ARP 2600. Vintage Synth Explorer. "2600P v3.0: After a short run of the v2.0, a few more internal changes led to the 2600P v3.0 which switched to the 4027-1 VCO. These new VCO chips were noisy and did not sound as good as the previous chips. The rectangular Tonus ARP logo was replaced by a new G-clef ARP logo which is often used to distinguish these newer 2600's from the previous models version of the 2600P. Also, the front panel was made a little taller, providing some extra room along the very top and bottom of the front panel. The 2600P v3.0 was produced from 1972 to 74 and is the most common model.”, “2600P v4.0: A new duo-phonic keyboard (Model 3620) with LFO was introduced with the 2600P v4.0 in 1974. It also has the new G-clef ARP logo."