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Inductor in phono stage input
Inductor in phono stage input
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Old 19th July 2019, 03:31 PM   #11
billshurv is offline billshurv  United Kingdom
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Inductor in phono stage input
Which cartridge manufacturer are you thinking of in this case?
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Old 20th July 2019, 09:41 AM   #12
DF96 is offline DF96  England
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Ortofon?
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Old 20th July 2019, 09:43 PM   #13
billshurv is offline billshurv  United Kingdom
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Inductor in phono stage input
Glad you said ortofon as Hans measured one of those. Attached is his raw measurement, equivalent model and some loading examples. This is JUST the coil being measured and an end to end measurement still needs to be done. Now for this model (super OM) Ortofon give a bit of a barn door to aim at with 200pF-500pF recommended. Loading at 47k||150pF in the simulation as you can see gives an electrical roll off of 2dB at 15kHz so you can see that a higher capacitive load would be a way to reduce that. In fact a different resistive load does a far better job as can be seen.



This is by no means proof as there are missing measurements, but it's a pointer that this oft repeated statement about MMs having a mechanical roll-off might not actually be the case. Hopefully before too long we can get the missing measurements and make some progress.
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Old 22nd July 2019, 09:56 AM   #14
DF96 is offline DF96  England
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OK. It is possible that I am just repeating a popular myth, but I'm sure I saw some evidence somewhere some years ago.
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Old 22nd July 2019, 10:13 AM   #15
billshurv is offline billshurv  United Kingdom
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Inductor in phono stage input
I've not seen measurements that isolate the different aspects, but would love to find some. There are some compelling analyses, for example the attached from a paper Steven Van Raalte did for linear audio (diagram attached with permission from Jan who is a good egg )


This shows the electrical roll off from the generator as 'E', the assumed mechanical resonance as 'M' and the combined output as 'S'. This fits some measurements I have seen so it would be easy to say case closed. Luckily there are still a few inquisitive types like Hans and George who will do measurements never published before.



All good harmless fun
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