Need help connect pa siren to phone speaker

Thread Starter

Ntmike

Joined Apr 3, 2020
45
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
Thanks, i have it all connect to the new 10amp power supply. I still have that hum noise even without connect to the phone. As soon as the amplifier turn on, there is a humming noise. I not familiar with Connect transformer to speaker. You know a specific one that i can get?
 

Audioguru again

Joined Oct 21, 2019
1,931
You did not hear me. You need to find out if the amplifier and power supply make the hum, if the hum comes from the wires and phone, or if the hum comes from the wires and siren.

1) Disconnect the two inputs At The Amplifier. If it hums then the hum probably comes from the cheap power supply.
2) If it does not hum then connect the phone's cable to the input of the amplifier. If it hums then disconnect the phone At The Phone end of the shielded audio cable. If it still hums then the cable is not shielded type.
3) With nothing connected to the inputs, connect the siren's shielded audio cable at the amplifier but the siren disconnected at its end. If it hums then the cable is not shielded type.
4) Connect the siren to its cable. If it hums then add an audio transformer between them.
 

MisterBill2

Joined Jan 23, 2018
7,040
Try using a battery. You might find that the hum goes away.
It seems that there is much more here than we know about. Hum from an amplifier, that is not internal oscillation, can come from something connected to the input, the power supply, or being picked up by the amplifier itself.
The photo that we saw was an open circuit board without one bit of shielding. So the hum might be picked up by the amplifier itself.
 

MisterBill2

Joined Jan 23, 2018
7,040
You did not hear me. You need to find out if the amplifier and power supply make the hum, if the hum comes from the wires and phone, or if the hum comes from the wires and siren.

1) Disconnect the two inputs At The Amplifier. If it hums then the hum probably comes from the cheap power supply.
2) If it does not hum then connect the phone's cable to the input of the amplifier. If it hums then disconnect the phone At The Phone end of the shielded audio cable. If it still hums then the cable is not shielded type.
3) With nothing connected to the inputs, connect the siren's shielded audio cable at the amplifier but the siren disconnected at its end. If it hums then the cable is not shielded type.
4) Connect the siren to its cable. If it hums then add an audio transformer between them.
THERE IS NO SIREN IN THIS SYSTEM!!! It is a horn speaker that is similar in appearance to a siren speaker.
 

Audioguru again

Joined Oct 21, 2019
1,931
Many translation problems;
1) His photo shows two PA horn speakers but he keeps on talking about a siren. Now is says there is no siren.
2) He shows a telephone handset and he calls its earphone a speaker. He says its speaker feeds the amplifier.
3) He does not say if somebody answers the phone so that the person calling can talk on the PA.
4) He does not know how much power (loudness) he needs.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
Many translation problems;
1) His photo shows two PA horn speakers but he keeps on talking about a siren. Now is says there is no siren.
2) He shows a telephone handset and he calls its earphone a speaker. He says its speaker feeds the amplifier.
3) He does not say if somebody answers the phone so that the person calling can talk on the PA.
4) He does not know how much power (loudness) he needs.
Thank you. I am looking into audio transformer now. The hum at the speaker. The Bojack ei-14 transformer 600:600 ohms at Amazon. You think this will help reduce the humming? Delivery for this items is about 2 weeks.
 

MisterBill2

Joined Jan 23, 2018
7,040
Thank you. I am looking into audio transformer now. The hum at the speaker. The Bojack ei-14 transformer 600:600 ohms at Amazon. You think this will help reduce the humming? Delivery for this items is about 2 weeks.
If disconnecting the cable from the phone proves that the hum is coming from the phone system, only then would the transformer offer the possibility of stopping the hum. If the hum is from a different source then it will not be the solution. And since we have no information about the rest of the system it is not possible to offer a single solution that is certain to work.
The hum may also be from the amplifier not being shielded, or from the power supply, or another connection to something that we have not been told about. The hum pickup might even be in the long speaker leads running with power wires, or even being shared with a power connection. And an incorrect connection of the transformer will result in no hum reduction at all.
 

Audioguru again

Joined Oct 21, 2019
1,931
You said, "The hum at the speaker". Do you mean you disconnected the earphone of the phone with its cable still connected to the amplifier, and the hum stopped?
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
You said, "The hum at the speaker". Do you mean you disconnected the earphone of the phone with its cable still connected to the amplifier, and the hum stopped?
Disconnect the earphone the hum still there. It increase with volume up. I am going to try a battery connection today and see if it help
 

MisterBill2

Joined Jan 23, 2018
7,040
Disconnect the earphone the hum still there. It increase with volume up. I am going to try a battery connection today and see if it help
If the wire was disconnected at the amplifier input and the hum remains then it is either the amplifier, somehow, or the power supply. Since it varies with the volume control it must be entering before that stage. So it is probably not in the speaker wiring.
The only image of the amplifier I have seen was an open circuit board, and that is certainly subject to external hum sources.
 

Audioguru again

Joined Oct 21, 2019
1,931
1) Did you disconnect the earphone from the amplifier's input cable at the phone or at the amplifier?
2) Do you use a shielded audio cable between the phone's earphone and the amplifier's inputs?
3) At the amplifier is your audio cable using a 3.5mm plug or the 3 screws?
4) Do the amplifier instructions say which screw is ground?
 
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