Electronics circuits schematics

Dynamic mic preamplifier

admin — Thu, 24 Jul 2008 18:30:21 +0000

This mic preamp uses the low noise IC uA739. The circuit is an example of how a good preamplifier can be designed for dynamic microphones. The IC houses two identical integrated preamp circuits. The second preamp is used in identical manner for the second channel of the stereo microphone.
Diagram bellow shows the pin numbers (in brackers) for the second identical channel. All external parts are identical to those shown in the schematic.

The non-inverting input is biased at about 50% of the power supply. This bias voltage is set by the voltage divider circuit R1 and R4. The point between R1 and R4 is used commonly for both channels.
The unwanted HF signals coming from the microphone are filtered out by the RC-circuit composed of R3/C4. Frequency compensation is done by the R7/C6 circuit. The values of R7 and C6 were designed to avoid oscillation at the amplification level of 100. The input impedance is about 47K. This means that a normal dynamic microphone gets connected to a high impedance preamp which in turn produces good results. The output impedance is about several hundred ohms.
THe maximum peak-peak output voltage is about several volts lower than the supplied power. The frequency range is from 20Hz to 20KHz (-3dB). The upper cutoff frequency is 80KHz when the low-pass filter is removed from the circuit. The IC shown can be replaced with TBA231 or SN76131 without changind the external circuit.

Dynamic microphone preamp schematic

Cardiophone

admin — Wed, 23 Jul 2008 09:11:47 +0000

The human heartbeat can be made audible by using this cardiophone circuit. It is basically an audio circuit coupled to a probe made specially for the purpose of picking up electric signal from the human heart.
To get the best signal, place the probe’s electrodes to a point close to the heart. The preferred point is just below the left breast with negative electrode pointing the the left of the sternum.
After constructing the circuit, the output A must be calibrated to null through the potentiometer P1. This is important for the circuit to function properly. The signal coming from output A can then be connected to either a low-frequency amplifier or an oscilloscope.
The signal coming from output B is a square wave in sync with the heart rhythm. This signal can be used to trigger a final stage amplifier or other circuits. The heartbeat can be heard from the final amplifier’s speaker.

Cardiophone schematic

The special signal probe is shown in bellow figure and the simplest way to make this probe is to use a 1 cm x 10cm blank pcb board. Following the design, the non-shaded parts of the pcb board must be etched away. The un-etched copper plate must be covered with solder to protect it from corrosion and to facilitate good contact with the skin. Take note that two of the probe’s electrodes are marked negative and positive respectively. It is of utmost importance to use a shielded twisted pair wire for the cable connecting the probe with the cardiophone circuit.

Cardiophone probe

Cardiophone schematic layout

Samsung TFT NK15A, NK17A service manual

admin — Mon, 30 Jun 2008 16:27:18 +0000

Service manual for TFT-LCD TV/Monitor Samsung NK15A and NK17A.
Service manual contents:
1. Precautions
2. Product Specifications
3. Disassembly & Reassembly
4. Alignment & Adjustments
5. Troubleshooting
6. Exploded View & Parts List
7. Electrical Parts List
8. Block Diagram
9. Wiring Diagram
10. Schematic Diagrams
11. Panel Description
Download Samsung TFT NK15A, NK17A service manual guide

Service manual Sony FWD-42PV1A

admin — Mon, 30 Jun 2008 16:22:53 +0000

Service manual for Sony FWD-42PV1A FLAT WIDE DISPLAY, REMOTE COMMANDER RM-980, SPEAKER SYSTEM SS-SP42FW.
Sony FWD-42PV1A service manual contents:
- service overview
- service mode and adjustment
- troubleshooting
- spare parts
- block diagram
Download Sony FWD-42PV1A service manual guide

74F13 mini bug transmitter

admin — Sun, 29 Jun 2008 13:18:03 +0000

Take a look at this mini transmitter which can be used as a bug transmitter or for spy transmitter too. It uses a single IC 74F13, one coil, a capacitor, one trimmer, one resistor and ofcourse one electret mic. It is so easy to build and can give you a total coverage range of about 3 to 5 meters. You may want to use a small 100mW amplifier to give a little extend transmission range so you can spy from other location.
Please use only 74F13 because 74S13 and the other ones does not work in 88-108MHz range. As antenna you can use a copper wire (>=1mm diameter) and as power supply 4 x1.2 / min.1200mA acumulators which will work for at least 7 days. Use short terminal for components and a good pcb.

