Sound from my turntable is veiled (like behind a curtain)

+1 ggagnon! I clean the styli on my cartridges after every side. I have used isoprophanol on the Discwasher brush for decades without any damage! The use of a cleaner from AT or LAST is a good recommendation! Before playing a side I like to apply a lubricant (Stylast). Claimed to reduce wear on the diamond stylus!

@hifiman5 The setup of the table was done by a professional.  The store where I bought my cartridge.

@lewm and @roberjerman I will definitely look for a solution to clean the styli more often.

I am convinced now to find a good phono stage, any recommendation will be appreciated, knowing my cartridge is and MC High Output.

Thank you all for you answers. 

Rob, The only Discwasher brush I know of is designed to clean LPs before play, not styli.  Discwasher makes a solution to be used with that brush that does probably contain a low concentration of isoprop, but the OP seems to have used undiluted isoprop, which is another kettle of fish entirely.  Furthermore, I think the Stylast cleaners actually meant for stylus cleaning may also contain diluted alcohol.  My point was not to use UNDILUTED alcohol to clean a stylus.  But above all else, I think dirt on the stylus is not the primary cause of the veiled sound, maybe a contributor but not the major issue.

ggagnon, There are dozens of highly touted phono stages in the under $1K cost category.  Unfortunately, I have heard none of them and cannot help.  I was fairly convinced by Michael Fremer’s review of it that the iPhono2 must be very good, for $500, and handles LOMC cartridges fine.  You’ll get dozens of other suggestions.

@lewm The alcohol I used was 70%, so it is not pure.  But I will follow the advice of using special solution.  I didn't think that could damage the styli itself, I was very careful to not put alcohol on the cartridge plastic casing.

I agree a nice phono stage is needed, but have you checked the manual for your current pre? It sounds like the pre could be misconfigured for the cartridge.