Good morning!
First post here so please be gentle! I'm in the process of building an intercom system for my car, using the Peltor headset mentioned on the subject. As a newbie to all this it's proving harder than I thought.
The system should also be able to use normal smartphone type headsets. This part I have more or less sorted by using a TPA111A2 headphone amp to drive them and a simple NE5532 based electret preamp.
Back to the Peltors. These have a TP-120 TRRS connector, Tip + Ring1 are for the mic, and Ring2 + Sleeve are for the phones (L+ & R-, R+ & L- respectively as it only plays mono signals). The only way I've managed to power these to an acceptable volume is with a PAM8403 Class-D amp, making use of the balanced construction of the headset. This works ok, however I feel I shouldn't be needing a Class-D amp to run these. According to the specs these have 230 ohm earpieces. Any input on how to power these properly is welcome, surely a PAM8403 should be total overkill for this?
I have a power supply section providing both 9V and 5V through low dropout voltage regulators.
My more pressing issue is the microphone. The specs state the following:
MT7 MICROPHONE
Type: Dynamic differential microphone
Frequency range: 70–9000 Hz +/- 6 dB
Sensitivity as lip mike: 4 mV/220 Ω
Impedance: 230 Ω
Noise suppression: 12 dB at 1 kHz
It also has a balanced connection on the jack (I think? Mic+ and Mic-), however, there's no ground pin like there would be on an XLR plug. I've tried all sorts of things and the only way I've managed to get anything out of it is, weirdly, with the circuit for an Electret mic as the one used for normal headsets, with Mic- as ground. I feel I'm missing something obvious here, any input is welcome.
I apologise for not posting diagrams as I haven't got any to hand right now, but I'll try to update in a bit if the conversation requires it.
Thanks in advance!
First post here so please be gentle! I'm in the process of building an intercom system for my car, using the Peltor headset mentioned on the subject. As a newbie to all this it's proving harder than I thought.
The system should also be able to use normal smartphone type headsets. This part I have more or less sorted by using a TPA111A2 headphone amp to drive them and a simple NE5532 based electret preamp.
Back to the Peltors. These have a TP-120 TRRS connector, Tip + Ring1 are for the mic, and Ring2 + Sleeve are for the phones (L+ & R-, R+ & L- respectively as it only plays mono signals). The only way I've managed to power these to an acceptable volume is with a PAM8403 Class-D amp, making use of the balanced construction of the headset. This works ok, however I feel I shouldn't be needing a Class-D amp to run these. According to the specs these have 230 ohm earpieces. Any input on how to power these properly is welcome, surely a PAM8403 should be total overkill for this?
I have a power supply section providing both 9V and 5V through low dropout voltage regulators.
My more pressing issue is the microphone. The specs state the following:
MT7 MICROPHONE
Type: Dynamic differential microphone
Frequency range: 70–9000 Hz +/- 6 dB
Sensitivity as lip mike: 4 mV/220 Ω
Impedance: 230 Ω
Noise suppression: 12 dB at 1 kHz
It also has a balanced connection on the jack (I think? Mic+ and Mic-), however, there's no ground pin like there would be on an XLR plug. I've tried all sorts of things and the only way I've managed to get anything out of it is, weirdly, with the circuit for an Electret mic as the one used for normal headsets, with Mic- as ground. I feel I'm missing something obvious here, any input is welcome.
I apologise for not posting diagrams as I haven't got any to hand right now, but I'll try to update in a bit if the conversation requires it.
Thanks in advance!
You certainly picked non standard headphones for your project .
They are meant for the aviation industry usually ground staff and as well as a very limited frequency response for better clarity they have been passed by the FAA for use in hazardous situations.
As a result wiring is non standard , if you don't know earth contacts can cause sparking so safety characteristics are built in and the use of an attachable 2 way radio as a safeguard.
The electret mike is a charged unit using capacitance like a lesser electrostatic unit just think if that charge is earthed in an aviation environment and the contact is not zero ohms impedance .
Like you I have not come across a circuit diagram.
They are meant for the aviation industry usually ground staff and as well as a very limited frequency response for better clarity they have been passed by the FAA for use in hazardous situations.
As a result wiring is non standard , if you don't know earth contacts can cause sparking so safety characteristics are built in and the use of an attachable 2 way radio as a safeguard.
The electret mike is a charged unit using capacitance like a lesser electrostatic unit just think if that charge is earthed in an aviation environment and the contact is not zero ohms impedance .
Like you I have not come across a circuit diagram.