A really big transformer and filled with A-class parts with a big ALPS volume controle accounts for the 14 kg of weight. It's a real big amp with lots of power and smooth silky high's and never gets harsh. Very detailed and refined sound in contrast to the functional rugged design. This is a true beauty sound wise and if you can get one, go fir it! This amp needs high resolving speakers to show whats really under the hood!