diy tips & tricks
Naim NAC Series Pre-amp
A really simple yet effective mod for NAC series pre-amplifiers. The 62K (R2) resistor biases the 'ring of two' current source and carries transient disturbances from the +24V supply rail. Adding a 4K7 resistor plus a 47uF cap then changing R2 for a 56K to restore the equilibrium, takes the treble 'rip' out of the sound - so reducing audible aberrations by a considerable margin and making the whole performance more 'listenable'.
The 'ultimate' mod added recently takes the 321 stage to entirely new heights with the addition of 'gyrator' or VBE multiplier regulation instead of the RC series dropper. The pass transistor TR6, may be any low noise NPN such as BC546 etc. Extra decoupling for the voltage stages (47R + 100uF & 120R + 47uF + 100n) and the replacement of the resistors shown by RC55 high definition components reaps dividends.
Experimenters may care to substitute a J510 (3.6mA constant current diode - selected for lowest noise), instead of the 56K bias resistor. The 47uF feedback capacitor may be changed for an Oscon SG/SP series of similar value for a cleaner, crisper sound. The 10uF tantalum at the input may be changed for a 1uF PPS ( Polyphenylene Sulphide - Evox SMR ) film cap for a noticeable improvement in resolution - bass roll off is slight. The output cap may be a BC 128 series solid aluminium or an Oscon SP series, stay with10uF……………..more later……….
This gentleman seems moderately pleased with his efforts:
" Today I did your recommended tweak on my Nac72. I was totally astonished to hear a completely other amp (I didn't expect that much). It's like the step when you add a hicap. In this moment I listen to a CD with old Curtis Mayfield music and it sounds nearly like from vinyl! REALLY amazing! " - Stefan Gruenenwald - Leipzig
