SMSCOM Hybrid Pro 4 Amp Mk2 Fan Speed Controller

Works very well and is very quiet . I have used the cheaper model and it was noisy. This one isn't . well worth the investment to quieten things down.

I have one of these I bought from my local grow shop, I only paid £250, so I would shop around. It is however an amazing piece of kit and I did buy two because they are so good.