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NAD pp2

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NAD pp2

Postby Wernerb » 17 Jan 2018 19:07

Does anybody know what are the numbers of the resistors in the MM part of my NAD pp 2, which make the load impedance on 47kOhm? I would like to lower the total impedance to 33 kOhm in order to adapt it to my Ortofon 2 m blue cartridge.
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Re: NAD pp2

Postby 1200y3 » 19 Jan 2018 03:57

You don't have to touch the internal components. All you have to do is place a resistor in parallel with the phono plug, to equal the load you need. Unfortunateley I can't remember how to make the calculation, and my Parallel Resistance slide rule calculator is gone, so if you can't find info on the net about "deciphering" parallel resistors, use an ohm meter and a 47k reference resistor, and select a resistor that equals the load you need.

I will try to find a classic Parallel R/C app.
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Re: NAD pp2

Postby lini » 19 Jan 2018 10:24

1200y3: Uhm, what do you need an app for? You just need to remember the formula for parallel resistance, which is 1/R(total) = 1/R(1) + 1/R(2) (+ 1R(3) et cetera...), and apply it accordingly. So you get 1 / (1/33 kOhm - 1/47 kOhm) = ca. 111 kOhm. Closest usual, easily available value should be 110 kOhm.

Disadvantage of the usual, external approach via Y-splitters and loading plugs would be an at least slight increase in cabling capacity, though. However, if one would like to avoid that, and provided there's sufficient space inside the plug shells, one can just as well integrate the resistors in the output cable plugs of the turntable.


Werner: Sorry, there used to be a schematic from some DIY-oriented audio forum one could easily find via Google's picture search, but that seems to have disappeared in the meantime. If you could provide a reasonably highly resolved pic of both sides of the PCB, it shouldn't be all to difficult to identify the responsible resistors, though - provided you'd really prefer an internal modification. Alternatively you could try to contact fellow VE user Werner (from Belgium), 'cause iirc he had provided that schematic. So maybe he can repost it here or at least send it to you...


Greetings from Munich!

Manfred / lini
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Re: NAD pp2

Postby james73_2008 » 20 Jan 2018 01:16

lini wrote:1200y3: Uhm, what do you need an app for? You just need to remember the formula for parallel resistance, which is 1/R(total) = 1/R(1) + 1/R(2) (+ 1R(3) et cetera...), and apply it accordingly. So you get 1 / (1/33 kOhm - 1/47 kOhm) = ca. 111 kOhm. Closest usual, easily available value should be 110 kOhm.

Disadvantage of the usual, external approach via Y-splitters and loading plugs would be an at least slight increase in cabling capacity, though. However, if one would like to avoid that, and provided there's sufficient space inside the plug shells, one can just as well integrate the resistors in the output cable plugs of the turntable.

Greetings from Munich!

Manfred / lini

Would that apply to these? They can be plugged straight into the input of the phono pre-amp.

Image



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Re: NAD pp2

Postby 1200y3 » 20 Jan 2018 03:39

Oh yeah right, "1 over". #-o But since I rigged up so many crossovers and filters, I found the old R/C slide card calculator along with trial and experiment to be part of the fun.
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Re: NAD pp2

Postby lini » 20 Jan 2018 08:14

James: Basically that would apply to any RCA Y-splitters. In case of good ones I'd expect a pretty small capacity around 10 pF plus another roundabout 5 pF for the loading plug, but not so good ones might as well add quite a good bit more...


Oh, and seems like I forgot the / between 1 and R(3).


Greetings from Munich!

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Re: NAD pp2

Postby james73_2008 » 12 Feb 2018 00:05

After reading this webpage I tried MM cartridge loading via the connectors below.

Image

Not being good at soldering, I made up some RCA plugs like so:

40362


I used two pairs of them (the 470KΩ and then the 100KΩ) with the 2-way connectors above like so:

40361

but I couldn't hear any difference at all. :?


Did I do something wrong?



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Re: NAD pp2

Postby lini » 12 Feb 2018 01:44

James: At least I can't imagine what you could have done wrong. Did you already record the results to your computer for easier, delay-less comparison?

Greetings from Munich!

Manfred / lini

P.S.: And just for the record, I love the funky design of Davey's loading box.
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Re: NAD pp2

Postby james73_2008 » 12 Feb 2018 01:49

lini: No I didn't, but I was doing the listening through my headphones, so I know I would've heard a difference had there been any.

Maybe I'll try again and this time record the same song with 3 or 4 different settings to my PC and see what happens!



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Re: NAD pp2

Postby jcmusic » 12 Feb 2018 17:17

Any more info on this I too want to try changing the loading on my setup. The cartridge I am using now Soundsmith (Sotto Voce) calls for a 1.5kohm load and my phono stage has the standard 47k loading. How do I get to 1.5k?
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