#PIEZO PICK SERIES#

IвЂ™ve terminated mine in 3.9M because thatвЂ™s what I had to hand. If that is 20Hz, since the impedance of the capacitor is 1/2 pifreq*C then you want that to be > 530k.

#PIEZO PICK SERIES#

You need to put this into a load which is higher than the impedance of the series capacitor at the lowest frequency of interest. Hence the reputation for poor bass performanceвЂ¦.вЂќДЄ piezo element can be thought of as a sound-dependent voltage source in series with a large capacitance of about 15nF. If wired to a consumer plug-in-power microphone input of about 7 kilohms impedance, the result is a 1kHz high-pass filter. When wired to a normal 50 kilohm line input this forms a 200Hz high-pass filter, which eliminates the bass. The reason why these devices often sound tinny is because the piezo sensor presents its signal through a series capacitance which is small, typically 15nF or less. However, the main reason these have gotten a bad rap is that many people couple them into a standard audio load, which loses low frequencies. This will tend to lead to a peakiness at mid-frequencies, which is why I glue these to a magnet to try and spread this peak and make the coupling to the source better. The brass disc on which the element is glued is designed to resonate at the design frequency of 2-4kHz so that a large audio output is achieved with a small power input. The sound to voltage conversion isnвЂ™t noted for its high quality вЂ“ most piezo contact mics are tuned speaker elements used in reverse.

First of all though, why do these things sound rotten the way they are most commonly used? Two solutions are proposed вЂ“ the cheap and cheerful FET buffer which probably meets all the requirements of 90% of users who are using the devices on outside structures, and the high performance version for those who want higher performance and lower noise. The pickup needs to work into a much higher impedance, typically 1 megohm or so. By their nature they can generate a lot of signal, but they cannot drive a 50 kilohm typical line input. The problem with piezo guitar pickups and contact mics is that they are not well matched to typical audio inputs. They seem to promise a lot, but easily sound rough as commonly applied. They seem to cause grief when used as contact mics. Cheap, innocent looking piezo elements do okay as greetings cards sounders.

Piezo pick