Showing posts with label low. Show all posts
Showing posts with label low. Show all posts
Monday, January 26, 2015
Low Cost Playback Amplifier For Cassette Deck
For some time now, there have been a number of tape cassette decks available at low prices from mail order businesses and electronics retailers. Such decks do not contain any electronics, of course. It is not easy to build a recording amplifier and the fairly complex magnetic biasing circuits, but a playback amplifier is not too difficult as the present one shows.
The stereo circuits in the diagram, in conjunction with a suitable deck, form a good-quality cassette player. The distortion and frequency range (up to 23 kHz) are up to good standards. Moreover, the circuit can be built on a small board for incorporation with the deck in a suitable enclosure. Both terminals of coupling capacitor C1 are at ground potential when the amplifier is switched on.
The stereo circuits in the diagram, in conjunction with a suitable deck, form a good-quality cassette player. The distortion and frequency range (up to 23 kHz) are up to good standards. Moreover, the circuit can be built on a small board for incorporation with the deck in a suitable enclosure. Both terminals of coupling capacitor C1 are at ground potential when the amplifier is switched on.
Cassette Deck Playback Amplifier Circuit Diagram:
Because of the symmetrical ±12 V supply lines, the capacitor will not be charged. If a single supply is used, the initial surge when the capacitor is being charged causes a loud click in the loudspeaker and, worse, magnetizes the tape. The playback head provides an audio signal at a level of 200–500 mV. The two amplifiers raise this to line level, not linearly, but in accordance with the RIAA equalization characteristic for tape recorders. Broadly speaking, this characteristic divides the frequency range into three bands:
- Up to 50 Hz, corresponding to a time constant of 3.18 ms, the signal is highly and linearly amplified.
- Between 50 Hz and 1.326 kHz, corresponding to a time constant of 120 µs, for normal tape, or 2.274 kHz, corresponding to a time constant of 70 µs, for chromium dioxide tape, the signal is amplified at a steadily decreasing rate.
- Above 1.326 kHz or 2.274 kHz, as the case may be, the signal is slightly and linearly amplified. This characteristic is determined entirely by A1 (A1’). To make the amplifier suitable for use with chromium dioxide tape, add a double-pole switch (for stereo) to connect a 2.2 kΩ resistor in parallel with R3 (R3’). The output of A1 (A1’) is applied to a passive high-pass rumble filter, C3-R5 (C3’-R5’) with a very low cut-off frequency of 7 Hz. The components of this filter have exactly the same value as the input filter, C1-R1 (C1’-R1’). The second stage, A2 (A2’) amplifies the signal ´100, that is, to line level (1V r.m.s.).
Sunday, November 2, 2014
Low Power LED Flasher
It doesnt get much simpler than this circuit. Four components counting the battery!
How can an LED be illuminated by a 1.5V circuit, when the forward voltage of an LED is about 2V? The LM3909 uses the 100uF capacitor as a charge reservoir, building up a voltage of about 2V before discharging the cap through the LED.
This circuit is used in emergency flashlights on airplanes and in other public places. Though you may not have known it till now, the LM3909 is everywhere!
Low Power LED Flasher
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How can an LED be illuminated by a 1.5V circuit, when the forward voltage of an LED is about 2V? The LM3909 uses the 100uF capacitor as a charge reservoir, building up a voltage of about 2V before discharging the cap through the LED.
This circuit is used in emergency flashlights on airplanes and in other public places. Though you may not have known it till now, the LM3909 is everywhere!
Low Power LED Flasher
Tuesday, September 2, 2014
Build a Low Forward Drop Rectifier Wiring diagram Schematic
A TMOS power FET, Ql, and an LM393 comparator provide a high-efficiency rectifier schema. When V,. exceeds V,, Ul`s output becomes high and Ql conducts. Conversely, when VB exceeds V,., the comparator output becomes low and Ql does not conduct.
The forward drop is determined by Ql`s on resistance and current I. The MTH40N05 has an on resistance of 0. 028 !l; for I = 10 A, the forward drop is less than 0.3 V. Typically, the best Schottky diodes do not even begin conducting below a few hundred mV.
Low Forward Drop Rectifier Circuit Diagram
Low Forward Drop Rectifier Circuit Diagram
Friday, August 22, 2014
Power Supply 1 2 12V 1A with low voltage LED Indicator
This power supply can provide output voltage 1.2V - 12 with maximal output current is 1A, low voltage LED indicator added in this schematic diagram. The indicator part includes three diodes and one LED. For example you are charging a battery, you can observe the charge status at that moment. Another advantage of this schema, when the drawn current exceeds 1A (practically 0.85A), the current protector in LM317 intervenes and LED indicator warns you about the very low output voltage.
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