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Help Me Understand Input/Output Voltage Specs
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Graham Slee View Drop Down
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Points: 16298 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 1:08am
There is noise due to thermal agitation in any conductor including semiconductors and resistors, but with increasing resistance noise increases, so for example the noise of a 1k resistor is approx. 4nV per sqrt Hz, but will be lower if resistance is lower and higher if resistance is higher.

A magnetic cartridge winding is inductive as well as resistive so its impedance rises with frequency, and impedance is ac resistance, and so requires complex calculation such as a spreadsheet, but I cannot vouch for this being accurate.

We also need to know 'at what frequency' and the amplifier's equivalent input noise EIN at that frequency.

-68dB is measured at the output so we need to add gain, which is 42dB approx. at 1kHz for the M, making EIN -110dB at 1kHz.

So if input noise (noise into the input) is -74.8dB at 1kHz it is 35.2dB worse, and so noise due to the cartridge makes the output noise -32.8dB (68dB - 35.2dB).

But what is the cartridge noise really at 1kHz?
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Points: 1525 		Post Options Post Options   Thanks (0) Thanks(0)   Quote patientot Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 2:29pm
It looks like the author of the site split things up into 10 frequency bands then used some formulas to arrive at a calculation for the whole. They don't give a number for 1kHz exactly in their spreadsheet, but here is a portion of what it looks like. 
SL-1200 MK7 (modified) + Reflex M + PSU-1 used with AT150-40ML, AT VM95ML, Stanton 680mkII + Ogura, and Shure M35X cartridges.
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Points: 16298 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 2:44pm
Sorry, I'm lost.

Best I can do is wire a spare cartridge across a phono stage input and measure the noise on my AP, which will give you a true wideband noise indication.

Unfortunately that must wait until other jobs are done and I'm working on the analyser again.
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