Pickup Stylus Mechanically Exciting - diyAudio
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Old 5th August 2008, 10:11 AM   #1
oshifis is offline oshifis  Hungary
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Default Pickup Stylus Mechanically Exciting

Is there any way to mechanically exciting the stylus in horizontal and/or vertical direction? I mean using some kind of transducer instead of playing an LP. The purpose would be to use a variable audio signal generator, find the resonance frequency and Q factor, then optimize the damping to get maximally flat response around the lower cutoff frequency. Would a piezo transducer do the job? I do not want to go beyond 100 Hz or so.
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Old 5th August 2008, 10:44 AM   #2
h_a is offline h_a  Europe
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I'm not sure I fully understand.

The interesting system is the pickup+tonearm combination as this sets the resonance frequency of the whole system. As the compliance of the pickup is generally known you just need to find the effective mass of your tonearm to calculate it. In general highly compliant systems go with light arms and necessarily perform poor with heavy ones - exactly as lowly compliant MCs need heavy arms.

But if I just misunderstood you, please correct me!

All the best, Hannes
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Old 5th August 2008, 11:30 AM   #3
sreten is online now sreten  United Kingdom
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Hi,

A test record with subsonic (< 20Hz) tones / warble tones does the job.
A rig is possible but far too complicated for such a simple job, use the above.

/sreten.
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Old 5th August 2008, 12:13 PM   #4
oshifis is offline oshifis  Hungary
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Hannes,

I want to check the transfer function of the arm/pickup combination. A test record with subsonic tracks is possible, actually I am using the HiFi News & Record Review test record for this purpose. But the problem is that it contains a sweep and the exact frequency and amplitude is difficult to determine. I want to measure the resonance peak amplitude related to the passband amplitude. Just like the low-frequency rolloff of a loudspeaker, where critical damping Q=0.7 results in the maximally flat response and Q=0.5 gives minimum group delay. I think this parameter (damping factor of the arm/pickup mechanical vibrating system) is ignored at turntables.
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Old 5th August 2008, 12:24 PM   #5
sreten is online now sreten  United Kingdom
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Hi,

Convert the frequency sweep into a digital file.

Using "sample" editors it should be very easy
to ascertain the information you are looking for.

FWIW the parameter is not ignored in turntables.
Cartridges have a highish Q for very good reasons.

/sreten.
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Old 5th August 2008, 02:02 PM   #6
h_a is offline h_a  Europe
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Quote:
I think this parameter (damping factor of the arm/pickup mechanical vibrating system) is ignored at turntables.
No it is not

You just have to choose the correct cartridge for your tonearm - remember high compliant carts (typically MMs) for low-mass arms and low compliant carts (typically MCs) for high-mass arms. Then you got a mechanically perfect match, see for a calculator here ("Cartridge Resonance Evaluator")

http://www.cartridgedb.com/

But don't forget that MMs need also to be correctly capacitively loaded, otherwise you will never get a flat frequency response.

All the best, Hannes
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Old 5th August 2008, 02:36 PM   #7
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I think you can do this, but it's not very easy if you don't have access to some pzt materials. I'd use a small disk made of "soft" piezoelectric ceramic to get maximum motion from the drive signal. Remember that these are almost purely capacitive, so the signal generator will have to be ok with such a load. Pretty sure you will also have to equalize it. Mount the disc on something more massive, say a 1/8" piece of brass, then set the stylus on the surface. It should be possible to tune through the resonance and measure the response. You might be able to do the same thing with a small tweeter- I've seen some that are very flat, less than 1/2". Just because they don't radiate at low frequencies doesn't mean the diaphragm isn't moving! I use a test record with a continuous sweep at a known rate- record the response and you can pin the frequency by time.
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Old 5th August 2008, 02:37 PM   #8
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by h_a


No it is not

You just have to choose the correct cartridge for your tonearm - remember high compliant carts (typically MMs) for low-mass arms and low compliant carts (typically MCs) for high-mass arms. Then you got a mechanically perfect match, see for a calculator here ("Cartridge Resonance Evaluator")

http://www.cartridgedb.com/



All the best, Hannes
Hi, he is not talking about getting the right frequency at all, /sreten.
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