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The device for anesthesia

Musical "anesthesia"

Ing . P. Wainboim, G. Mironenko, Leningrad

While examining the old archives, I came across this article and decided to share it. Once upon a time, being a student at the Gorky Radio Technical School, this device was the topic of a graduation project for my fellow student and fellow lab. The whole process of assembly and testing of the device passed before my eyes. The design of the assembled instrument was somewhat different - a high-quality reel   record player   (it seems "Jupiter 001-stereo") and slightly changed the circuitry . The initial skepticism towards this device was replaced by confidence in its effectiveness after the first tests in the dentist's office. In addition, we used this device simply to rest in breaks between work. Interested persons can make such a device, based on the principle stated in the article below. And, using modern means of sound reproduction, for example CD-player, and modern circuitry , it is possible to create a compact device. So, the idea is - go!

Nikolay Bolshakov.

The device offered to the attention of readers is intended for anesthesia during the treatment of teeth and prosthetics. Everyone knows what unpleasant omissions arise when the tooth is treated with a drill. It is understandable therefore the interest of specialists in the problem of anesthesia in the treatment of teeth. At one time, many methods were proposed, but none of them was sufficiently effective. The most promising was the so-called method of sound analgesia. It is that during the treatment the patient listens to the music program and white noise (a mixture of all components of the sound spectrum of frequencies) applied to the headphones. Music beneficially affects the nervous system of the patient, and white noise extinguishes the focus of excitation in the cerebral cortex, caused by pain.

Device   for    anesthesia    (sound    analginizer )    was    designed    Leningrad    engineer P. Weinboim in collaboration with the doctor of the Military Medical Academy. S. M. Kirova G. Mironenko. The creation of the device was greatly assisted by the techniques of V. Kuznetsov and F. Gulyanitius .

During the two-year operation in the dental department of the polyclinic of the Military Medical Academy, the sound analgesizer invariably received good patient feedback. The device was exhibited at the 17th Leningrad exhibition of creativity of radio amateurs-designers DOSAAF and was awarded a diploma of the I degree.

A block diagram of the sound analyzer is shown in Fig. 1. The device consists of an LF amplification unit, a mixer unit (patient panel), a power supply unit and a tape drive with an endless loop of magnetic tape. Its purpose is to simultaneously play the music program and white noise recorded on the four tracks of the tape. The device uses low - impedance two - channel reproducing heads with a working gap of 3 microns , a magnetic tape of type 6, a belt speed of 9.53 cm / s.

Correction of the frequency response in the cascade of the preamplifier LF allows to achieve high-quality reproduction in the frequency range up to 10 kHz .

In Fig. 2 is a schematic diagram of a sound analyzer . All four signals are removed by magnetic heads from the tracks of the magnetic tape, the voltage of the signal goes to the corresponding preamplifier LF made on transistors T1-T3. Two preamp low-pass amplifiers amplify the music channel signals ( Am and Bm ), and the other two - noise channel signals ( Ash and Bash ). At the input of the low end amplifier using passive mixers (R10, R11, R23 and R24), music and noise are mixed in the required ratios. After mixing and amplifying the signal voltage with two low-end amplifiers (T4-T9), the signals Am + Am are fed to one of the headphones, and Bm + Bm to the other, resulting in a binary effect. If necessary, the patient can adjust separately the amount of music and noise from zero to maximum.


Three - stage preamplifier LF is made on transistors T1-T3 (P13B). The amplifier is covered by frequency-dependent negative feedback of 19 dB depth. The first cascade of the amplifier is made according to the scheme with a common emitter. The playback head is connected to the input of the amplifier through the capacitor C 1 . The transistor used in the first stage should have a minimum noise level. To match the first stage with the next one, an emitter follower galvanically coupled to the first stage is used. The third cascade is similar to the first one. The negative feedback voltage is supplied from the collector circuit of the last transistor (T3) to the emitter circuit of the first through the elements C4R4R6. The output stage is loaded onto the level controller, which is located in the remote mixer block.

