# Amplifying a wireless doorbell.



## DCATTechie (Aug 13, 2008)

Im currently working on a show where we need a doorbell sound effect. We went out and bought a wireless door bell (director didnt want to run a recorded sound through the system for some reason....). The reciever/speaker is set down on stage hidden behind a plant while the transmitter/button is kept up in the booth for the SM to control. Anyway, the bell sounds just dandy when no one is talking, but when there is dialogue, you can barely hear it. So, I need a way to amplify the signal so it can be heard over talking/yelling. To make it more complicated, the director does not want to run cable behind the set so we can't mic it (including wireless because again they don't want it through the PA). My plan is to somehow get the signal to the aux input of this Anchor MINI VOX Handheld Pa System*-* Portable PA's- Complete PA Systems & Packages- Pro Audio- PSSL.com. Unless one of you has a better idea (I hope so!). What I have so far are the reciever speaker wires cut, stripped, and electrical taped to the leads of a 1/8" plug which will go into the aux input of the mini-vox. But so far, no luck, maybe the mini-vox can't pick up that small of a signal? Can any of you help me out?


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## SHARYNF (Aug 13, 2008)

typically the problem would be that that signal level is too high? One method would be to just use the mic that comes with this portable pa and keep it plugged into the portable pa and have the mic pick up the door bell sound 

sort of an odd way to do it , I am guessing the director wants to make sure the sound of the bell appears to come from a specific location on stage
Sharyn


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## BNBSound (Aug 24, 2008)

You can force the doorbell to be louder by using a speaker with lower impedance than the stock one. In a regular PA, if you switch from one 8 ohm speaker on a line to having two in parallell, the impedance drops to 4 ohms and the amplifier driving them puts out nearly twice the power. There are limits to this though.

While PA amps are designed with a range of impedances in mind and have the minimum allowable load clearly marked on them, the amp in your doorbell is likely just an opamp on a chip. While not as robust, it should be able to handle a lower impedance load for the short period of time that you need it to work.

Get out your meter and take an ohm reading of the built in speaker, you'll have to round up as the purely resistive measurement of a coil is only about 80% of what the complex impedance is (eg, 6 ohm reading from an 8 ohm speaker) Then take a trip down to Cell Phone Shack and see what they have for tiny replacement speakers. If you can find one that will fit in the box along with the original one, then use one with the same value and hook it up in parallell. That way you half the impedance and nearly double the output of the audio chip. Or, if you can find one that is around half the impedance by itself, just replace the original with that.


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## philhaney (Aug 29, 2008)

DCATTechie said:


> What I have so far are the reciever speaker wires cut, stripped, and electrical taped to the leads of a 1/8" plug which will go into the aux input of the mini-vox. But so far, no luck, maybe the mini-vox can't pick up that small of a signal? Can any of you help me out?



First of all, you want those leads _soldered _to your 1/8" connector, not taped (trust me on this one  )

Secondly, your P/A amp is looking for a signal that will drive a headset, or pair of ear buds, in the one (or more) volt range. The signal coming from your door bell is going to be lower. The main reason you're not getting any output on your P/A is signal loss caused by impedance (resistance to an alternating current) missmatch. To fix this, put a preamp in-between your doorbell and P/A amplifier.

That should fix things right up.


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