Police Siren Stompbox.

[Buzz]

Hi guys!

I'm interested in making a specific pedal controlled effect.

What I want is a police siren. Engage the pedal = siren with no guitar signal. Dis-engage = true bypass guitar signal only.

Here is where I'm hitting a problem. There are plenty of 555 timer police siren circuits on the net. Sweet. I've got some of those chips I'd like to put into active service.
All the circuits I find seem to assume I'm using the circuit to run a speaker eg.

http://amplifierlab.com/wp-content/uploads/2010/06/555-Timer-Police-Siren-Circuit.png

So I can figure out the switching, no probs. But this is going into a guitar amp, not driving a speaker. Could I use that circuit as is, or should I put a buffer after it?
Would a trimpot attenuator work?

Anything else I am overlooking?

[Seljer]

The 555 timer is putting out a full square wave, at it's full supply voltage (so jumping from 0 to 9V on a 9v supply!)


I'd replace the speaker with let say a 10k resistor, followed by a 1kiloohm potentiometer for a volume control.

[GibsonGM]

The 555 timer is putting out a full square wave, at it's full supply voltage (so jumping from 0 to 9V on a 9v supply!)


I'd replace the speaker with let say a 10k resistor, followed by a 1kiloohm potentiometer for a volume control.

+1     You can run all of this stuff into your amp, no sweat, but do have to pay attention to what the output levels will be!   Seljer's idea should work fine, use any pot at hand, and start QUIETLY, ha ha.

[Mark Hammer]

You're missing the most important part: the dual-LED (blue-red) flasher that you have to put on your head when you turn the siren on.  The wires from the pedal to the headpiece are a real nuisance, though. 

[deadastronaut]

^ indeed..

buzz you will have to have these on it by law...

https://www.youtube.com/watch?v=1_wBtwKb37c

[R.G.]

There were a couple of pedals back in the late 60s that included distortion, wah, and a siren. At least one threw in "hurricane" and "surf" sounds as well.

Hmmm... found it: http://www.dirk-hendrik.com/temp/shin_ei_hurricane.gif

The siren section is in the upper right corner. I think just the three transistor circuit and the volume knob plus switch would do it.

[wavley]

You need a dub siren.

I don't see why you can't just use a 1/4" jack instead of a speaker, if your circuit doesn't already have a volume control just throw a 100k pot at the end and keep the levels low.

[duck_arse]

buzz, if you think you might like to add a "bomb drop", among others, I have a couple of these you can have ....

http://home.comcast.net/~johnselex/76488.html

[PRR]

> into a guitar amp, not driving a speaker.

Most speaker signals, you just knock-down to get Line or Mike level.

In a few cases, you need a dummy speaker to keep the source happy. Little-stuff, a 1 Watt 10 Ohm resistor will usually be ample. (If you are a part-Watt builder, try five 47 Ohm 1/4W in parallel.) Hey, probably can't hurt.

> should I put a buffer after it?

Signal is "too strong". Buffering is for weak signal. All you need is some reasonable signal loss, passive, couple resistors.

Simon's 10K fix into 1K trim is as good as any. The 10:1 ratio gets your 9V signal down near 1V. The actual resistances can vary over a wide range. If you have a 10K pot in your pocket, find a 100K fixed resistor, that'll be OK also.

[electrosonic]

I always wanted to be able to cover "Squad Car" by Eddie and the Showmen and do it right - a siren is essential.

A friend of mine used to have a 12 volt air raid type siren mounted on the underside of his volkswagen van. I wished I got it off him before he junked it.

Andrew.

[Buzz]

Thanks all.

I'll go with the 10k resistor 1k pot.

Mark and Rob. I'm too worried about shorting the flashing head LED. Too hard to mount on my tinfoil hat

RG. Wow, great circuit! I've put it into my to-do folder. At the moment I'm grateful to use some of the 555 timers that have been sitting in my drawer for several years.

Thanks for the offer duck. Going the 555 route though. Might take you up if it's too crappy though.

Paul, I assumed the buffer would work either way. Like taking a too small or too big signal and pushing out something around line level. Back to the books for me on buffers  Even if it did, it would be a complex solution to a simple problem.

[PRR]

> assumed the buffer would work either way.

It can. But when you want "smaller", you do not need the complication and power of a "buffer".

Let's look at two situations.

My old-old Jeep had manual steering and it was a beast. I needed "more". The solution would be Power Steering, with a pump on the engine and a gizmo in the steering linkage to multiply my puny 10-pound arms up to 100 pounds force.

Pat's newer Jeep had the power steering. Musta been from the Cadillac. It was TOO MUCH. Just blink and it would efortlessly drive me off the road. Don't need no added pump, it pumps too good already. Conceptually, what was needed was a restriction in the pump, so the pump would not work so good. And a restriction (crimp in the pipe, or partially closed valve) is a lot cheaper and less messy than adding pump and gizmo.

Buffers and amplifiers make weak signals stronger.

Attenuators make strong signals weaker. And are usually far cheaper than a buffer/amplifier.

Here we have like 9 Volts which can drive 1K Ohms. What we need for amp input is a Volt os less at 50K or more. If you rough-calculate the Power, we have 81mW available and need 0.02mW. We have *4,000* times more power than we need.

(It's like Pat's Jeep had the power boosted controls from the massive Spruce Goose transport airplane instead of just a Cadillac.)

[Buzz]

Thanks Paul. Well said, as usual!