Sound — 9
The EMG 81s are a classic pickup. Though a lot of people seem to think they were made for high gain, in actuality their dry, balanced tone was originally geared for jazz players who wanted to have supreme articulation and let the tone come from their fingers. Upon playing the EMG 81, it's very obvious this is the case. The flat response of the pickup compared to the warmer sound of more traditional passive pickups means that every detail of your playing will come through - and for some players, this is not ideal, as any sloppiness in your playing will become much more obvious playing with this pickup. Generally speaking, the EMG 81 has a balanced, slightly nasal sound with a smooth midrange, tight low-end and crystally highs. This response makes it ideal for finger-picking, where the nasal sound is diminished slightly, as well as for playing in higher-gain settings where clarity and articulation are key. The tightness of the pickup translates into extremely clear, precise distorted tones where other pickups would get muddy. This also makes it ideal for recording and live use, as it requires less EQ tweaking to get sounding right in a band/mix, but at the same time this can make it sound slightly unappealing played on its own. Additionally, if you play with effects, such as chorus, the flat response of the EMG 81 is actually a big benefit, as, like with distortion, it won't get muddy. Unlike most pickups, due to its weak magnetic coils and active preamp, the EMG 81 is almost free of any hum whatsoever - any you hear likely comes from your pedals, cables and amp, not the pickup. The bar magnet design also means you won't get volume fluctuations when doing bends, adding to the overall consistency. Some people tend to claim the EMG 81 is an extremely high-output pickup with an overly compressed and sterile, almost "digital" tone. While it does not sound like a traditional Vintage pickup, most people who make these claims likely have not taken the time to use their volume or tone knob. A lot of the "sterility" can be knocked down to provide a warmer sound, and turning the volume down also gives the pickup a more traditional, open tone with less compression. As mentioned above, it is also less for giving of mistakes which means that you may have to adjust your playing style to get along with it.
Overall Impression — 9
I have an EMG 81 in the bridge position of my LTD MH-1000FR, which came installed with the guitar. I play primarily rock and metal, and the EMG 81 is precise and articulate for those purposes, providing crunchy rhythms, as well as screaming leads and vibrant pinch harmonics. Turn down the tone and volume down slightly for more Vintage hard and classic rock tones. However, it also delivers sparkly cleans, which are greatly enhanced by reverb, delay or chorus. For jazz, rolling the tone back a little also gives you a great, precise, neutral tone. While I would not use the EMG 81 to play blues, funk, or most pop, it can get the job done with these styles as well, with a bit of tweaking. If you are dead set on a Strat or Les Paul tone, the EMG 81 simply does not offer that, but if you are comfortable with something a bit different it is more than capable.
Reliability & Durability — 10
EMG pickups, regardless of sound quality, are world-class pickups and some of the most solidly constructed ever. Housed in epoxy for protection, they are virtually indestructible in any standard playing situations, and aren't prone to bits of hair, dust, etc. That some more traditional open-coil pickups are. Sure, an EMG 81 wouldn't survive a nuclear bomb, but due to the casing I trust its durability more than just about any other pickup. It is worth noting that, as active pickups, EMG 81s require a 9V battery to use. Reasonably speaking, you can get about 6 months of daily playing out of a single battery provided that you do not leave the cable plugged in when the guitar isn't in use. The active system also might require more extensive re-wiring or even cutting new chambers into your guitar for installation. This can make them inconvenient for amateurs to install on guitars not outfitted for active pickups.