Need help from the electronics genuious's re: petentiometers

[code3media]

Ok I am going to try an describe my question and hope somebody understands and can provide me with an answer.

I called Unitrol/Federal Signal today and had them fax me a schematic for wiring a PA mic into a 80K siren/PA. In the description, it says add a Pot or Petentiometer in the audio circuit. Problem is that they did not give me a value or resistance rating.

I went to the electronics shop and picked up various Petentiometers with different ratings. 5k,10k,25k, and 2.5 meg.

If I want to change the volume or Gain levels, which would be the best one to use? Which has the best coverage of resistance? I know that one of these will only give me a small spectrum of gain, and some might exceed the gain spectrum.

Hope this makes sense. Any help would be appreciated.

Ryan

[jim]

We need more info than this, such as amplifier sensitivity (in mV), microphone impedance and peak volatge when driven at a normal voice level.

Without this, I'd assume a 10K "audio-taper" pot will work installing it in "L-pad" configuration with the audio being applied on pins #1 and 3. Take audio off of the pot at pins #1 & 2 (or 2 & 3 if you want the pot to operate in reverse).

[wa2zdy]

Agreed, the 10k pot should do the job well. Connect the wires to the input of the amp to the end connections on the pot, then the mic to one end and the middle post on the pot. If it works the wrong way, move the wire from the mic from the one end post to the other.

Good luck.

[Microwave Mike]

The 10K log pot is a good choice for low level, high impedance, input control. In fact that is the right place to control audio.
Mics run around 150 ohm in impedance, outputs from amps run from 4 ohms to 16 ohms. A L-pad with the proper power rating would work for that. If you are going to control a non amplyfied mic a 1K log pot should work.

Note on most /\/\ radios the audio out is 16 ohms balanced. You can't ground one side. If you need to tap off the speaker out, use a transformer. Don't forget to load the output with a resistor.

MM

[code3media]

The 10K worked great, and I am all set thanks to your help.

Thanks again.

Ryan