Loading and Frequency Response

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dave slagle
Posts: 2102
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC

Loading and Frequency Response

Post by dave slagle »

I was asked about how the load seen by the cartridge effects the frequency response so I made some quick crude measurements of a shelter 501 and a denon 103R. The test record was the CBS STR-120. The sound card was a Focusrite Scarlett 2i2. captures were made with audiotester. The tonearm cable fed the input of a 1:20 SUT to get 26dB of additional gain above the ~56dB gain of the sound card to increase the S/N ratio. The 2i2 has a published input Z of 1.5MΩ which loads the cartridge with 3,750Ω in the "U" plots. A 13Ω resistor was then placed directly across the cartridge for the 13r set of plots.

No levels were adjusted and not much care was taken in cartridge setup since I have yet to see setup materially effect this particular measurement.

here is the shelter 501 which is a 12Ω cartridge under the two loading conditions. I generally assume there is an additional 2Ω of source impedance for the tonearm cabling and the 5dB change in amplitude is in line with what I would expect for a 14Ω source feeding 3750Ω and 13Ω. The left channel is about 1dB hotter than the right but the overall shape of the plots do not reveal any appreciable changes in frequency behavior between the lightly and heavily loaded case. I am reasonably confident that If I ran the same setup 10 times you would see a similar amount of measurment variation from what should be identical plots.

shelter 501.png
shelter 501.png (56.32 KiB) Viewed 8801 times

and here is the 103R which is 15Ω. In this case it is the Right channel that has more output and it is of interest that the loaded case reduces the output by 7.5dB in the right channel and 9.5dB in the left channel which clearly shows the load is below the internal impedance of the cartridge. At this time I do not have a good answer for the 2dB increase in difference for the loaded case.

denon 103R.png
denon 103R.png (56.27 KiB) Viewed 8801 times

In order to address some of the squirrels in the unsmoothed plots here are the individual channels for both cartridges showing that there is a fair amount of system / record induced artifacts that are consistent from cartridge to cartridge. It is interesting to note that the Left channel has a 9kHz 'blip' and the Right channel a 10kHz one.

R channel.png
R channel.png (56.45 KiB) Viewed 8801 times
L channel.png
L channel.png (56.43 KiB) Viewed 8801 times
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