sp scientific Mark 7 prototype siren

[Whelen Rules]

Here is the old NYPD sirens from the 80s, and early 90s http://www.youtube.com/watch?v=ED3nol_lcN0 Awsome!!! only thing is that it seems it would not be as effective holding at peak like that during wail.

[JasonC]

All NYPD sirens still feature the "Momentary yelp" tone, as well as immediate cessation of a tone (i.e., the wail doesn't coast down). Many PA300's were simply rewired to accomplish this.

[Robert Gift]

All NYPD sirens still feature ... immediate cessation of a tone (i.e., the wail doesn't coast down). Many PA300's were simply rewired to accomplish this.

I like that.
I press microphone button to instantly silence Wail and avoid the 4-second coast down.
This saves the ears of pedestrians at whom the speakers will point as I am turning, plus, by that time, the siren sound is not needed anyway.

How do they accomplish immediate cessation?
Thank you,

[Justin]

By simply cutting off the current to the driver.

I'd imagine some older controllers were designed without this in mind, all you need is a new controller.

[JasonC]

By simply cutting off the current to the driver.

No.

To achieve immediate cutoff, you simply ground one of the legs of the wail capacitor (C-24?? I cant remember without looking at the PC board). I dont have my schematics anymore but I've modded several PA300's this way and even included phaser override capability.

[Robert Gift]

I slightly slowed the Yelp on our Unitrol 800 by adding capacitance.

But they would not approve of making any alterations such as a switched ground to the Wail capacictor.

If anything ever fails, though totally unrelated to the unauthorized alteration, they would void any warranty.
(But I have never owned ANYTHING which was even close to being within the warranty period!)

I just use the microphone switch.
But the sound generation circuit continues to cycle, so when I let the mic switch go, the siren emits whatever part of the cycle it happens to be in.
Example: It may be sound at the top and then descend.