Neil's Secondhand Naim Buyers Guide

THE PREAMP POWER SUPPLIES

All the preamps except the 52, can be powered from the 110, 140, 90 and 180 poweramps. In this arrangement, the poweramps supply a single 24v rail that powers the whole preamp. It is less than ideal, but gets the things up and running. Note the 250 and 135 power amps cannot power a preamp.

The next step is to add a Hicap supply. This supply replaced the Snaps supply, and basically looks like half a 250 power amp. The supply is arranged with 2 separate secondary windings on the coil, with separate rectification and smoothing. The coil is around 200 VA per channel or thereabouts, with around 15000 uF of smoothing on each channel. The supply gives about 38v raw dc, which then supplies an LM317 regulator which is set at around 24v (or just above). Note that by changing the resistors in the LM317 circuit, the Hicap can give a regulated supply of up to about 33v with no problems. Useful to know for you tweakers.

A slightly cheaper version of a Hicap is the Flatcap which uses a smaller coil etc but is reported to work well by dealers. It can be used in the same way as the Hicap (ie, it offer 2 power rails at 24 v). I would not be at all surprised if the Flatcap might be very close to the Hicap in performance, but haven't tried it myself.

The Supercap can be used with the 82 or 52 preamps, though the operation is not the same for both preamps. The Supercap has a larger coil than used in the Hicap. The smoothing is done by a bank of caps (wired in parallel giving somewhere about 60000 uF total). Sitting on the power rail are a load of the LM317 regulators. Originally I thought it was 14, as that was the number given to me by Naim when I rang them up when the Supercap first appeared (guess they were having an off day). However, it turns out there are in fact 15 regs, although only 12 are used for audio circuits. Suffice to say, `lots'! I was told that for the Supercap, they used devices which are made by "Lambda" which they reckoned were quieter than other makes. According to Naim they test them and reject about 75 percent of the devices (the others are either rejected outright or else are good enough to go into Hicaps). The multi-channelled rails can go to power a fully configured 52 preamp and also the left and right sides of the Prefix phono stage. When used with the 82 preamp, I am told that only 4 of the rails are used, although one can see why a Supercap sounds better than 2 Hicaps though.