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Old 25th August 2005, 01:07 PM   #11
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Good to see an old thread reviving.

Ok, first I'll re-open my PP2 and will certainly change the load resistor to 47K. I also need to fine tune the VTA of my arm for the Denon cartridge.

Yes Henkel, I'll try to find your answer.
Just a question why don't you try the MC input instead of the MM one. It has much higher gain (but probably to much but worth trying)

The MM section seems to use a basic op-amp gain section. It is maybe not that difficult to figure how to increase the gain.

We will see. I just hope your not in a hurry. I may take a few weeks before I have the time to look at the matter.

I'll let you know.

Bye...
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Old 26th August 2005, 09:05 AM   #12
henkel is offline henkel  Malaysia
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Algar,

Thanks for your reply.

I did try to use the MC input of the PP-2 but the RIAA equalisation is not set up for MM. The sound is louder at 52 db gain, but I got sound that's rolled off from high mids onwards.

Kinda hard to describe but is a very mono like sound but in stereo!

I still need the MM gain section to be higher.

Your help is much appreciated.
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Old 29th August 2005, 01:13 AM   #13
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Henkel I got your answer. The gain is set by R37 (Left Channel), and R28 (Right). The default value is 249R, gain of about 34dB

If you parallel a resistor of this value with R37 or R38 you'll have these gains:

R38 or R37 // 220R = Gain 40dB
// 100R = Gain 45dB

You should use metal film 1% resistor, otherwise you can have left and right gain missmatch.
Solder the resistor on the bottom of the PCB, much easier.

Try that and let me know.
The image is showing where R37 and 38 are located.

Have fun.
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Old 29th August 2005, 01:15 AM   #14
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I did a small hand schematic of the MM stage, left channel only. I don't guaranty the accuracy
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Old 29th August 2005, 11:26 AM   #15
henkel is offline henkel  Malaysia
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Algar,

Thanks a million.

Very much appreciated what you did.

Will definitely try it out.

Once done, I'll let post the results.
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Old 29th August 2005, 01:02 PM   #16
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the predecessor, the PP-1, was reviewed by Gary Galo in Audio Electronics 3-2000. He pointed out a couple egregious errors in the design (some were pretty glaring) which have hopefully been corrected in the PP-2. One of the designers responded to the critiques, but it was pretty lame.

One thing of note in your power supply -- the capacitors across the diodes just lower the ringing frequency -- possibly bringing it down into the "hearable" region -- remember that the secondary inductance and the diode capacitance form a resonant circuit. This actually becomes important in a low level gain stage like a phono preamp -- you can demonstrate the ringing in LTSpice.

MUR860's have a capacitance of around 130pf at 24V -- try using a 390 ohm resistor in series with a 1nF capacitor --
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Old 29th August 2005, 01:56 PM   #17
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here's what I mean in EWB -- the 220nF parallel cap puts the ringing frequency around 70kHz -- "inaudible" you might say, but problematic for the voltage regulators and potentially causing unexplainable offsets on the opamps:
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Old 29th August 2005, 08:51 PM   #18
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Interesting suggestion. I may try it.

Thanks...

SB
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Old 30th August 2005, 04:07 AM   #19
henkel is offline henkel  Malaysia
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WOW!

This thread is turning into a treasure trove to NAD PP-2 users like me!

Algar, you're a genius!

I paralleled R37 and R38 resistors with your suggested resistor value of R100 and R 50, (47 actually) and got the gain that I want.

The value of R100 gave a more laid back sound as with less gain, but the R47 gave a more dynamic kind of sound and it's louder too. The beauty is that the highs becomes very airy. I settled for the R47 resistors.

I had the modded NAD benchmark against Trichord Research's Dino, a phono stage that is about 5X the price of the NAD. The Trichord was set to MM at 48db gain to match the modded NAD.

The NAD was better than the Trichord?, Nope!

As it should, the NAD did not win in any category against the Trichord, but in some respects it's actually pretty close. The most noticeable areas areTrichord had a clear upper hand when it comes to bass control and definition. The Trichord is also a lot better in letting low level resulotion thru the system.

Now I can't wait to do more on the little NAD.

Cheers! guys.
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Old 2nd September 2005, 04:38 PM   #20
henkel is offline henkel  Malaysia
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After a few days playing with the louder PP-2, I noticed that certain records that sound louder, will overload the input of the pre-amp.

So I switched back the R100 resistors in and settled for 45db gain.

jackinnj. What do you suggest I replace the 220nf caps (the brown ones next to C41 and C42 on the board) with?

Are you saying that I should replace the said caps with a 390ohm resistor in series witha 1nf capacitor?

Curious to get more out of the NAD PP-2 please help?

Thanks.
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