Neil's Secondhand Naim Buyers Guide

PHONO CARDS

When buying a second hand preamp, the seller will know whether the boards are for moving magnet or moving coil cartridges. There are 2 main types of moving coil boards; the original "S" boards, and then the "K" boards which Naim released to go specifically with the Linn Karma cartridge, and sort of stuck as the boards that people used with the Troika too. There isn't actually a great deal of difference between them. To identify the boards: with the boards oriented such that the components are facing you, and the 4 connectors are on the bottom, look at the bottom resistor that goes more or less between the two left-most connectors. If it's 470 ohm (yellow-violet-brown) then it's an "S", and if it's 560 ohm (green-blue-brown) then it's a "K". The S board has a 6800pF cap across the input whereas the K board has a 1000pF cap across the input. You can change the resistor/capacitor values to toggle between the types if you want. The Linn moving coil cartridges tend to be used with K boards.

The other thing to note with moving coil phono boards is that there have been a few generations. The current boards are Mark 5. I think Mark 2 or 3 boards were around for the longest, and these seem to be the ones you come across most. The circuit is actually the same (give or take a few trivial resistor value changes in a couple of places), but the more recent incarnations have a better layout, and better quality components (the difference between the Mark 2 boards and the Mark 5 boards is clearly audible, and in my opinion can make a very worthwhile upgrade).

It is interesting to note that the phono boards in the modern preamps (92,82 and 52) are again the same circuit, but have been somewhat re-laid out with different connector positions which enable better routing.

The Prefix phono stage is yet again the same phono stage (though the loading is 560 ohm and 470 pF I think), although they have extensively re-laid the circuit out (ie, without the constrictions of having to slot into specific connectors) and the boards are actually put inside a turntable (ie, the Linn LP12 turntable), with the boards being powered from a Hicap, Flatcap or 2 of the Supercap rails. Siting within the turntable has the advantage of allowing the arm cable length to be minimised. Even though the Prefix can be powered via the 52 preamp, I have had reports that it is a lot `better' when given its own Hicap to work from. However, I have also had a report that this is `rubbish' and you are best to power the Prefix via the 52. Take your pick.