Troy, here are some ideas:

The PA may have a low impedance input, so that the mismatch is causing
      most of the signal to be lost.

The 10K transformer being fed by a 5 volt signal is going to produce quite
a back-emf  when the magnetic field collapses as the voltage changes from 5
volts to zero.  This pulse can 're-program' your data direction (tris)
register so that the pin is now an input.    Replace the transformer with
perhaps a 5 K Ohm resistor in series with a 0.1 uf ceramic capacitor
between the pic pin and the center of the 1/4 inch plug.  Try resetting the
data direction on the pin each time before you write to the pin.

The transformer is bad?  check the winding with an Ohm Meter.

The frequency you are using is too high for the PA system?

The output duty cycle is not 50-50?  If is it 99-1 then the piezo might
resonate, but the PA might produce nothing you can hear.
----------------------------------
At 10:20 PM 4/19/98 -0500, you wrote:
>Hi All,
>I have a question about using a PIC 12c509 to produce a steady tone.
>I wired up a simple circuit that uses a normally open switch on input
GPIO0 and as long as the switch is pressed the PIC would produce a square
wave out GPIO2. I connected a piezoelectric transducer to that pin and
everything worked fine. (I was proud of myself) I then replaced the
piezoelectric transducer with a 10Kohm to 10Kohm impedance matching audio
transformer and connected this to the input of a PA system through a 1/4
inch jack. The response was "Nothing came out of the PA". Where is the
problem? Is the 10K too high? Is the 5v square wave not enough amplitude?
Any help would be great.
>
>Troy Powledge
>TCo. Systems
>tpow@eramp.net
>

Regards,
  Ron Fial