Piezo horn distorts on low frequencies

[GeoffByrne]

I've just put a monitor/cab together for various purposes - lightweight cab for practice, monitor for gigs.

I have a Celestion B200 wirede in & also a piezo horn stated as being 1.8 - 20kHz.

Works great being fed from a Carlsbro 3 channel keyboard amp - mic, bass & guitar for small rehersals. Piezo is great - however, it is quite suddenly cutting into fierce distortion when playing the bottom 2 strings of my bass.

According to what I'd read, piezos under 2kHz don't need any caps or resisitors, but obviously not.

Can someone please suggests what I can add to the circuit to keep the piezo clean, please?

G.

[Stinsok]

It shouldn't be affected by those frequencies.

[billfitzmaurice]

Originally Posted by GeoffByrne

Piezo is great - however, it is quite suddenly cutting into fierce distortion when playing the bottom 2 strings of my bass.

That's not the fault of the piezo, it's the fault of the amp. The amp is clipping and what you're hearing through the piezo are the harmonics generated as a result of that clipping. Piezos are so good at revealing clipping in this fashion that they're often employed as clip detectors.

[will33]

Piezo's high pass themselves and don't need a filter but you can still pass them at different frequencies if you want.

I'd start be putting a 4ohm, 5 or 10 watt resistor in front of it in line in the plus wire. That won't change it's filter frequency, it's for amplifier protection. The amp doesn't see a piezo as a coil with resistance.

If it's still harsh you can put the resistor across the terminals of the piezo. It then acts like a voice coil and you can put different values of capacitors in front of it to pass it at different frequencies.

Can use a 8ohm resistor so common cap values can be used. It'll work either way, just figure cap values for a 4ohm filter when using the 4ohm resistor.

If it used to work and now it doesn't it may have just blown the piezo.