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.
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.
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!
Yep - that rubber on the underside of the lid looks similar; maybe I should get it going.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.
Yep - that rubber on the underside of the lid looks similar; maybe I should get it going.
Thanks for the tip.I can recommend adhesive neoprene rubber sheet to replace the foam. Easily available on Ebay in a variety of thicknesses:
http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=261355714768
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
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. 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.