For information on 7-string guitars, see the equivalent section in M3 Guitar 2.0.
You can take any electric 6-string guitar, get hold of a set of strings in the appropriate gauges, and tune it in major thirds. No modifications are necessary. There is only one thing you have to be aware of. Since the strings on the M3 are tuned to lower pitches than the conventional tuning the overall tension is greater than the guitar is designed and adjusted for. On most of my guitars that causes the neck to bend upwards ever so slightly, thereby making the action (the distance the strings are above the frets) too high. There is a simple remedy for that: tighten the tross rod. It is a standard procedure which is easily applied to almost all guitars, and it is described by plenty of other people (see for example Carvin Truss Rod Adjustment). You make the adjustment by turning the truss rod nut with an Allen key (usually supplied with the instrument when you buy it). For the M3 you will probably need to turn the truss rod nut clockwise by approximately 1/4 of a revolution, possibly more. Start with a small turn of 1/8 of a revolution, and leave the neck to settle for 15 minutes or half an hour before you judge the effect. I am not an expert on the issue but conventional wisdom says that wildly overdoing the tightening, so that the neck bends backwards and gives you buzzing everywhere, is extremely bad. You can ruin the neck that way. When you eventually loosen the truss rod again, the neck might no longer be straight. So take it easy at first. For the same reason, you should never leave your guitar without strings fitted because the lack of tension causes the neck to bend backwards. My guitars tend to change with the temperature and weather so I frequently have to adjust them anyway.
I have managed to break the truss rod of a cheap Harley Benton guitar while tightening it to make the neck straight. I have made the same adjustment to approximately 15 guitars, and it is the one and only time it has happened to me. If you want to play it safe, use a light set of strings that don't increase the tension significantly.
I use 7-string guitars, mainly for recording, in two specific cases. One is when I need a classical guitar with nylon strings. The missing four semitones in the top are difficult to compensate for because the body of the guitar makes it hard to reach above the 12th fret, and I very much like the sound of the high E-string anyway. The other is when I need the heavy sound of the notes below the low E. I then use a 7-string tuned from low C to high C, and the Kramer Turbulence is excellent for that. With 36 frets you are not going to have a problem getting to the high notes!
|The Giannini GWNFLE/7||The Kramer Turbulence R-36|