advertisement


Naim nac 90/3 hissing

Markduc

Member
Evening
My power amp recently started hissing/ humming through the speakers after the hot couple of days even without pre amp connected
So I had a look inside expecting to see damaged capacitors
All look fine apart from the silver coloured one’s (see pic)
Looks like lcr520/ 100p/ 630vdc
Could someone confirm that they look damaged
Maybe advise on a replacement for the 5 of them
Thanks
 
Postimage or similar is your friend, but it isn't likely to be these as they will be polystyrene, which although melts easily, won't be affected at ever above normal operating temps. It is more likely to be due to small electrolytics that have finally expired with the heat. Not familiar with the amps unfortunately.
 
Before worrying: - connect the preamp (power-up the pre first) and try again.

The low output impedance of the pre (or, if you fancy, just shorting the input pins to signal 0v) will result in significantly lower noise, becasue it appears in parallel with the input resistor in the power amp (an unavoidable-architectural feature of any PA)

Without a source connected of low/near-zero impedance , any power amp 'sees' that input impedance as a thermal noise source. If that is, say 22k (I don't have figures to hand for nap90) then compared with, say, 100ohms from an active pre - which effectively shorts that 22K , but obvs comes with a little noise of its own subject to the full gain of the power amp (around 30x in round numbers) ... /scribbles a bit/...

... well you might expect as much as +10 to +20dB noise from the power amp, with 'open' inputs!

And yes, that will be very clearly audible.
 


advertisement


Back
Top