19:40 |
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Wayne Parham
Messages: 18783
Registered: January 2001
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Illuminati (33rd Degree) |
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The sweeps (which are actually stepped sines) are of equal amplitude so if the reactive load on the cartridge and the RIAA equalization is accurate, then the output of at all frequencies will be equal amplitude.
I switched from oscilloscope view to spectrum view for this test. That made it easier to see the signal and its amplitude: As frequency rises, the position of the signal simply moves to the right on the graph.
There are a couple things I would have liked to have done differently. One is the horizontal (frequency) scale, which is linear and goes clear out to 24kHz. That's fine when doing high-frequency sweeps, but it would have been better for me to have switched to a view that limited the range to 1kHz, placing that at the far right of the chart for low-frequency sweeps. I'm not familiar with Daqarta yet, so I don't know how to do that or if it's even possible.
The other thing I would have liked to have done was to sample the screen captures more often, so I could capture all the signals. I had a screen capture program set to grab the Daqarta window every half-second, so it missed some of the signals. I still got a good representation of the behavior of the system though. Maybe next time I'll study the program more so I can capture all the frames, perhaps as an animated GIF.
Stepped sines from 1kHz to 10Hz:
Amplitude response looks pretty good and flat between 10Hz and 1kHz.
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