image courtesy of Kevin Lightner
Sold with the Axxe, the Little Brother was ARP's first expander module, and one of the first ever. It has 9 CV/gate conections, four mixable pitches ("bass, tenor, alto, and soprano"), four mixable waveforms ("brass, hollow, reed, and fuzz"), LFO speed, vibrato depth controls, and a vibrato delay switch. The Little Brother also has a pitch-bend knob with a range of and octave up and an octave down. According to Arp's advertising it is geared toward bass sounds, "A synthesizer expander with guts. Its extra voice comes in deep and low-down."
[from The A-Z of Analogue Synthesizers, by Peter Forrest, published by Susurreal Publishing, Devon, England, copyright 1994 Peter Forrest]
[More info on the The New England Synthesizer Museum's ARP Little Brother page.]