Martin Thinline Gold Plus VTI PickupItem # 18A0058 Fishman’s classic Acoustic Matrix Natural pre-amp with the added benefit of ergonomic sound hole-mounted Volume and Tone rotary controls. Features the same tried-and-true, flagship Acoustic Matrix pickup found in all of our other premium systemsHigh-quality, Under-saddle Acoustic Pickup SystemDesigned for 000 size or smaller acoustic guitarsSound hole mounted volume and tone controlsLow profile design keeps the integrity of your instrument