Almost Silent Sound On a Spy Pen

Did it work before you started changing things?

No, it was like that when I got it. I thought it might have been an incorrectly connected microphone but it seems to be something else.

Sounds like you need more gain in the mic circuit.

Did you try it before you bought it?

It was bought online. I have looked at the capacitors for the microphone that are used for noise reduction and removing them made no difference. I can not see a microphone circuit anywhere.

Here's what you need, something like this...

http://www.supercircuits.com/Microphones/PA3WP

I have a few suggestions, two comments and a couple of questions.

Suggestions:

• Since this microphone is not designed for this circuit, you might be overloading the microphones drive capability. Raising the input impedance of the amplifier from the pen may help your problem.
• You can increase the gain of the amplifier. If this is not possible, a preamplifier to boost your new microphone maybe necessary.

Comments:

• Your choice of terms is contradicting and confusing. Sound cannot be very clear and silent. I suspect that this is due to English not being your native language. This may also be due to being unfamiliar with audio electronics and terminology. So all of us should be tolerant of each other in our mutual attempts to communicate across one language barrier or another.
• If you can, it will be helpful if you could paste a schematic drawing of at least the critical part of the circuit you wish to discuss. This will greatly reduce confusion.

Questions:

• What type of microphone are you using instead of a condenser microphone?
• Who are you trying to bug with a spy pen?

I am trying to put it on a kite and was wanting sound. I am meaning that the the pen can pick up the sound very clearly if you put it through a high gain amplifier. In this case, I used music at full volume from the headphone socket. I have tried poking around the circuit board with a microphone but I can not come up with anything.

I was only using condenser microphones with it. I tried a dynamic microphone but that is just as quiet.

An audio recording spy pen is designed to record the sounds heard clearly within earshot of a normal person holding or wearing this pen. Likely the microphone will pickup sounds in an omnidirectional pattern so that the pen/microphone does not have to be pointed at a subject. Often these surreptitious recording devices suffer from the interference of wind noises. A kite relies on wind to lift itself and possibly a payload a string limited distance above the earth. You are taking a microphone package designed to operate in close proximity to those who are speaking and taking it away from close proximity. I would expect that the sound recorded by this pen and kite combination would be hard to hear.

Microphones designed to pick up distant sounds are much more expensive devices like a parabolic microphone for very long distances and a shotgun microphone for moderate distances. Both of these microphones are very directional devices so they must be aimed to pick up their distant sounds. Also both devices will likely disrupt the airflow around your kite, so even though they will have the range you desire they will not be effectively lifted by a kite.

So an omnidirectional microphone is what you likely need with this spy kite but the range of the spy pen microphone must be boosted. The only plausible method I see is a preamplifier placed between microphone and recording device. This increased range will create complications of trying to isolate one conversation in the sea of many sounds most of the time, but this can be done. The size and weight limitations you have for being used in a kite imply to me that this should be a very small light weight custom amplifier.

I would use for a final package design surface mounted components if not hybrid die encapsulation circuitry. I would first measure the input and output impedances of the recorder found in the pen and the microphone suitable for your kite. I would then estimate the signal levels produced by that microphone on the kite at a suitable altitude above some talkers to determine how much added gain is needed. Then I'd design and build a bulky discrete component prototype amplifier with the anticipated amount of added gain. Only after successful testing of a prototype design would I then try to make an amplifier small and light weight enough for use on a kite.

Did you try calling the manufacturer? Or maybe it's just plain broke and won't work no matter what you change.

It surely sounds like what you need is a preamp. A tiny one, of course.

Your external mic cell may require a bias voltage to work.

Try faffing around with some batteries. That's all I can suggest sight unseen.

Step one would be to get the extant mic's gain up where you want it.

Buying online...oh dear.

What are you hoping to hear up there anyway?

check the law. owning one is legal. recording some one with it is a felony.

The original mic is most likely an "electret microphone", which requires a small bias voltage which the original circuit would provide. Any other type mic, dynamic or condenser will not work! Check the battery in the pen to assure it is at full voltage and making good contact in its holder. Cheaper, original, batteries will self discharge maybe even before the pen was shipped to you. Use a lithium battery as replacement.

...and when it is working you might well need a "wind cap" or something to keep the wind from making too much noise in the mic directly while you're trying to hear the sound of the wind from the kite's movements. Good luck and success.

Remember in some places (MD for instance) it's illegal to record someone without permission.

I have a small listening device that amplifies sound and sends it to an earplug. The microphone quit working after a year or so and I took the microphone out of an old cell phone and soldered it onto the wires that went to the original mike. It worked very well but the new mike would not fit where the old one was so I had to tape it to the outside of the device. It still works good and I only use the device for listening, not for recording. I am not spying, at my age there are a lot of things I just cannot hear without some help.