The mixer unit, designed as a separate panel, is a rheostat divider consisting of two coupled potentiometers (R10 and R24) and decoupling resistors R11, R23. Potentiometers act as regulators of the level of music and noise. Isolating resistors are necessary to eliminate the mutual influence of the outputs of the preamplifiers of LF. Resistors of these resistors are selected experimentally.

The terminating amplifier raises the signal level to the required level for normal playback in headphones. This amplifier should have a small coefficient of nonlinear distortion, high input impedance, low voltage gain and additional correction of the frequency response in the low frequency region (approximately 4 dB per octave).

The final amplifier is assembled on six transistors (T4-T9), five of which are of the type p-n-p , and the sixth (T9) is of the type n- p-n (P10).

The first and third stages, performed on transistors T 4 and T 6 according to the common emitter scheme, amplify the signal voltage. The second and fourth stages on transistors T5 and T7 (according to the scheme of the emitter follower) serve to match the output resistances of the previous stages with the input resistances of the subsequent ones.

The output stage is a two-stroke power amplifier, assembled in a common collector circuit with transistors of different conductivity. This makes it possible to dispense with a phase-inverted cascade. The amplifier is covered by deep feedback (26 dB ), which sharply reduces the coefficient of nonlinear distortion. The feedback voltage depends on the frequency ( frequency dependent feedback), so that an additional correction of the frequency response of the reproduction channel in the low-frequency region is achieved. In addition, the input resistance of the final amplifier covered by feedback is increased. The amplifier is not critical to the load.

The power supply of the device contains a voltage regulator on the transistors T10, T11. The reference voltage is removed from a silicon zener diode of type D811. The rectifier is assembled on a bridge circuit using four D7A germanium diodes. The whole device is powered by AC power through a power transformer.

The kinematic scheme of the tape drive mechanism is shown in Fig. 3. The use of an endless loop of magnetic tape placed in a special cassette made it possible to simplify the tape drive mechanism and use a low-power engine such as EDG-1M.

Cassette apparatus is a plastic box with a roll of tape length 230 m , which is wound on a disk base freely rotating on the axis of the cassette. Working diameter of the drive shaft 5 mm . Due to the use of an endless belt loop, rewinding is not necessary, and the machine is always ready for action. The tape drive mechanism is operated by a toggle switch that turns on the motor power and presses the drive roller to the shaft. Two stereo heads are located directly under the cassette body.

For reliable contact of the magnetic tape with the heads, a special felt clip is used, which is removed at the moment of switching on the device.

Structurally, the whole apparatus is made in the form of a separate block (Fig. 4). Machine weight 5 kg . Its dimensions are 230X150X105 mm. The top cover is removable.

On the upper panel of the device, a cassette with a device for mounting and pressing the magnetic tape to the shaft, two stereo heads and an on / off switch (Fig. 5) are reinforced. The thermal heads are closed with a safety cover.

Under the panel is a board made of B-95 alloy 6 mm . It is strengthened by a tape drive mechanism, which includes an EDG-1M electric motor, a flywheel with a driving   shaft,   thrust   management   and   clamp (Figure 6). On the same board, the entire electronic part, consisting of a four-channel playback amplifier, power supply unit, power transformer and connecting pads, is reinforced.

Preliminary amplifiers of reproduction are executed in the form of the separate block. It is mounted on a box-shaped steel chassis. The chassis dimensions are 160X80X40 mm. All four amplifiers are assembled on textolite boards and separated from each other by screens (Figure 5).

The final amplifiers are assembled on two PCBs and are located on the other side of the installation of the preamplifiers. The control panel is made in the form of a separate unit. The structure of this unit includes two dual potentiometers, playing the role of level controllers, and output pads for connecting the headphones of the doctor and the patient.

Fig. 3 . Kinematic scheme of the tape drive mechanism: 1. Shaped disk,   2. Roll   films,   3. Sleeve   disk, 4. Base, 5. Pressure roller, 6. Guide column, 7. Drive shaft, 8. Magnetic reproducing stereo head ,    9. Clamping    strap,    10. The felt    overlay,    11. Loop    magnetic    tape.     12. Flywheel. 13. The lavsan belt, 14. The axis of the engine, 15. The thrust of the flywheel, 16. The electric motor.













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