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Hello! Naim NAC 42.0 questions…

bob smog

bob smog

Member
Hello all - first post!

15 years ago, I stumbled across a Naim 42.0 preamp. I’ve never tried it out since I don’t have the matching power amp (another story) or a power supply.

Finally getting back into solid-state after a lengthy detour into tube stuff. After poking around the web, this forum seems to know a bit about Naim gear.

The label on the back reads “NAC 42X0” which I’m guessing is a reference to crossover. There is a second label over the original connection chart on the back panel and I’m thinking this might have been upgraded at some point. There is a shorting plug in the external power supply jack. It has MM phono boards as near as I can tell. Curious if this has a single rail board or a dual rail.

Anyhow, I’d love to get this up and running. I have decent DIY skills, but info on these units is a bit hard to find. I’m in Chicago and these are rare birds here.

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PFM doesn't host pics so you'll need to find an external hosting site.

That out of the way, you have one of the rarest 42s in existence, let alone North America.
IIRC there's a thin board inside in addition to the main preamp board. It's an active crossover circuit and, I think, feeds a second 4 pin output. It's probably set for Linn Kans. I've not seen one in 30 years or so. Perhaps @The_JJ has...
I'd love to see what's inside and how it's wired.
 
Thanks for the reply. I‘ve seen a pic of an XO with the thin board and this one doesn’t have it. I’m beginning to suspect that it was converted to a NAC 42.5 at some point.

I’ve contacted the admin about photos. I’ve tried flickr and google photos. I’m getting a popup that says my post is “spam-like”. Guessing it has something to do with being a new member. Will post pics as soon as things get sorted out.
 
bob smog said:
Thanks for the reply. I‘ve seen a pic of an XO with the thin board and this one doesn’t have it. I’m beginning to suspect that it was converted to a NAC 42.5 at some point.
Click to expand...
Ah, well then, if it has a link plug it's probably a 42-5 then.
 
Yep, that's a nice tidy example of a 42-5, i.e. Dual rail. The link plug simply ties them together so you can use a single rail 24v supply.
At this age the switch contacts will be quite tarnished and the whole select switch should be swapped out for a new one. The toggle switch may or may not need doing too.

What are your plans for it, do you have any other Naim kit?
 
I would like to getting it running and check it out. Thanks for confirming that it’s a 42.5. I’m fairly certain that it was originally paired with a NAP 110. I got it at a church rummage sale and remember seeing a guy walk off with a similar looking black box (can’t win them all)

I have a laboratory DC power supply that I’ll use for testing. If I like the results, I’ll consider building up a dual PS. I’ll give every thing a good going over. Considering swapping the BNC phono inputs for RCA.

Curious about the phono boards - are they necessary for phono operation, or are the customized for specific cartridges? The ones installed are labeled “CR322” and the board screen is 322/3.

Overall, I’m quite fascinated by this Naim. It’s very different than anything I’ve worked on and somewhat mysterious.
 
The Naim 322 boards are suitable for most, if not all, MM phono cartridges.

If you don’t need the phono input you can remove the 322 boards ( which would be easy to sell ) and replace them with wire links or link boards to give an additional line level input.
 
Slotted grub screws are best loosened with a jewelers screwdriver and it’s more difficult to over tighten with one.

Pete
 
It lives!!!

Rigged up a lab power supply and some jumpers to get power and signal to and from the unit. Also replaced the BNC phono inputs with standard RCA connectors. Doesn’t sound half bad… Tested with a CD player going into the tuner input and then played a record.

A bit hard to draw a conclusion. The Sony power amp is from the early 70s and I’ve never used it until now. Phono cart is also new, so that’s also a wildcard. Going to make some proper DIN connectors so I can test with other gear. Might move it to the LR and give the Marantz a breather.

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So, I‘m about one week into listening to this.

A few impressions:

The sound with CDs is very good - level of detail is a bit shocking at times. Going to break down and get streamer soon to “contemporize”.

Vinyl has been a bit more uneven. Some records sound stunning, others not so much. I discovered the input resistor on the phono board was 62K. I swapped it out for the conventional 47K. I have a very new Hana EH cartridge on the table that I suspect needs more break-in time.

I decided to build a dual +24 supply for this. I see enough potential to take this step. Right now, I’m using a single rail lab supply. I’ve also ordered the appropriate DIN connectors to build up some proper cables.

At any rate, this has been a fun project and I’m learning a lot about these weirdly, wonderful Naims.
 
bob smog said:
Vinyl has been a bit more uneven. Some records sound stunning, others not so much. I discovered the input resistor on the phono board was 62K. I swapped it out for the conventional 47K. I have a very new Hana EH cartridge on the table that I suspect needs more break-in time.
Click to expand...
That 62k with the voltage dividers for the front end dc biasing all equate to a 47k input resistance. There's a 470pF capacitor nearby that has a far bigger impact on modern MM cartridge impedance matching. It can happily be 220pF instead.
 
Pete MB&D said:
Stranded cat5 patch lead makes the best cables use the white from each pair for 0v.

Pete
Click to expand...

I did this years ago when I first built my NAC 62 dual-rail supply - swapping to mains cable for the power connections improved sound considerably...all IMVHO of course ;)
 
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