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NAC 12 restoration project

Hi,
nothing wrong with the Alps Blue. The original pot just sound a lot better. Swap the pot and you take away much of the surprisingly good performance of the Nac12 imo. I had 3 examples of the Nac12 here and have tried both the Alps Blue and Tocos variant in all of them.
 
I continue my experiments with one of the NAC 12. After the new tants burn in period ended, I replaced the supply decoupling caps on the 321 and 324 boards.



In contrast to the first upgrade, at first I did not like the sound at all. The bass was great, details increased, but at the same time I felt a lack of intonation and nuances and a lack of involvement in general. There were also problems with rhythm. I listened to the preamp for two or three days, after which I was ready to return back to the old caps. I used the second NAC 12 and the NAC 42 for comparison. And the result was not in favor of the upgraded preamp.

But first, I decided to leave preamp for a week permanently connected to my Hi-Cap. During this period I brought him back in and listened to it a couple of times, without a positive result. But now, after 2 weeks, the sound suddenly came back to “normal”. I expect some changes in the next few days, but today it already seems to me that this is a step in the right direction.

After some time, I plan to continue experimenting with the caps , this time they will be feedback caps on 321 boards.

Thought I'd resurrect this thread, as my Nac12 (serial no. 0722) is going through exactly the same process. Like yourself I'd replaced all the tant caps (necessary as a couple had gone bad) - the Nac12 sounded simply stunning at this point, with all the original ROE caps in place, and they must be close to 40 years old in my unit! I then replaced just the psu decoupling caps on each card with 47uF Nichicon KZs, and the sound is just not great compared to how it was before.

It's been 4 days now, but it just sounds a little lifeless, not exactly dull, but not a patch on how it sounded before. The sound before was incredibly lifelike & vivid, to the extent other people in the house (who aren't usually interested in HiFi) were all amazed recorded music could sound so good. It pulled off that trick of making your speakers sound far larger than before, just enveloping you in the music. Amazing bass response that really could kick, sparkling sound full of life. A real sense of weight to instruments. Valve-like midrange, superb on vocals and tonal 'colour' & warmth. Now it just sounds kind of average. Flat. Surprising as I've always had good results with Nichicon KZs in the past, albeit as signal couplers only.

VERY very tempted to switch back to the old ROE EKs now, but I'll give it another few days I guess. I've experienced the frustration of the burn-in effect of caps before, but didn't think it would be such a marked effect with psu decoupling caps!
 
Thought I'd resurrect this thread, as my Nac12 (serial no. 0722) is going through exactly the same process. Like yourself I'd replaced all the tant caps (necessary as a couple had gone bad) - the Nac12 sounded simply stunning at this point, with all the original ROE caps in place, and they must be close to 40 years old in my unit! I then replaced just the psu decoupling caps on each card with 47uF Nichicon KZs, and the sound is just not great compared to how it was before.

Agreed in your finding and descriptions. I have tried some of the acoustica.org mods. Also caps from Samwha and Nichicon KZ. I think Nichicon KZ is the best of that lot. But with some ROE capacitors rated at 25v/47 bought from Poland via Ebay thing fall into place again, the Naim sound was back. I have some Naim cards in the house and have swapped around a bit. A pair of 324/7 buffer boards with new Kemet tantals and the untouched original 321/2 with green tantals you can see on the pic gives the sound here. The green tantals is of the brand 'ero-tantal'. My Nac12 has sn 1067 - I wonder which year it's produced.
Right now I use the Nac12 with NJ-cards and it sounds great too.

IMG_3036.jpg
 
Agreed in your finding and descriptions. I have tried some of the acoustica.org mods. Also caps from Samwha and Nichicon KZ. I think Nichicon KZ is the best of that lot. But with some ROE capacitors rated at 25v/47 bought from Poland via Ebay thing fall into place again, the Naim sound was back. I have some Naim cards in the house and have swapped around a bit. A pair of 324/7 buffer boards with new Kemet tantals and the untouched original 321/2 with green tantals you can see on the pic gives the sound here. The green tantals is of the brand 'ero-tantal'. My Nac12 has sn 1067 - I wonder which year it's produced.

I'm always glad when my findings tally with somebody elses - and it's not just my imagination :cool:

I bought some NOS 47/25V from the same source, but also got some 47/40V from a German seller on Ebay last week. So I have plenty of spares.

Today is the fifth day with the Nichicon KZs in the decoupling positions only, and I've been playing a lot of music over those five days, and not really enjoying it so much. But my opinion was still unchanged, so I carefully desoldered them, and re-installed the original ROEs which I'd kept. The sound I love is back again. They just sound more open & natural, and that bass is truly cavernous! Subjectively it seems that somehow the ROE caps respond 'faster' to the signal than the KZs - my overriding impression is somebody has let off the handbrake! Perhaps I just prefer the sound of old worn out caps?! ;) Anyway, I'll keep them in there now and periodically check them for any signs of leakage etc.

DSC_0441.jpg
 
Well, I saw this thread and it reminded me I've got a 12S which lives in the bottom of a wardrobe, so I went and got it and took some photos...

GTnrY6K.jpg

EWCXuZZ.jpg

3v95hut.jpg


As far as I know it is all original and I think the foam/rubber padding inside decayed; as far as I can recall, I've never powered it on!
 
