Hey everyone!
I was tinkering with a circuit a couple of weeks ago and accidentally discovered a very useful circuit I personally have been needing and I've seen many other requests for it elsewhere upon researching it in the past.
My dilemma is that I'm not knowledgeable enough in electronics to know how to fine-tune/perfect the circuit and was hoping someone here might be interested in offering their expertise. I get the basic idea of how it works, but that's about it.
Technical Stuff
The voltage coming in from the "output" to power the microphone on an iPhone is approx. 2.7V. This is apparently what is powering this circuit and causing the amplification, if I understand how it works correctly.
The 4.7K resistor on the output is the minimum required impedance for the iPhone to recognize a microphone has been connected, otherwise it will default to the built-in mic and not accept the line input.
The 0.22uF was chosen for best treble/bass balance. Too low and it's all in the highs, too high of a capacitor value and the bass becomes distorted.
The 2N3904 seems to easily be replaceable with other NPN transistors. I've also tried the BC547 and it works just as well. I haven't carefully studied the technical specs to find the most ideal transistor and any suggestions here is appreciated.
The Input = The line-in varies. If using another iOS device, such as an iPad or iPhone, the input voltage is around 0.6 - 2mV. But from one of my computers, it varies from approx. 80-100mV, which is way too much and the volume must be turned really low or else it starts pulsating on and off (oscillating??) on the recording.
The Output = Using a 4-pole 3.5mm cable to RCA Video/stereo audio output, the red plug is the microphone input pin. It is obviously a mono input. Like I mentioned before, it requires 4.7K ohms of impedance before the iPhone switches over from the built-in mic to the line-in as if it were a headset with microphone.
It seems the 100K potentiometer is undersized or there needs to be more compensation via additional resistor(s).
The Goal
The fact it doesn't require any additional power makes it awesome and very compact. What would be ideal is for it to accommodate a variety of typical line-in devices such as iPod/mp3 players, other phones, computers, etc. and the potentiometer accommodate the variations of input voltages.
Thank you in advance for any help offered on this!
I was tinkering with a circuit a couple of weeks ago and accidentally discovered a very useful circuit I personally have been needing and I've seen many other requests for it elsewhere upon researching it in the past.
My dilemma is that I'm not knowledgeable enough in electronics to know how to fine-tune/perfect the circuit and was hoping someone here might be interested in offering their expertise. I get the basic idea of how it works, but that's about it.
Technical Stuff
The voltage coming in from the "output" to power the microphone on an iPhone is approx. 2.7V. This is apparently what is powering this circuit and causing the amplification, if I understand how it works correctly.
The 4.7K resistor on the output is the minimum required impedance for the iPhone to recognize a microphone has been connected, otherwise it will default to the built-in mic and not accept the line input.
The 0.22uF was chosen for best treble/bass balance. Too low and it's all in the highs, too high of a capacitor value and the bass becomes distorted.
The 2N3904 seems to easily be replaceable with other NPN transistors. I've also tried the BC547 and it works just as well. I haven't carefully studied the technical specs to find the most ideal transistor and any suggestions here is appreciated.
The Input = The line-in varies. If using another iOS device, such as an iPad or iPhone, the input voltage is around 0.6 - 2mV. But from one of my computers, it varies from approx. 80-100mV, which is way too much and the volume must be turned really low or else it starts pulsating on and off (oscillating??) on the recording.
The Output = Using a 4-pole 3.5mm cable to RCA Video/stereo audio output, the red plug is the microphone input pin. It is obviously a mono input. Like I mentioned before, it requires 4.7K ohms of impedance before the iPhone switches over from the built-in mic to the line-in as if it were a headset with microphone.
It seems the 100K potentiometer is undersized or there needs to be more compensation via additional resistor(s).
The Goal
The fact it doesn't require any additional power makes it awesome and very compact. What would be ideal is for it to accommodate a variety of typical line-in devices such as iPod/mp3 players, other phones, computers, etc. and the potentiometer accommodate the variations of input voltages.
Thank you in advance for any help offered on this!
An externally hosted image should be here but it was not working when we last tested it.
