Need help connect pa siren to phone speaker

Thread Starter

Ntmike

Joined Apr 3, 2020
45
I think the telephone earphone (he calls it a speaker) feeds both stereo amplifier inputs and is used for making the announcement.
Maybe he planned to replace the stereo amplifier he showed with an expensive siren with horn speaker and 2 channels amplifier.

Here is a cheap little siren module sold on all Chinese online sites. Another circuit must be designed to activate the siren for a couple of seconds when the phone rings. Then the phone calls about Duct Cleaning and Windows And Doors can wake his wife and his entire neighbourhood.
Will his wife hang up the phone?
The amplifier shown in post #1 is a stereo amplifier with what appears to be bridging type outputs. So either channel can drive the speaker, but not both. To use the phone it will probably be most effective to connect a small audio transformer across the earphone (speaker) in the handset and then use the other winding of the transformer to feed the amplifier input. Since the microphone is an electret it will have a DC bias and a much lower signal amplitude. That is why the speaker connection is a better choice.
i have connected and all working very loud but when at loud it have some fuzzy sound in it. If i can eliminate those fuzzy sounds then it perfect. I have connected the speaker phone wire to both channels of amplifier.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
i have connected and all working very loud but when at loud it have some fuzzy sound in it. If i can eliminate those fuzzy sounds then it perfect. I have connected the speaker phone wire to both channels of amplifier.
Is there some things i can use to filter out noise at the speaker?
 

djsfantasi

Joined Apr 11, 2010
6,821
Sounds like your input signal is too strong, and the amplifier is being overdriven.

You can either get an amplifier with a larger input range. I.e., if your input signal is 0-5V, use a 9V powered amplifier.

Or you can reduce the input range. This could be a simple pot or a complex mixer circuit.

For example, use a 10K trim pot. One end connects to the common input of the amp (where one side of the audio source connects as well). The other end of the trim pot connects to the other side of the audio source side. The wiper connection connects to the remaining amplifier input terminal.

This second option is easier to test, so you might want to try it first. Once the trim pot is set, you likely won’t need to move the trim pot. A dab of hot glue will hold it in place.
 

Audioguru again

Joined Oct 21, 2019
1,918
Yes, all amplifiers including the stereo amplifier you showed have a volume control. When the volume control is turned up too high then the output of the amplifier is distorted (fuzzy sound) so turn down the volume control until there is no more distortion.
Maybe your power supply is weak and causes its voltage to drop when the output power is higher than the power supply can produce. Measure its voltage when the fuzzy sound occurs and tell us the voltage and how much it drops.
 

MisterBill2

Joined Jan 23, 2018
7,031
i have connected and all working very loud but when at loud it have some fuzzy sound in it. If i can eliminate those fuzzy sounds then it perfect. I have connected the speaker phone wire to both channels of amplifier.
Is that "Fuzzy Sound" distortion? Or noise when there is no signal or speech? The causes are quite different and fuzzy is not an adequate description.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
Yes, all amplifiers including the stereo amplifier you showed have a volume control. When the volume control is turned up too high then the output of the amplifier is distorted (fuzzy sound) so turn down the volume control until there is no more distortion.
Maybe your power supply is weak and causes its voltage to drop when the output power is higher than the power supply can produce. Measure its voltage when the fuzzy sound occurs and tell us the voltage and how much it drops.
Thank you very much. I am using a 110v to 12v adapter I will buy a power supply for it
 

Audioguru again

Joined Oct 21, 2019
1,918
OK, the fuzzy sound is noise. To find out of the fuzzy sound comes from the siren or from the phone then disconnect each one separately.

A 12V power supply will allow the bridged class-D amplifier to have an output of about 22V peak-to-peak which is 7.78V RMS which produces only 7.6W into each of your 8 ohm horn speakers. I hope the adapter is 12VDC and not 12VAC.

Maybe your power supply maximum rated output current is too low. What is it?

Please provide more details for everything you talk about.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
OK, the fuzzy sound is noise. To find out of the fuzzy sound comes from the siren or from the phone then disconnect each one separately.

A 12V power supply will allow the bridged class-D amplifier to have an output of about 22V peak-to-peak which is 7.78V RMS which produces only 7.6W into each of your 8 ohm horn speakers. I hope the adapter is 12VDC and not 12VAC.

