This updated version of the Synthesizer 12 was introduced in 1974. The old 901 style oscillators have been replaced by 921 style oscillators. The 903 noise source has been replaced by a 923 noise source which includes a passive low-pass and a passive high-pass filter. The oldest noise source, the 903, had a single output jack for white noise only and no other controls. The 903A included pink noise. I have always likes the look of the 907A, which is turned sideways compared to the original 907 (which required four, instead of three, panel spaces).