I can't help contibuting to a thread about my favorite obsession: Sigma guitars. In the late 1960's there was a strong increase in demand for guitars in the U.S. Martin could not increase production of U.S. made guitars because of the time lag imposed by the need to season hardwoods. The Japanese manufacturers, having saturated their domestic market early in the 1960's, had abundant stocks of seasoned wood on hand. Martin began selling the Sigma line of Japanese made guitars in January of 1970. Sigma guitars made in Japan from 1970 through 1979 can be distinguished by a headstock logo consisting of the single word "SIGMA" surmounted with a greek letter sigma ("sideways M") and an inner paper label giving model and serial numbers. These early models are almost always solid wood guitars, and tonewood of a high grade at that. The early models are encoded by size, wood, and quality-grade number; that is, a DR-7 (the top of the line) is a rosewood dreadnought of top grade, the DM-5 a mahogany dreadnought of lesser grade, and so on. In 1980, the model lines and designations were changed to capitalize on Martin model names: the DM-18, DM-19, DR-28, DR-28H, DR-35, DR-41, DR-45. But the older model types were also continued as well. The headstock logo was changed to the present day form ("SigmaGuitars / EST. 1970"). The models made between 1980 and 1984 in Japan are almost always solid top with laminate back and sides (like Shannendoahs), as the Japanese manufacturers had used up their stock of seasoned woods by 1980. The paper labels were dropped in favor of stamping the back brace. In 1984, production was shifted to Korea, and in 1993-4 to Taiwan, where it continues to the present day. In general, the quality of the guitars declined in Korea to a medium or lesser grade level. A few Taiwanese (like the DR-28) are surprizingly good, but they're rare. It is worth noting that all the currently produced Sigmas except the DR-41 are designated with the quality grade of 1, meaning there is is no lower quality possible, a curous honesty on Martin's part! Which old Sigmas are worth buying? Here's a guide. The most desirable vintage Sigmas are almost any of the "old logo" Japanese made models: the DR-7 (a D-21 clone), the GCR-7 (a rosewood 00-21 clone), the DM-5, the CR-7 classical, the DR12-7 12-string. The first Sigma catalog (1970) also shows a DJ-7, made of jacaranda or Brazilian rosewood, but I know of no one who has ever seen one in the flesh! Secondly, 1980-84 Japanese made DM-18, DM-19, DR-28, DR-28H, DR-35, DR-41, DR-45 are all excellent guitars but are sometimes inconsistent: 1981-83 DR-41's are laminate; the 1984 DR-41 was solid woods! Where they are laminate construction, the veneers are of high quality and it's often hard to distinguish their sound quality from solid wood. (When in doubt, remove the end pin which will expose the edge of the side wood to inspection.) In 1980, Martin produced 100 Anniversary Sigmas (model 10), a solid mahogany dreadnought; equip one of these with a brass or ivory saddle, ebony bridge pins and medium strings and you can hunt down D-18's in the heaviest brush and stomp them to death --- it's a very loud and impressive guitar! In 1981-82, Martin produced a small number of models labelled "MartinSigma / USA" and designated by an "N" at the end of the model name: DR-28N, DR-35N, etc. These were made in the Martin factory in Nazareth, PA. If Martin makes a Martin clone in the Martin factory with Martin serial numbers stamped on the neck block, does the word "clone" have any meaning anymore? They are just re-labelled Shannendoahs, a pretty good guitar. The DR-7 model was also continued through 1980-84 in Japan, with the addition of a DR-9 and DR-11, all made in very small quantities. They sound about as good as an average Martin D-28 of the same time period (not their best period, I admit). Also made in small numbers in 1979-81 were Sigma models with the prefix 52S, as in 52SDR-7. Curiously, they are made entirely from some very strange laminates. The 52S series were sold as "professional" instruments; they have a pure clean resonant tone (like a high-end maple Gibson) which combines well with the human voice and records cleanly without a fuss. (I've had three of these, and all had thoroughly rigid construction, dead straight necks that had not moved in 25 years, low fast action, and great playing ease, as well as fine sound.) I have have owned, played, bought, sold, traded about 30 Sigmas, which include most of the models mentioned above. Because the high-quality Sigmas were made in small lots by a variety of Japanese manufacturers, there is considerable variation from one instrument to another, not in quality but in character. I have two 1980-84 DR-7's. One sounds pretty much like a slightly sweeter version of a D-28. The other sounds like a 1930's Custom Shop guitar (like that B&D Senorita that keeps popping up or an old Vega). My first "bought new" guitar was a Sigma DR-7 purchased in March, 1970 from a Martin dealer and one of the first 100 Sigmas sold. (Martin shipped exactly 100 Sigmas to dealers in 1970!) It cost $139.95 plus tax. It sounds better (to me, at any rate) than all the other Sigmas I've owned, save one. It has a number of construction details not in common with later DR-7's, so it's possible that it would be worthwhile to search for the lowest serial number when shopping for a DR-7. If by the Martin sound, you mean (and most people do) that crisp percussive snap of attack on the bass strings, the only Sigmas that approach that particular quality are the early DR-7's.