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Turntable Cartridge Measurements [message #89424] Fri, 21 December 2018 15:52 Go to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17357
Registered: January 2001
Illuminati (33rd Degree)

In the "Stylus Inspection" thread, we got sidetracked onto the related topic of cartridge evaluation. So that prompted me to start a new thread, specifically about the ways to measure cartridges.

I found an article in the attached "Bruel & Kjaer Technical Review" journal from 1976. Pages 25-34 discuss using an accelerometer to provide a signal for testing turntable cartridges.
I understand that some people use a test record instead of an accelerometer to vibrate the stylus. That would be good too and probably more accessible for most people.

I've tended to trust cartridge manufacturers to provide products that perform well, having flat frequency response and low distortion. They are sort of a "trusted reference" for me. But it occurred to me that this is quite an assumption.

Even if the cartridge provides flat response with the stylus provided when it is connected to the right load impedance on the input of a phono stage with the perfect RIAA curve - How much am I deviating from that years later when I switch to an aftermarket replacement stylus? And how much of an impact does the load resistance and capacitance matter? The RIAA curve in the phono stage isn't a cartridge issue, but it definitely matters too, and its filter function may depend upon and interact with the cartridge source impedance. So these are the things I'd love to see actually measured.
Re: Turntable Cartridge Measurements [message #89540 is a reply to message #89424] Thu, 10 January 2019 12:10 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 17357
Registered: January 2001
Illuminati (33rd Degree)

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. Laughing

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 an open source system creatively named the Visual Analyzer. 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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