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Loading plugs Perreaux SM3 Preamp
Loading plugs Perreaux SM3 Preamp
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Old 25th March 2020, 04:54 PM   #1
freebee is offline freebee  Netherlands
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Red face Loading plugs Perreaux SM3 Preamp

I have some difficulty determining the MC cartridge loading plug values for my cartridges. The manual states that both MM (low gain) and MC (high gain) have an input impedance of 47kOhm. When I measure the resistance at the RCA terminals I get the following values: MM 460kOhm, Load 55kOhm and MC 55kOhm (not sure if this is the proper way to measure it).

When I simply plug 100Ohm in the Load terminals (to match my Denon DL-A100 MC cartridge) the volume is significantly lower than with my Denon AU-S1 SUT connected to MM (the bass is more present with the SUT).

Am I overlooking something? Are the load plugs not simply in series or is the MC impedance not 47kOhm, but 460kOhm?

Thanks for your help.

P.S. I am not very technical, so please be kind
Attached Files
File Type: pdf SM3 - 1.pdf (520.6 KB, 27 views)
File Type: pdf SM3 Phono Impedance.pdf (642.0 KB, 24 views)
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Old 25th March 2020, 05:10 PM   #2
sq225917 is offline sq225917  United Kingdom
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Its unlikey that the combined gain on the mm input and step-up combined will match the gain of the mc stage. So ignore the level discrepancy.

If you want to tilt the response to give the impression of enhanced bass try a lower value loading plug. 80 ohm should be noticeable.
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Old 25th March 2020, 06:17 PM   #3
freebee is offline freebee  Netherlands
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With the 100 Ohm load plugs give it measures 100 Ohm at the MC RCAs. Just surprised by the difference in volume and sound quality.
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Old 25th March 2020, 06:22 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by freebee View Post
Just surprised by the difference in volume and sound quality.
This is entirely to be expected.
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Old 25th March 2020, 06:24 PM   #5
freebee is offline freebee  Netherlands
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Okay. Is there something to be said for using better metal resistors in the plugs? I am using cheap ones from China now which measure within spec.
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Old 25th March 2020, 06:27 PM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by freebee View Post
Okay. Is there something to be said for using better metal resistors in the plugs?
I am using cheap ones from China now which measure within spec.
Yes, a quality name brand 1% metal film, as large in power rating as can fit in the plug, would be best.
Other resistor types have excess noise.
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Old 25th March 2020, 06:31 PM   #7
freebee is offline freebee  Netherlands
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Will try that. Thanks for your help.
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