The Mi-Si Crystal is designed to retrofit existing passive pickup systems to make them active. It features a battery-free preamp designed specifically to work with undersaddle guitar pickups using passive piezo elements.The preamp for this system uses Mi-Si’s custom piezo linearization scheme – allowing for the most truthful and accurate sound from the pickup.All you have to do is power up for 60 seconds using the Mi-Si Power Charger, providing you with up to 16 hours of performance time.