I dont agree with Douglas
This has been pondered on a few forums and over a few other brands as well as nad... i'll try and summarize. ... sorry this might get long...
The classic older nad 3020's from the 1990's seemed to use Japanese capacitors like Matsushita caps (now called Panasonic)
The OP is right the KSC caps. these are known failure points in TV's in things like tv power supplies and other places. the caps tend to drift greatly in value and become electrically leaky and fail.
in addition, the 2007 manufacturing date falls in the range were a lot of bad caps were produced out of China and Taiwan from about 2001 to 2010. this effected not just audio but computer electronics, with many faulty of capacitors.
The cause of the faulty capacitors was in fact due to poor industrial espionage, a mis-copied electrolyte formula. In 2001, a scientist working in the Rubycon Corporation in Japan stole a mis-copied formula for capacitors' electrolytes. in that same year the scientist's left China, stealing again the mis-copied formula and moving to Taiwan ... needless to say this formula got used by many manufacturers and caused a lot of problems. search "capacitor plague" to learn more.
The particular caps used in NAD gear are SS and NP series 1000 hour and GS and GL series 2000 hour lifespan caps in both the power supply and audio sections. They are the lowest grade electrolytic cap KSC makes . KSC has now removed their specification for these caps off their website however you can see some of the specs here
http://www.paullinebarger.net/DS/KSC [King-Sun]/KSC Series Table PARTIAL.pdf
NAD itself has an interesting history, after the success of the 3020 in the 90's they fell on hard times, and were sold twice. it has been speculated that the use of these cheap capacitors was part of cost cutting measures and not a technical choice.
nad has been manufactured in Asia for a long time. i think the 3020 was made in taiwan, and the OP amp was made in china. remember the faculty that manufacturers the item dosn't choose the parts, nad does so you cant blame the use of Chinese caps on the manufacturing facility..
i think most engineer types find it hard to believe another engineer would spec off brand Chinese caps in their design, thats why its belived to been a cost cutting measure.
Some say a cap is a cap and one cant tell the difference between different caps asuming all other parameters are equal... and others say there is a huge difference. obviously ESR and leakage ratings of new caps will have an impact on a giving circuit. i am not going to get into that Frey, however, when capacitors become electrically leaky and/or change value it going to have an impact. So even if it rolls out of the factory sounding pretty close to what it would with high quality caps, over time that will change.
Unfortunately, without comparing the sound your amp against another one, or being able to measure the sonic effects of the caps, its hard to just turn it on and have a listen and tell if there is a problem or if a cap is close to failure.
if your amp is from 2007 and has any significant use on it, the caps are getting close to or past end of life. plenty of tv's using KSC caps of this type have gone "poof" as the caps let go in the power supply and are a lot newer then your amp or experienced other problems where KSC caps have been used.
This problem isn't just KSC but many Chinese off brand caps have bad quality cntrol and/or had issues with the bad electrolyte formula. This is not to say some Chinese caps can not last a long time.. but which ones.. its like playing Russian roulette. It is true that Electrolytics do not last forever, however, Chinese caps have show themselves to be exceedingly unreliable.
if it were me id first change out the caps in the power supply. those will have had the most stress, and, will cause the most problems if they let go. it probably goes without saying if your gonging to bother doing the work, get high quality high life caps with low esr were necessary and high heat at least 105c ... the ps is were the caps are more likely going to be exposed to heat and lifespan is greatly effected by heat, see cap data sheets to get more on that.
as far as the caps in the audio path. those that have changed them out for audio grade caps from Panasonic or nichcon for example, have reported a sonic difference. it is hard to tell if it was from off values, leakage or just the structure of the new caps but i’ve never read a post from someone who said they did not hear a positive difference. Not all caps in the audio section are in the audio path so take that into consideration when selecting caps.
everyone has their "favorite" capacitors .... some say you can somewhat tailor the sonic footprint of the amp by your choice of capacitors. there have been some tests on this, one i can recall is here
High End Audio - Electrolytic capacitors though there are others. Note though, some of the results of these tests are more subjective then based on measurements. and obviously are influenced by the circuit they were tested in, and the giving esr and leakage of the cap under test etc.. so your mileage may very.
as far as the renaming caps, the polypropylene and ceramic caps, usual these are just fine and no need to change them out as they have a long lifespan, even the cheap chinesium ones
So, if the question is, should you change out the electrolytic, i think i have given come compelling reasons to do it.
personalty, i am not one to just sit on a ticking time bomb. Especially if its a piece of gear i like. There is no excuse to not do it unless you cant afford the parts or you don't have the skills to do it yourself.
hope that helps.