Well, I saw this thread and it reminded me I've got a 12S which lives in the bottom of a wardrobe, so I went and got it and took some photos...
As far as I know it is all original and I think the foam/rubber padding inside decayed; as far as I can recall, I've never powered it on!

This is what the example i use today looked like when it arrived last year, apart from the phonocards i swapped from 322/1 to 322/4, when i powered it up to test before I took it apart for cleaning.
Take a look and see if the cards are where they should and test the preamp.

12s3.jpg
 
This is what the example i use today looked like when it arrived last year, apart from the phonocards i swapped from 322/1 to 322/4, when i powered it up to test before I took it apart for cleaning.
Take a look and see if the cards are where they should and test the preamp.

12s3.jpg
Yep - that rubber on the underside of the lid looks similar; maybe I should get it going.
 
Yep - that rubber on the underside of the lid looks similar; maybe I should get it going.

Give it a try - it's often been said that Naim used to test the Nac52 aginst a Nac12 as a quality check at the factory, so it was held in high regard by Naim themselves. I'm delighted with mine, and all it needed in the end were new DIN sockets and tantalum caps.

Would be interested in what you think of yours.
 
Actually, I had one years ago with a 140 and I replaced it with a 62S; in all honesty the 62S was nowhere near as good.

I might get it going and compare with my 82.
 
Quick & easy 'mod' for the Nac12 (and probably other Nacs too) is to take out the relay board, and then add bypass wires to the pins. You connect pins 3 to 4 and 2 to 5. The result is a cleaner signal path. Those relays are also getting on now, and who knows what condition they're in inside. I asked Naim about replacement relays but they weren't helpful, so this seems like a better alternative.

I could also hear no difference in turn on 'pop' loudness with or without the relay board, so I see little point in using one, though of course your situation might be different depending on equipment used. Best to test first with an old pair of speakers connected.

I noticed an immediate increase in clarity & solidity. I think I'll solder the bypass wires into place now, I can't see the point in going back to the relay board now.
 
Looking at the insides of the 12, i just love it's simplicity when compared to the newer naim pre's. Even compared to the 72 i own it looks a lot less messy.

Stu
 
Hi John,

Thanks for the reminder to try removing the relay. I have done it and agree with your results. I soldered two signal wires straight fom my 821A boards directly to the din socket. A few connections removed from the signal path.

I am happy with the results.. Once i get my voyagers up and running with velleman speaker protection there won't be any thump at all.

Stu
 
Hi John,

Thanks for the reminder to try removing the relay. I have done it and agree with your results. I soldered two signal wires straight fom my 821A boards directly to the din socket. A few connections removed from the signal path.

I am happy with the results.. Once i get my voyagers up and running with velleman speaker protection there won't be any thump at all.

Stu

I'm glad you had sucess with this easy mod too Stu. I suspect the contacts inside my relay were probably starting to corrode (even though it's supposedly sealed) as I got a definite increase in clarity after bypassing it. I think it really holds back the performance otherwise. I must get around to soldering directly to the DIN socket too to bypass the unnecessary connections.

Amazing pre-amp :)
 
Hi John,

I had not considered contacts degrading in relays. If that happens then it may be a good idea to replace the ouutput relay in my CD3.5.

Stu
 
The muting relay is not in circuit when playing - it shorts the output when muted. Contact degradation would mean the turn on thump comes through.

If you can't here a turn-on transient, relay is OK.
 
The muting relay is not in circuit when playing - it shorts the output when muted. Contact degradation would mean the turn on thump comes through.

If you can't here a turn-on transient, relay is OK.

Is there a diagram of how this circuit works? I'm obviously not understanding how it works at the moment. If the output is shorted to mute it, surely taking the board out of the unit would then be enough? But as it stands one needs to link pins 2 to 5 and 3 to 4 to get audio out when not using the relay board. This suggests the same linking of those pins is done within the relay when on to pass audio. What have I missed?

The output pop was still quite loud with the relay in place on my unit, so I think mine was on its last legs anyway.

At any rate, I'm going to bypass that whole relay section and wire direct from the card pin output points on the underside of the pcb directly to the din output, using the same orange & purple wiring, so it sort of looks official ;)
 
Is there a diagram of how this circuit works? I'm obviously not understanding how it works at the moment. If the output is shorted to mute it, surely taking the board out of the unit would then be enough? But as it stands one needs to link pins 2 to 5 and 3 to 4 to get audio out when not using the relay board. The suggests the same linking of those pins is done within the relay when on. What have I missed?

The output pop was still quite loud with the relay in place on my unit, so I think mine was on its last legs anyway.

At any rate, I'm going to bypass that whole relay section and wire direct from the card pin output points on the underside of the pcb directly to the din output, using the same orange & purple wiring, so it sort of looks official ;)

This relay board talking reminded me that I had some new Philips 47uf/63v caps here from an earlier Nac12 adventure. I swapped it yesterday and after a minute or so of charging it was up and go again. The loud pop is now gone. And I am sure my Nac12 sounds better and smoother aswell.

ph_zpss7tvwkag.jpg
 
This relay board talking reminded me that I had some new Philips 47uf/63v caps here from an earlier Nac12 adventure. I swapped it yesterday and after a minute or so of charging it was up and go again. The loud pop is now gone. And I am sure my Nac12 sounds better and smoother aswell.

Try bypassing the relay completely ;)
 


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