NO AUDIO ON WINDOWS 10
i Recently downloaded windows 10 on my imac mid 2011 and I installed all the drivers using bootcamp but i can solve the problem that i don't receive sound output from imac.
Earlier Mac models
On 2011 and older models, W10 is not supported, as documented in Install Windows 10 on your Mac with Boot Camp Assistant - Apple Support. There are no Apple-supported drivers on this Mac for W10.
However, if you want support, install W8.1 (Use Windows 8.1 on your Mac with Boot Camp - Apple Support) which will provide supported drivers. You should not activate W8.1. After W8.1 is installed with all the relevant drivers, you can run an in-place upgrade to W10, which will grandfather the W8.1 drivers and allow the drivers to function properly. Be aware that using this method requires future installations of W10 to follow the same method on your model.