How to turn a digital voice recorder into a spy gizmo?

As a result of many years of activity, the stock of parts and electronic components of the home maker is constantly being replenished. It goes without saying: fully serviceable parts of a defective multifunctional device can work separately in other designs. This is the case, for example, when it is unprofitable to repair an electronic device.

Another reason for “stocking up” is the almost inevitable upgrade of household or computer equipment. To this end, old electronic devices are deposited in the hobbyist’s pantry. Do not throw away such a device just because it was made in the last century. And so, having disassembled their “bins”, connecting the old with the new, you can get that still a hybrid from electronics.

K-12C hearing aid: Just add a voice recorder

Some of these illiquid inventories are hearing aids. These devices amplify the sound many times and are equipped with highly sensitive microphones such as Sosna-3M, MEK3-221 and similar , so they are recommended to people with impaired hearing. Consider one of these K-12C hearing aids, shown in Photo 1.

Photo 1. Hearing aid K-12S

The hearing aid is equipped with a clothes clip, a power switch, a volume control, a built-in microphone, and an earphone jack at least 250 ohms . The connector is quite unusual.

The evident “minus” of the device is that there is no jack for the external microphone. However, this “minus” can easily be turned into a “plus” if you imagine that the hearing aid itself can become a remote microphone for any audio equipment, such as voice recorders, amplifiers and even radio receivers.

AA type cell with a rated voltage of 1.5 V is used as a self-contained power source. The current consumption of the device is very low, so the operating time at maximum volume in the earpiece maximum volume is not always needed is more than 300 hours of uninterrupted operation.

Using a high sensitivity microphone and high gain hearing aid paired with a digital recorder, you can get a result that surpasses modern portable audio systems multiple amplification.

How to choose a digital voice recorder

Today’s popular compact digital voice recorders with high-sensitivity microphones, self-powered, simple controls and are adapted to work with a computer. The duration of the sound recording of some models is up to 20-30 days. Audio and video materials are accepted as evidence in court, help all interested people at lectures, seminars, exhibitions and in many similar cases.

Most people use digital voice recorder from time to time, so I do not recommend to buy a very expensive “toy” – the process of “electronic” aging devices is fast, every year there are more advanced systems.

I would like to draw your attention to compact digital voice recorder Sony BX112M 2GB photo 2 , which is an improved line of popular digital voice recorders Sony ISD-P520, which I have faithfully served for over 5 years photo 3 .

Photo 2 and 3. Sony BX112M 2GB Digital Voice Recorders and Sony ISD-P520

Digital voice recorder Sony BX112M 2GB – multifunction device with built-in 2 GB electronic memory provides a maximum recording time of 534 hours. Playback of MP3-files mono is through the built-in speaker, the maximum power of 300 mW.

Recording – with digital microphone sensitivity control.

The recorder is equipped with an LCD display and has the following service functions

• voice activation
• Different quality recording: for example, the maximum recording time of 25 hours 00 minutes high quality or 534 hours 00 minutes low quality
• accordingly, the organization of the internal built in memory is such that the maximum number of folders for messages is 5, and the message files themselves 495.
• there is a microphone input and headphone output
• battery power indicator
• Remaining recording time indicator
• Power – 2 AAA batteries
• 2 batteries
• clock, alarm clock, message scanning.

How to record so no one can see but everything can be heard?

If you put the old cassette recorder in your inside pocket, the sensitivity of the built-in microphone decreases, which makes sense – clothing absorbs the sound vibrations of your voice. In addition, the built-in microphone picks up the noise of the LPM motor.

Electronic compact voice recorders don’t have this problem, but there is another one – the built-in electret microphone is so sensitive that any murmur in the pocket for example, when you change your pose will be amplified many times and then played back almost like the sound of a hammer on an anvil.

Electronic voice recorders with built-in memory card are less sensitive to weak signals, moreover their ageing period is about 1-1,5 years. In a year a dictophone of the same model will be difficult to buy.

So, for covert recording on a dictaphone, a highly sensitive remote electret microphone amplified with a hearing aid would be the best choice.

Choice of remote microphone

Among the electret microphones have good electrical characteristics at a low cost 300-400 rbl. in the author’s experiments showed Minor-06 microphone. This clip-on clip-on microphone is designed to record faintly audible sounds from distant sources. It works well with any recorder, including voice control. The microphone is equipped with a switch on the cord. In the position where the red dot on the switch body is visible, the microphone is active.

Improving the quality of information playback with built-in speaker of Sony BX112M 2GB voice recorder.

Built into the recorder regular high-frequency speaker is not the best option for such a device. So it is desirable to install a better dynamic head instead of the regular one.

Excellent results in terms of frequency bandwidth and sound volume can be achieved with dynamic heads like YD40-02 or YD80-04 both with 4 ohms resistance and 0.4 W and 0.8 W power respectively . Experimenting with them confirmed their excellent quality and excellent compatibility with the recorder.

However, by improving something, other features are more often than not compromised. Therefore, “finalizing” in your own way voice recorder, it is necessary to define clearly – what is more important: a better recording of weak sounds when concealed carry the recorder or the ability to quickly convert the recording into a digital form for example, using a personal computer .

Wiring and setup features

So, you can additionally increase the sound by combining the sound recorder and the hearing aid. You will need a shielded audio cable, a headphone jack and a WS-12 connector for connecting the remote microphone to the recorder. As a rule, an additional microphone is not included with the recorder, and it is purchased separately.

Even better, if you already have a ready-made remote microphone, such as Minor-06, equipped with a clothes clip, a switch on the wire and a WS-12 jack. From this microphone, you can take everything except the microphone itself: a standard jack connect to the input of the recorder – to the socket “remote microphone” , wire and switch. At the other end of the wire, connect the hearing aid connector photo 5 .

Photo 5. Connector for a hearing aid

There, actually, and all rework – the old hearing aid plus the new voice recorder and the spy thingy has turned out, not worse, than agent 007’s.