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Naim NAC 152XS Clone

A

alexbaxterca

pfm Member
Hi All,

Just fancy dabbling with a DIY preamp. Was thinking of modding a 72 or 102 but TBH it's £300-400 just to buy the base amp before Ive even spent anything on modding. I would prefer to start with something cheaper to get my feet wet.

I saw this blank PCB for the 152XS on ebay, less than £15 delivered.

http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=262595146327

Now it is missing the relay section for changing inputs (only has 1 input) and 1 output, and none of the gubbins driving the digital front panel. HOWEVER, this is perfect for me as I only have one digital source, and I can build some superregs to power it.

Does it look fairly legit? Ive compared to photos of the original 152XS and it seems to be. I figured for £15 plus some components it would be a nice cheap way to get the Naim sound, cut down on features I don't actually need, and build it in to a more compact case.

Anybody have any reservations?
 
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Yeah, the blank boards are very good - I have one here and it works fine. Be sure to get the components from reputable suppliers and you're all set. It's very easy to mod and upgrade the board with separate regulators, better signal path and feedback path parts etc - Acoustica has lots of tips on how to get started with upgrades. It'll be as good as a 72/102, perhaps better if you pay attention to grounding paths and how to improve on the existing ground layout...
 
Great, thanks S_J. That's exactly what I was thinking re. parts etc Will be putting in mil-spec tants in the feedback path and checking out some of the other mods on acoustica :)
 
If you only have a digital input you don't need any gain. This means you can either get rid of the gain stage altogether (if you don't need an analogue volume control), or convert the gain stage to unity gain - ths means you don't need a cap in the feedback path.
General concensus is that this cap is the most critical part for SQ - so get rid of it is my strategy.

I have one of these boards configured as a bandpass filter as part of my active crossover. The board is excellent, maybe you just need to have a look at the shared ground for the relay supply - with a bit of thought is can be bypassed.

A few years back I built some NJ cards with my own motherboard and it didn't sound as good as the 152 board, although I was using the gain stage at that time.
 
S-Man, just a question though, would changing it to unity gain get rid of the Naim sound? Just a brief summary of what I wanted to build it for..... I currently run a Chord Hugo directly in to an NCC200 power amp and use Jriver for digital volume. I have now built a Hackernap and have ordered parts for a DDDAC. Obviously I can continue to happily use digital volume here.

HOWEVER, what I wanted to play around with was maybe building a very simple Naim NAC preamp just to see whether I like having that slight colouration and Naim sound in the system rather than being a bit more purist of DAC straight to power amp. Just for fun and messing about really. Buying a used 72 or 102 and then modding it was a bit expensive for this exercise!

So I guess my question is, I probably actually want to keep the board the same but just select more choice components and add in some acoustica mods, rather than just using the board as a basis for building something else. Does making it a unity gain get rid of everything that makes it Naim, as if so I probably wouldn't bother with that approach.

Hope Im making sense!!!
 
IMO only you can/will know!!!

I asked similar questions about the PS for these circuits, whilst knowing that the only way I will really know is to try it myself:
http://www.pinkfishmedia.net/forum/showthread.php?t=191899

Sometimes I feel like I'm reinventing a full set of wheels! But I've had so many experiences of building stuff and being dissapointed that a bit of wheel reinvention is just part of the game.

So... will you lose the Naim sound???

Well IMO you don't have the Naim sound anyway, the NCC200 sounds different (I've not had or heard a HackerNAP but experience tells me it will sound different again). Applying all the Acoustica mods will change the sound. Naim would probably argue that any clone doesn't have magic Salisbury dust in it so it will not sound like a genuine Naim, and this is probably true - just using a different mains transformer changes the sound.

My interest in Naim came from hearing 2 systems using their amps that were really excellent (and I've heard many more that were not excellent). What I have discovered is that I like the results obtained by many of the engineering decisions Naim choose, but certainly not all of them. IMO (sorry I keep saying IMO, but it's important) the time aligned filter is an important part of the signal processing (SNR optimisation by bandwidth limiting) whereas the gain stage is an unneccesary complication.

I suggest you build it as standard to start with and then enjoy reinventing the wheel :)
 
The bulk of the Naim sound comes from the gain stage. Any change to it will divert from that sound. And that includes gain level, choice of feedback caps, coupling caps, etc.
 
Thanks all for sharing your experiences. Looks like Ill give it a go building stock and then, as you put it, reinvent the wheel! Like I said, mostly for fun but also for learning!
 
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