One main question about harp guitars, and most acoustic instruments for that matter, concerns pickups systems. First and foremost, a very useful site that does sample demos of all the main pickup manufacturers is the Doug Young website:
For those wanting a more detailed explanation of how pickups work, I will explain a little of the physics involved and some of the conclusions I have found over the years from my own testing, demos and troubleshooting different pickup systems.
Understand that there is really only 2 types of pickup (or transducer) technology, that is to convert the sound made by a guitar string into an electrical signal that can then be amplified. These 2 types are magnetic and piezoelectric. There are other types like the optical sensor used to pick up sound but I have not had a chance to test any of them.
A magnetic pickup consists of a permanent magnet with a core of material such as alnico or ceramic, wrapped with a coil of several thousand turns of fine enameled copper wire. When a guitar string vibrates it induces an alternating current through the coil of wire. This is the primary pickup of an electric guitar, that can have 1 or 2 (or sometimes 3) coils in various configurations and positions under the strings. They are made for acoustic guitars also and are typically mounted in the sound hole (See Sunrise Pickups, Fishman Rare Earth, or L.R. Baggs M1).
A piezoelectric pickup is a sensor that converts pressure to eletricity by deforming of a certain solid material like crystal, ceramic, or bone. For musical instruments, they are most commonly used as a “contact pickup” (like a stethoscope doctors use, available in various shapes and sizes, see image on left) that glues on to the soundboard of the instrument, or as a “saddle pickup” (image on right) shaped like a long rectangle strip that is installed under the bone piece on the bridge (the saddle) where the strings have the most downward pressure.
Magnetic Vs. Piezo
Differences in sound and tonal qualities are apparent between these 2 types of pickups. Magnetic pickups generally have more sustain when you pluck the string, can be turned up louder and provide a rich low frequency. As you play higher notes, the magnetic pickups tend to sound eletronic and cold. Piezo pickups are usually warmer and woody sounding all around, have more “open-ness” and natural sounds on the higher notes, pick up more “body” sound of the entire instrument, but tend to feed back on the lower frequencies if they are turned up too loud.
String Attack Vs. Signal Output
There is also a difference between the 2 kinds of pickups concerning the input signal to output voltage ratio. With magnetics it is a linear ratio, and with piezos it is logarithmic. This means that with a magnetic, if you strike the string 2x as hard, you will get 2x the output volume. With the piezo, if you hit the string twice as hard, you get 4x the output volume. So sometimes with piezo pickups you can hit the string hard enough and it will actually clip the pickup signal (before it is preamped) and generate what is sometimes called a “quack” sound. Saddle piezo pickups are more prone to this than the “glue-on” contact piezo.
So what is the best pickup for guitars or harp guitars?
The answer is not simple, as I wrote earlier it really depends upon your playing style, but mostly what does your ear like to hear? What is very popular now is a blended system which incorporates both the magnetic and piezo pickups together allowing you to adjust how much of each signal you want to hear. This does offer a great blend and tonal balance, but from an electronics perspective, it is the more difficult to deal with because of the impedance difference between the 2 signals; but there are now several types of preamps that can handle the 2 signals and give great sonic results.
Ultimately for the best acoustic sound you will never get better than a microphone. For studio applications this is the preferred method, however for live/stage applications this does not work at higher volumes, especially with a guitar or harp guitar. Bluegrass guitarists can sometimes get away with just a microphone on stage when their action is set up high and have nice loud heavy strings on a dreadnought guitar (which is why they typically use that kind of guitar and setup). For finger-style players a nice blended pickup system provides the gain and tonal needs to properly amplify the delicate attack and finesse on the strings while also allowing for each artist to adjust the blend of each pickup to achieve what his ear likes the best. The tradeoff is that this type of system (especially for a harp guitar) results in many pickups needing to be used, and an elaborate (and expensive) pre-amp.