Mini bug FM transmitter circuit schematic

FM radio amplifier 25W

admin — Sun, 29 Jun 2008 13:06:58 +0000

A simple 25W fm radio amplifier used as a final stage for a 2.5W transmitter. I has a total gain of 10 dB and needs a 12V / 3A power supply. It is equiped with KT925W or BLY88, BLY89C. Use a very good headsink because this transistor get very hot
Coils values:
L1 = L3 = 4 turns / 1.5mm / 8mm / 10mm long
L2 = 4 turns / 1mm/6mm/10mm long
L4 = 20 turns / 0.8mm / on 100Ω resistor

25W FM radio amplifier circuit schematic

Amplification factor, power gain and dB

admin — Sun, 29 Jun 2008 10:29:02 +0000

To find the power gain ratio corresponding to a 3 dB change in level, use the formula:

The table showing the amplification factor if you know the power gain in dB

power gain dB	amplification factor
1	1.26
2	1.58
3	2
4	2.5
5	3.16
6	4
7	5
8	6.3
9	7.95
10	10
11	12.6
12	15.8
13	20
14	25
15	31.6
16	40
17	50
18	63
19	79.5
20	100

For example if we use BLY90 which has a power gain of 5 dB at 12.5V and 175MHz this results in a total amplification factor of 3.16 times. If we want to amplify 3W with BLY90 we’ll get almost 10W at the output.
There are different types of transistor, some have a huge power gain link 2N3866 which has a 20dB power gain at 28V 100MHz which results in an 100 times amplification factor. With only 10mW 2N3866 has a 1W output power.

FM antenna amplifier

admin — Sat, 28 Jun 2008 10:40:48 +0000

Use this fm antenna amplifier in areas where the signal reception of FM stations is too bad.
This circuit is just the right thing to do it. It is designed in such a way that the supply current powering it flows through coaxial cable. With this technique, an extra cable to power the fm antenna amplifier is unnecessary. The RF signal and the DC current supplying the amplifier use the cable simultaneously. The RF signal is however prevented by LC filters from flowing into the power supply. The amplifier works with either 50 ohm or 75 ohm antenna. It has a gain of 25 … 30 dB. MOSFETs are used to avoid the problem of crossmodulation or intermodulation. The circuit is divided into two parts. The first part is the active aplifier circuit which is normally installed very near the antenna. The second part is the power supply circuit which supplies current to the amplifier through the coax cable.
After the fm antenna amplifier circuit is constructed, the power supply should be connected to it. You must then test the DC voltage in the cable. This must be between 15.5 and 36.6 volts. Then test the voltage between T5 collector and ground while adjusting the supply voltage. It must move from 3 to 24 volts. The emitter of T2 should be approx. 11.4 volts. If the voltage at R4 is between 0.7 and 2 volts, then the MOSFET is functioning properly.

Important points to follow in constructing the circuit:
- The circuit must be constructed in a double sided PCB
- T1 must be shielded
- The source terminal of T1 must be soldered directly into the copper plate.
- C4 terminals must be as short as possible
- Coil terminals must be as short as possible
- The antenna must be conneted directly to L1
- T2 must be heatsinked

FM antenna amplifier circuit schematic

Power supply for the FM antenna amplifier

FM antenna amplifier active components and coils values

T1 = 3N225, 3SK85, 3SK87
T2 = 2SD781, 2SD1177, 2SD1684, MJE243, MJE244
T3 = 2SA970, 2SA1136, 2SA1137
T4, T5 = 2SC3622, 2SC3234, 2SC3248
L1 = 9 turns 0.7mm, tap at 1st turn from the ground
L2 = 6/3 turns (A&B) 0.5mm on Amidon T37-12
L3 = 9 turns 0.7mm, tap at 3rd turn from the ground

