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Measuring phono stage RIAA accuracy with a computer
Measuring phono stage RIAA accuracy with a computer
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Old 4th April 2018, 10:00 PM   #191
scott wurcer is offline scott wurcer  United States
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Originally Posted by MarcelvdG View Post
Getting back to measuring phono stage accuracy, does anyone know a way to measure the response of the cartridge and amplifier together other than simply playing a test record and hoping it was recorded accurately?
I don't see a definitive way without including the vinyl/stylus interface. B&K used a precision accelerometer in reverse as a stimulus, but I don't remember the details.
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Old 4th April 2018, 10:29 PM   #192
Pano is offline Pano  United States
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Measuring phono stage RIAA accuracy with a computer
Didn't SY once run the test signal thru the cart? Not sure if that would make a useful difference.
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Old 4th April 2018, 10:48 PM   #193
scott wurcer is offline scott wurcer  United States
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Didn't SY once run the test signal thru the cart? Not sure if that would make a useful difference.
I've done that too but it leaves out all the mechanical effects.
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Old 4th April 2018, 11:36 PM   #194
Conrad Hoffman is offline Conrad Hoffman  United States
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Originally Posted by scott wurcer View Post
I don't see a definitive way without including the vinyl/stylus interface. B&K used a precision accelerometer in reverse as a stimulus, but I don't remember the details.
Never got around to trying it, but I'd think any small piezoelectric disc would be a good exciter for a cartridge, especially if you glued a small piece of a record to it, so the stylus was in a groove. A small disk can have a self resonant frequency in the hundreds of kHz or higher.
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Old 5th April 2018, 02:15 PM   #195
scott wurcer is offline scott wurcer  United States
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Originally Posted by Conrad Hoffman View Post
Never got around to trying it, but I'd think any small piezoelectric disc would be a good exciter for a cartridge
When I tried them the response was not too flat. There are precision piezo-positioners (some <$40) with self resonances as high as 250k. Piezoelectric Actuators - Thorlabs

Looking over the specs they might be impossible to use at 20kHz since the capacitances are huge. The app notes might ave some good ideas for linearizing cheap disks.
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Old 6th April 2018, 05:59 PM   #196
stocktrader200 is offline stocktrader200  Canada
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MarcelvdG, I am going to try a cheap in ear headphone speaker glued to a piece of aluminum then place the needle on it with the turntable unplugged. measure the results driving the speaker from an iphone signal generator.
I will see if it requires an RIAA eq. network between the iphone and 32 ohm speaker.
if the cone holds .5 to 1.5 grams it should work
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Old 7th April 2018, 10:38 AM   #197
davidsrsb is offline davidsrsb  Malaysia
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Originally Posted by scott wurcer View Post
...Looking over the specs they might be impossible to use at 20kHz since the capacitances are huge...
Looking at the smallest 2AB part with 9nF, ie Z=884, this shouldn't be too hard.

The displacement has hysteresis, which means there are some large distortions to be accounted for
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