The MESA Bigblock 750 has a built-in overdrive channel. The Mesa M2000 has a high gain switch which can be engaged with a footswitch. The Marshall MB450 head and combo bass amplifiers have a tube pre-amp on the "Classic" channel which can be overdriven. The Ashdown ABM 500 EVO III 575W Bass amp head has a built-in overdrive effect. Overdrive is also available on many Crate bass amplifiers. The Yamaha BBT500H has three types of built-in drive effects: overdrive, distortion and fuzz. The Ampeg B5R Bass Amplifier has two channels: clean and overdrive, with the ability to combine the two. Verellen, a boutique amp company, produces a bass amplifier with a built in overdrive channel.