Sony KLV-S26A10/S32A10/S40A10 service manual

admin — Sat, 28 Jun 2008 10:12:59 +0000

Sony LCD TV KLV-S26A10/S32A10/S40A10 service manual contains:
SELF-DIAGNOSIS FUNCTION ……………….. 1-1
2. DISASSEMBLY …………………………………….. 2-1
2-1. KLV-S26A10/S32A10 ………………………………… 2-1
2-1-1. STAND ASSY REMOVAL …………………….. 2-1
2-1-2. REAR CABINET ASSY REMOVAL ………. 2-1
2-1-3. H1E BOARD REMOVAL ………………………. 2-2
2-1-4. VESA BRACKET ASSY REMOVAL ……… 2-2
2-1-5. SIDE BRACKET ASSY AND S1 TOP SHIELD REMOVAL …………. 2-3
2-1-6. G2 AND H2 BOARDS REMOVAL …………. 2-3
2-1-7. GE2 BOARD REMOVAL ………………………. 2-4
2-1-8. A2G BOARD REMOVAL ………………………. 2-4
2-1-9. BG BOARD REMOVAL ………………………… 2-5
2-1-10. H3 BOARD AND SPEAKER REMOVAL …. 2-5
2-1-11. LCD PANEL REMOVAL ……………………….. 2-6
2-2. KLV-S40A10 …………………………………………….. 2-7
2-2-1. STAND ASSY REMOVAL …………………….. 2-7
2-2-2. REAR CABINET ASSY REMOVAL ………. 2-7
2-2-3. H1E BOARD REMOVAL ………………………. 2-8
2-2-4. VESA BRACKET ASSY REMOVAL ……… 2-8
2-2-5. SIDE BRACKET ASSY AND S1 TOP SHIELD REMOVAL …………. 2-9
2-2-6. H2 BOARD REMOVAL …………………………. 2-9
2-2-7. G3 BOARD REMOVAL …………………………. 2-10
2-2-8. A2G BOARD AND GE2 BOARD REMOVAL .. 2-10
2-2-9. BG BOARD REMOVAL ………………………… 2-11
2-2-10. H3 BOARD AND SPEAKER REMOVAL .. 2-11
2-2-11. LCD PANEL REMOVAL ……………………….. 2-12
3.Sony KLV-S26A10/S32A10/S40A10 ADJUSTMENTS ……………………………………. 3-1
3-1. Signal Adjustment …………………………………………. 3-1
3-1-1. PAL auto adjustment (CVBS) ……………………. 3-1
3-1-2. NTSC auto adjustment (CVBS) ………………….. 3-1
3-2. White Balance Adjustment ……………………………… 3-1
3-2-1. White Balance adjustment (H/L) ………………… 3-1
3-2-2. White Balance adjustment (C/O) ………………… 3-2
3-2-3. SECAM White Balance adjustment (H/L) …… 3-2
3-2-4. SECAM White Balance adjustment (C/O) …… 3-3
3-3. TEST TEST MODE ………………………………………. 3-3
4.Sony KLV-S26A10/S32A10/S40A10 TROUBLESHOOTING……………………………. 4-1
5.Sony KLV-S26A10/S32A10/S40A10 DIAGRAMS …………………………………………… 5-1
Schematic Diagrams of A2G BOARD
Schematic Diagram of G2 BOARD
Schematic Diagrams of G3 BOARD
Schematic Diagram of GE2 BOARD
Schematic Diagram of H1E BOARD
Schematic Diagram of H2 BOARD
Schematic Diagram of H3 BOARD
Sony KLV-S26A10/S32A10/S40A10 LCD TV EXPLODED VIEWS ……………………………….. 6-1
6-1. KLV-S26A10/S32A10 ………………………………… 6-2
6-1-1. REAR CABINET ASSY AND STAND ASSY .. 6-2
6-1-2. CHASSIS-1 ……………………………………………. 6-3
6-1-3. CHASSIS-2 ……………………………………………. 6-4
6-1-4. CHASSIS-3 ……………………………………………. 6-5
6-1-5. CHASSIS-4 ……………………………………………. 6-6
6-1-6. LCD PANEL ………………………………………….. 6-7
6-2. KLV-S40A10 …………………………………………….. 6-8
6-2-1. REAR CABINET ASSY AND STAND ASSY .. 6-8
6-2-2. CHASSIS-1 ……………………………………………. 6-9
6-2-3. CHASSIS-2 ……………………………………………. 6-10
6-2-4. CHASSIS-3 ……………………………………………. 6-11
6-2-5. CHASSIS-4 ……………………………………………. 6-12
6-2-6. LCD PANEL ………………………………………….. 6-13
6-3. PACKING MATERIALS (KLV-S26A10) ……. 6-14
6-4. PACKING MATERIALS (KLV-S32A10) ……. 6-15
6-5. PACKING MATERIALS (KLV-S40A10) ……. 6-16
7. ELECTRICAL PARTS LIST ……………………. 7-1
Download sony lcd tv klv-s26a10/s32a10/s40a10 service manual

Automatic volume control

admin — Fri, 27 Jun 2008 09:50:33 +0000

The function of this automatic volume control circuit is to amplify signals without distorting its dynamic compression. The amplitude differences in the signal are levelled off and the disturbing effect vanish. With this tehnique, overcompensation in the volume is avoided. The circuit is used to automatically control the volume levels of cassette recorders, audio tape recorders, amplifiers or radio devices.
The AVC circuit works this way: the FET (t1) is used as a variable resistor. The resistance between the drain and source of T1 can be between 150Ω and infinite. It is parallel to R2 and togheter with R3 controls the gain of OP amp A1 (around 20 dB). The following OP amp A2 is wired as an amplifier with P1 as its gain control. The negative part of the output signal coming from A2 is rectified and fed to the gate of T1. Small variations on the signal amplitude does not influence the amplification since the FET has a short delay caused by R6. The opposite effect is also slow because of the discharge time of C1. Both effects result to a smooth regulation of the signal amplitude, making this automatic volume control circuit so effective.
The signal voltage at the gate of T1 must be as low as possible to influence the drain-source resistance. To achieve this, the voltage divider R1, R4 is set at the input line to attenuate the signal by 40 dB. This tehnique enables signals up to 1 Veff to be processed without a problem and with distorsions level below 0.5%. The signal-noise ratio is over 70dB by an input voltage of 1Veff. The losses at the attenuator is compensated by the amplification through Ai and IC2.
The high pass filter made of C2, R7 prevents the bass signals from influencing the regulation. With proper dimensioning of these components , the cutoff frequency of this filter can be adapted to individual needs. Signals below the threshold set by P1 are amplified by around 18dB.
The automatic volume control circuit need a symmetrical supply of +/- 15 volts and consumes around 7mA.

Automatic volume control circuit schematic

AVC printed circuit layout

Automatic volume control parts placement layout

AVC supply connections