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Class-A Headphone Amplifier
Posted on Friday, April 11, 2008   •   Category: Headphone Amplifiers


Even if simple the circuit, plirej' all condition, regarding the distortion and the response of frequency. The resistance of entry is 250K and the load that can drive is between 100R and 2K. The circuit use negative coupling. His exit functions in Class A, having as active charge the BC308 and resistance 39R. The bias current is roughly 14 mA and total 15mA. The gain of unit is 25. The power supply, can be from 6V up to 24V DC. The frequency response with load 200R, it is 37ΗΖ - 470KΗZ (-1dΒ), the output voltage is 1.5V (11mW), the distortion 0.5%.


1 GHz Frequency Counter
Posted on Friday, April 11, 2008   •   Category: Counters / Frequency Meters


This simple counter is useful for frequency measurements of various wireless equipments, especially transmitters, receivers and signal generators in VHF/UHF band. Features * Display range: 0,0 to 999,9 MHz, resolution 0,1 MHz * Correct rounding, reduced blinking of last digit * Over-range indication * Fast measurement - short measuring period * High input sensitivity in VHF/UHF band * Switchable intermediate frequency offset for use with receiver.


1 min - 2 hours Timer with Buzzer and Optocoupler
Posted on Friday, April 11, 2008   •   Category: Timer Circuits


A small circuit that can find a lot applications of measurement time. She has the possibility us inform with sound signal from the BZ1. At the same time, exist the possibility drive a external circuit via the optocoupler IC2, after we connect the applicable circuit in contacts [ A ] and [ B ]. The circuit is based on IC1 (4060), which include in his inside, oscillator and a binary divider of 14 stage. The frequency operation of oscillator is determined by a circuit R-C that connected in pins 9,10,11 of IC1. We give supply in the circuit, with switch S1, is presented a pulse in 12 [ RESET ] via C1 and R3, null him counter, require the measurement of pulses to begin from the zero. Than the count get at in 14th digit then exit Q14 in the pin 3, acquire high logic level. This voltage drive the base the Q1-2, the transistors turn on, thus buzzer BZ1 sound, also the IC2 is ready to drive, via contacts [ A][B ], any suitable external circuit. The time delay is regulated with the potentiometer RV1, in time delay that begin from 1 minute up to 2 hours, proportionally with the combination of prices that they will have the RV1 and C2.


LM3875 Gainclone Amplifier
Posted on Friday, April 11, 2008   •   Category: Amplifiers


GainClones have VERY few components and this one is based on the National Semiconductor LM3875 IC. The PCBs and components are very simple and quick to make, only took about 20 mins to assemble both amps and rectifier board. DC offset was about 80mV on one channel and about 40mV on the other. I used the optional Ci capacitor in the national datasheet for the IC which reduced it to between 0-4mV: This is the capacitor I chose, its an Elna Starget (expensive). The case was MUCH more time consuming and difficult to make though. I bought all the aluminum from a scrap metal yard including the heatsink. I got my aluminum panels cut at a sheet metal shop as I cant make straight cuts with a hack saw.


1Hz to 1MHz Function Generator with XR-2206 IC
Posted on Thursday, April 10, 2008   •   Category: Frequency Wave Generators


Frequency Generator is an essential laboratory equipment for every electronic. It allows a variety of measurements and experiments. The module described here is based on high quality XR2206 IC and is extremely compact and inexpensive. Output frequency is from 1Hz to 1MHz. It provides sine, square and triangle waves around 1Hz to 1MHz, depending on the timing capacitors used. Over two Potentiometers the amplitude and frequency can be set. About trimmers can also have the purity of the sine signal and the offset of the output voltage can be changed.


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