Maybe your power supply maximum rated output current is too low. What is it?

Please provide more details for everything you talk about.
12dv at 1000ma
 

Audioguru again

Joined Oct 21, 2019
1,918
12VDC at 1000mA is 12W. The amplifier outputs are 7.6W x2= 15.2W plus maybe 3W of heat= 18.2W. The power supply will be overloaded if the volume is turned up.
 

Audioguru again

Joined Oct 21, 2019
1,918
Before buying another power supply, please post a link to the details of the amplifier you are using and tell us how much output power you want. The amount of output power is determined by the voltage and current ratings of the power supply.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
Before buying another power supply, please post a link to the details of the amplifier you are using and tell us how much output power you want. The amount of output power is determined by the voltage and current ratings of the power supply.
here is the amplifier specs I think output of 30w on each horn speaker should be loud enough
 

Attachments

Audioguru again

Joined Oct 21, 2019
1,918
Everything on the spec sheet is wrong, probably a bad translation. It says the output power is ZERO!
It probably uses a TPA3116D2 IC which is not what it says.
The datasheet for the TPA3116D2 is written correctly and says that the output power at low distortion is 32W into 8 ohms per channel at fairly low distortion when the power supply is 24VDC/3.2A.
Since it is made cheaply "over there", it will probably overheat.
 

Attachments

MisterBill2

Joined Jan 23, 2018
7,031
OK, the fuzzy sound is noise. To find out of the fuzzy sound comes from the siren or from the phone then disconnect each one separately.

A 12V power supply will allow the bridged class-D amplifier to have an output of about 22V peak-to-peak which is 7.78V RMS which produces only 7.6W into each of your 8 ohm horn speakers. I hope the adapter is 12VDC and not 12VAC.

Maybe your power supply maximum rated output current is too low. What is it?

Please provide more details for everything you talk about.
How about calling those things horn speakers instead of sirens? I had a stock of automotive alarm sirens and they are different. Calling them sirens is confusing and misleading, also incorrect.
Now for the noise in the speakers, if it is there when there is no talking then either it is the amplifier or the phone. Disconnect the wire from the phone, at the amplifier, and let us know if the noise stops.
If the noise is from the amplifier then it is either power supply noise or amplifier noise.
And there is still no useful description of the undesired sound. Is it a constant buzz or a constant hum, or a random varying sound? Without a better description there is no point in anybody giving any advice.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
How about calling those things horn speakers instead of sirens? I had a stock of automotive alarm sirens and they are different. Calling them sirens is confusing and misleading, also incorrect.
Now for the noise in the speakers, if it is there when there is no talking then either it is the amplifier or the phone. Disconnect the wire from the phone, at the amplifier, and let us know if the noise stops.
If the noise is from the amplifier then it is either power supply noise or amplifier noise.
And there is still no useful description of the undesired sound. Is it a constant buzz or a constant hum, or a random varying sound? Without a better description there is no point in anybody giving any advice.
Thank you very much. It is a hum sound when it turn on. It get louder with high volume. Maybe power supply too weak cause the humming. I ordered new supply. When it arrived I connect to the system to see if the noise go away.
 

Audioguru again

Joined Oct 21, 2019
1,918
A "fuzzy sound" is completely different to a hum sound. Any amplifier produces hum:
1) When the input wires are not a shielded audio cable.
2) When an overloaded power supply produces hum.
3) A ground loop.
 

MisterBill2

Joined Jan 23, 2018
7,031
Given that the power supply is rated for both less voltage and less current than the amplifier is listed as requiring that may be one problem.
In addition, since it seems that the input connection is directly to the microphone circuit of the phone, and because none of the phone circuit is either ground referenced or shielded, that is probably another source of hum. My suggestion to use an audio transformer and connect the primary across the ear-speaker was not just some idle rambling. It is a way to avoid picking up hum from phone circuits. I have used it and I know that it works, at least with the correct transformer, one that has at least a medium impedance of both primary and secondary.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
A "fuzzy sound" is completely different to a hum sound. Any amplifier produces hum:
1) When the input wires are not a shielded audio cable.
2) When an overloaded power supply produces hum.
3) A ground loop.
Have it all connected to 10a power purchased from amazon. The hum noise still there as soon as the amplifier turn on even without phone connection. May be the noise come from the amp itself.
 
Top