Need help to make telephone tap coupler schematic

[eggybot]

Hi Guys,

I would like to request help if anyone can help me to figure out on this schematics for a phone tap where I can get the source sound coming from my phone to tap and convert to mic jack. There are products like this one in the market but the voice and sound coming from the phone was combine, I just want to get the sound from the caller and not the sound coming from my phone mic.

(above is the available product I see on the market.)

Do anyone can help me to give me the schema on how can I create this one, also if possible to include t he parts needed so I can buy it. I will use this on my school project to demonstrate the software that my classmate doing to capture and record the voice from phone to computer/mobile phone.

thank you (TIA)

 

[davenn]

Mabuhay

I just want to get the sound from the caller and not the sound coming from my phone mic.

then you need to tap into the audio line going to the earpiece of the phone

 

[Audioguru]

The phone has what is called "sidetone" for you to hear the loudness of your own voice. To cancel the sidetone you must mix the inverted and amplified mic signal to it.

Here is an intercom circuit that uses a transistor to make the inverter and mixer but it does the opposite, it cancels your mic signal from playing in your speaker and causing acoustical feedback howling:

 

[eggybot]

Hi guys,

thanks for rep,

@davenn
Yes, I just want to tap to the the earpiece on the handset of the phone.

@Audioguru
Sorry but it so much complicated to me for the intercom schema you post.

I have small diagram photo where you can see my plan to tap on the RJ9 wire of the handset of the phone. but the problem I'm not sure which parts I need to boost the signal from earpiece as well if the tapping of wire is correct just to extract the sound.

thanks,

 

[Colin Mitchell]

Just cut one wire and put a small speaker in the cut.

 

[eggybot]

@Colin Mitchell
will that produce noise by splitting it? also I need mic jack input so I can connect my pc or mobile.

thanks,

 

[Colin Mitchell]

Put the mic socket across the speaker

 

[Audioguru]

The telephone earphone speaker produces sounds from the caller PLUS sidetone of your own voice (so you can hear how loud you are speaking). If you don't want sidetone then you need a circuit like I showed to cancel it.

Mic jack to connect your pc or mobile? The level of a mic is VERY low so a normal line level from an earphone speaker must be attenuated to feed the mic input.

 

[Colin Mitchell]

20mA across 8R is 160mV

 

[tedstruk]

disconnect the phone receiver mic, and tap into the phone receiver speaker

 

[eggybot]

@Audioguru
Hi, you are correct, sorry if this might confusing but I want to tap earpiece sound to extend with a mic jack output where I can hook it to my PC mic/jack to capture the sound from the caller.

@Colin Mitchell
thanks

 

[Audioguru]

To feed the earpiece signal of a telephone to the mic input on a pc then you must isolate them with a transformer and attenuate the signal down to mic level that is much lower than earpiece level. The mic input on a pc is designed to power an electret mic so a coupling capacitor must be used to block the DC. Will you accept having your own sidetone or will you add a circuit to cancel it?

 

[eggybot]

@Audioguru
Thanks, I want my sidetone to be remove and I justwant to isolate the sound coming form earpiece of the handset of the phone to out in mic. Do I need at least 500Ω to 600Ω for the transformer? I have this old item from my friend and when I open it it uses capacitor and transformer but I'm not sure the numbers needed for those 2 http://www.screencast.com/t/HWneh9Lht

thanks,

 

[Audioguru]

A 600 ohm transformer would connect to a 600 ohm telephone line but we do not know the impedance of the handset on your telephone so a higher impedance transformer can pick the signal from the earpiece and attenuate it. You must add a cancelling circuit to the telephone to cancel the sidetone but we do not have a schematic of the telephone to do it.

 

[eggybot]

@Audioguru
in your best guest what capacitor ohms should I get? I will try to create a schema later and test it by tomorrow once I got all parts I need.

thanks,

 

[Audioguru]

A capacitor passes AC and blocks DC. It has microfarads, not ohms. Why do you ask about a capacitor?
An audio transformer is needed to isolate the telephone system from picking up loud mains hum from the ground on your pc.

 

[AnalogKid]

Why do you ask about a capacitor?

You started it, talking about a 600 ohm transformer. Did not. Did too. Did not. Did too...

I think the OP does not have a grasp on reactive concepts.

ak