NAD PP2 Phono Preamp Upgrade - diyAudio
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Old 26th December 2004, 10:30 PM   #1
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Default NAD PP2 Phono Preamp Upgrade

I just bought for a song an almost brand new NAD PP-2 Phono Preamp. I bought it to use before I finish my Ono preamp.
I can also compare the sound and see if my Ono is as good as the review are saying it is

This is the inside. Pretty neat for such an inexpensive preamp. Already, for the price, it seems to be a bargain.

Very well built, metal film resistors, low noise transistors. Good quality, gold plated connectors, good, small casing. MM and MC separate inputs. Good specs. Difficult to beat even by diy.

If it is worth it, I plan to replace the cheap electrolytic caps inside with some Panasonic FC that I have in stock, can't hurt I guest.
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Old 26th December 2004, 11:22 PM   #2
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One thing that can probably be upgraded is the cheap 24V, 100ma wall adapter external power supply. I did some measurements inside the unit. It is using a LM317, adjusted at 20V. The input of the regulator is 26.6Vdc but has 167mv ac of ripple.
The output is 20.1V at 2.4mvac of ripple. I agree to some other posts on the net, that the circuit cannot sink more than 100ma, so there is probably no reason to have a supply more powerful. But a more silent supply can probably lower the noise floor of the preamp.

Anyway, I had all the necessary parts in stock (from previous projects) to build an 24V upgrade power supply. It took a few hours and there it is.

It is using an EMI filter, soft recovery diodes bridges with Wima snubber caps and a nice Panasonic FC 3300uf, bypassed with an 3.3 uf ERO cap. The cheap plastic power cable is now replaced with a nice length of Canare L-2T2S, twisted copper pair, 95% shielded with copper braid. The AC socket can now accept better power cord.

This little supply provides at the input of the preamp 23.8Vdc, 62mvac of ripple and now the output of the regulator is much quietter at 20.1Vdc and less than 0.5mv ac of ripple!

As I said, the parts are probably not optimal, the transfo can be bigger, can have more filtering caps, etc, but they were in stock, and I can do a quick check and see if I get improvements.
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Old 26th December 2004, 11:26 PM   #3
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I had a nice aluminium little casing. Here a side view of the EMI filter with built-in AC socket, fuse and power-on switch. There was two holes there. I put a led for power-on and a GND screw.
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Old 26th December 2004, 11:27 PM   #4
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Here the PP2 preamp with the new supply. And soon, some listening comments on this little preamp.
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Old 27th December 2004, 12:40 AM   #5
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and here the little schematic. As I said, no listening parts selection session, just as built using good desing practice.
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Old 27th December 2004, 06:03 AM   #6
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This little pre will certainly help vinyl sound worse than cd.
The last good phono NAD made was the phono section of a 3150 integrated (early eighties?).
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Old 27th December 2004, 08:01 PM   #7
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I don't agree. I'm listening to it right now and the sound is very pleasant. A little bit on the lean side but medium and high are soft and musical. The bass are a little lean but it may be my cartridge, a MC Denon DL-110, see http://www.needledoctor.com/s.nl/sc....it.A/id.234/.f
http://www.positive-feedback.com/Issue15/denondl110.htm

The DL-110 output impedance is 160 ohms. The PP-2 MC input impedance was 100 ohms. Searching on the net, I found that the input impedance for MC should be about 2.5 times the cartridge coil impedance, see: http://www.xs4all.nl/~rabruil/ttadjust.html

So the cartridge was 160R X 2.5 = 400R. I had RN55 film resistors 499R in stock. I opened the preamp, found that the two input impedance matching resistors were R05 and R06, 100 ohms resistors indeed. I installed the 499R resistors instead inside the PP2 and Voilą!

The bass is much better. The sound from this little preamp is very acceptable and goes quite well for casual listening.
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Old 21st January 2005, 01:29 PM   #8
Werner is offline Werner  Europe
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Quote:
Originally posted by Algar_emi
Searching on the net, I found that the input impedance for MC should be about 2.5 times the cartridge coil impedance,
That is just an unfounded opinion. The true required load will depend on the actual case.

Anyway, a high-output MC like the DL-110 is designed for a load impedance of 47k. Not 100, not 500.

Would you care to reverse engineer the PP2 and post a schematic here? I may embark on a modification programme for an acquiantance, but would like to know if it is worth the trouble. I don't have a PP2 on hands.

Thanks
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Old 21st January 2005, 01:41 PM   #9
SY is offline SY  United States
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Algar, do you have any connection between power and chassis/earth ground in the PS box?
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Old 24th August 2005, 06:59 AM   #10
henkel is offline henkel  Malaysia
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Hi! Algar,

I am a newbie to this DIY thing, most of my DIYing is done on soldering cables to RCAs and power sockets.

I am also new to this phonostage thing, but I do have an NAD PP-2 which I had upgraded the power supply, not as impressive looking as yours, but still got some improvements out of it.

I am now having a slight problem which I really hope you can help me.

I am using a Rega Ellyias MM Cartridge on my table to go with the NAD PP-2, but found the MM gain not insufficient. The NAD specs 34.5db gain for MM. I need something between 42-45db gain.

I was informed by a local DIYer, that by piggybacking a pair of resistor at the pre-out area of the NAD can achieved the desired results. However, he is unable to help me more as distance separates and photos via e-mail can only do so much.

Since you have the NAD with you and have seen the phono board,
can you help me identify which resistors to piggyback and if possible value of resistor required?

Your help is much appreciated.

Thanks.
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