Hi all,

Here's the existing circuit I'm dealing with.

Apologies for grainy pics ahead of time. I understand that what I'm dealing with is a driver for the transducer, but my question is what the components do in order to create the "siren" effect of variable pitch. Ideally, I would like to convert this to a single tone siren. I could just order the right thing OTC, but I do enjoy tinkering.

Would changing out resistors to a single value accomplish this?

 

Without a schematic or at least a close up of what the circuit is, the best we can do is guess. My guess would be that the IC is this http://pdf1.alldatasheet.com/datasheet-pdf/view/228994/ETC2/M3561.html or something similar which takes care of all the frequencies. The transistors are probably just amping up the gain to drive the speaker. In short, you wouldnt be able to change the tone if this was the case.

 

ah, this makes a lot of sense. I may try fiddling with a couple NC/NC pins I see and see if that changes the tone. I'll also draw up the schematic tonight after work.