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Naxo build

N

new naim boy

pfm Member
Over the past few months I have built a Naxo from bits lying around. I had to buy a few small caps, that's all. Probably cost about £5 for bits I didn't have.

The schematics were obtained from Neil Mcbride's site. The unit consists of four identical sections, two low pass and two high pass. In each of these sections there is a distinct low/high pass module, which I put on a detachable board to allow me to alter the crossover frequency. It all fits nicely on two matrix boards from Maplins, which I did intend to use for something else. Too many projects....

Each section has it's own regulator. Nothing fancy, there are loads of 317 based regs around costing very little and which do a great job.

I have an old pair of Alphason speakers with ribbon tweeters, which I have connected to the crossover set for the SBL 3.0khz crossover.

The whole thing was a bit of an experiment. But what an amazing revelation this unit is. If anyone is interested I'll post some pics. This unit is definitely staying in my system.
 
Yes, please post pix! I've got a spare NAXO board that I've been meaning to rebuild with better components and local regs. It would be great to stir the active pot around here!
 
Here are the PSU and Naxo boxed separately, rear view.


IMGP1736.jpg


Here are the innards of the Naxo. You can see a board for each channel. On each board the regulators are in the centre, which start with a LM317 and end with a gold cap. The LP and HP circuits run vertically in this picture. There are Wima 10uf coupling caps at their inputs and outputs. In the middle of each filter circuit you can see a slot in board which determines high or low pass.

IMGP1737.JPG


The schematic for the reg that I used can be found here in post number 34.

http://www.diyaudio.com/forums/power-supplies/28978-improving-lm3x7-regulator-circuit-4.html


There are loads of different ideas around, so it's not worth much discussion. Except to say that it's cheap and very effective.


 
Perhaps it would be worth designing a PCB for just one of the filter circuits, and running a GB? So you would use 4 for a Naxo, and feed each from your own regulator. I'm sure others here may have better suggestions. I certainly would be interested in a balanced version.

However, if you have some BC550s and BC560s and a few suitable input/output caps you could make one of the filter circuits for a few quid. Cheaper than buying the PCB I would guess.
 
Actually the design of the filter power supply circuitry has moved on a bit since McBride's diagram. He must have had a really old Naxo. In recent units the two halves of the filter circuit are separately decoupled from the rail. This seems to have been a gradual evolution as my older CB Naxo had the treble filter decoupled in two places but the bass filter exactly as McBride shows it. My Snaxo has two decoupling caps per filter and uses different R and C values from McBride's circuit.

I'll capture a snaxo 2-4-2 for cheap one of these days and evaluate the differences.
 
Any body got a circuit diagram for the most up to date circuit then? And does anyone know how to calculate different values for crossover point and slope?
 
Hi PD.

Forgive the ignorance but the links seem to be for op amp circuits, unless i'm missing something?

Stefan
 
Thanks for the links PD. I'm quite happy with the 3khz crossover point at the mo, but it's good to know how to change things to get something different. I'm keen to experiment with this circuit, however. Firstly to get a balanced version and then trying to improve the buffers.
 
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