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Headphone Amplifier - An amplifier to drive low to medium impedance headphones built using discrete components __ Designed by Andy Collison
Heart of LEDs - Here is a fun project that you can give to that "someone special". How about Mother's Day or did you forget St Valentine's Day?. __ Designed by © Grantronics Pty Ltd
Heating System Thermostat - This circuit is intended to control a heating system or central heating plan, keeping constant indoor temperature in spite of wide range changes in the outdoor one. Two sensors are needed: one placed outdoors, in order to sense the external temperature; the other placed on the water-pipe returning from heating system circuit, short before its input to the boiler. __ Contact: Flavio Dellepiane, fladello @ tin.it
HF 5-band MOSFET power Amplifier Delivering 30 watts - Ham RadioAF AmplifiersThis project uses a widely available IRF510 MOSFET. This N-Channel enhancement mode silicon gate power field effect transistor is an advanced power MOSFET designed, tested, and guaranteed to withstand a specified level of energy in the breakdown avalanche mode of operation __ Designed by Guy Roels ON6MU
HI FI Headphone Amplifier - The intention is to permanently insert the headphone amp between pre and power amps, although it can be used as a stand-alone item. The input relay is operated by auxiliary contacts on the headphone sockets through a transistor driver (with a small delay) so as to mute the power amp input when listening on headphones. __ Designed by Richard Crowley
Hi-Fi Headphone Amp - The intention is to permanently insert the headphone amp between pre and power amps, although it can be used as a stand-alone item. The input relay is operated by auxiliary contacts on the headphone sockets through a transistor driver (with a small delay) so as to mute the power amp input when listening on headphones __ Designed by Rod Elliott ESP
Hi-Fi Headphone Amplifier - The intention is to permanently insert the headphone amp between pre and power amps, although it can be used as a stand-alone item. The input relay is operated by auxiliary contacts on the headphone sockets through a transistor driver (with a small delay) so as to mute the power amp input when listening on headphones. __ Designed by Richard Crowley
High Current Regulated Power Supply - The high current regulator below uses an additional winding or a separate transformer to supply power for the LM317 regulator so that the pass transistors can operate closer to saturation and improve efficiency. For good efficiency the voltage at the collectors of the two parallel 2N3055 pass transistors should be close to the output voltage. The LM317 requires a couple extra volts on the input side, plus the emitter/base drop of the 3055s, plus whatever is lost across the (0.1ohm) equalizing resistors (1volt at 10 amps) , so a separate transformer and rectifier/filter circuit is used that is a few volts higher than the output voltage __ Designed by Bill Bowden
Interfacing 5 Volt CMOS
to 12 Volt loads - The circuit above is designed to be used with the bi-directional lamp sequencer shown above on this same page. Two additional transistors are used to increase the current from the 74HCT138 decoder to control 12 volt 25 watt lamps. A 6.8 volt/1 watt zener diode is used in series with the ground connection of all the CMOS
ICs (74HC14, CD4516 and 74HC138s) so that the total voltage across the CMOS
devices will be about 5.2 volts and the outputs will move from +12 to about +7 when selected. The 2N2905/PNP transistor stage is connected as an emitter follower which provides a high impedance to the __ Designed by Bill Bowden
Lapel microphone adaptor for PA systems - Simple adaptor features a balanceed output and lets you use electret lapel and headset microphones with PA systems. __ SiliconChip
LF071 Mic Amplifier - A high quality microphone preamplifier using a single power supply, suitable for dynamic or electret microphones. The op-amp used can be any low noise, high performance type, e. g. NE5534, TL071, OPA 371 etc __ Designed by Andy Collison
Little Guitar Amp - I built this little guitar amp for my brother, Rich, a while back. Originally it was sort of a Fender "Champ" copy with a 12AX7 front end. I recently converted it to use a single EF86 pentode, instead. I like it much better this way. The amp chassis fits into a small maple open-back box with a single 10" speaker. Rich built the box __ Designed by Bob Danielak
LM317 Regulator with Pass Transistor The LM317T output current can be increased by using an additional power transistor to share a portion of the total current. The amount of current sharing is established with a resistor placed in series with the 317 input and a resistor placed in series with the emitter of the pass transistor. In the figure below, the pass transistor will start conducting when the LM317 current reaches about 1 amp, due to the voltage drop across the 0.7 ohm resistor __ Designed by Bill Bowden
LM386 Audio Amplifier - Here is a simple audio amplifier circuit built around 8-pin integrated circuit LM386. The author’s prototype is shown in Fig.1. Circuit and working Circuit diagram of the LM386 audio amplifier is shown __ Electronics Projects for You
Low Power Audio Amp Experiments - The object of this experiment is to assemble and test a low-power audio amplifier that might be used to drive headphones. Because an op amp is current limited to less than 25 mA, it cannot be used to directly drive a low impedance load. A solution to this problem is to add current boosters between the op-amp output and the load as shown in Figure 1
Low Power Audio Amplifier Based on LM386 - Another super-simple circuit. You could use this circuit to drive a low power speaker from a sound effects module or a noise generator. Or you could build your own amplified speakers for use with your computer. __ Designed by Bill's Electronics Reference Library
Low power audio Amplifier using BC109C along with BD679 & BD680 Darlington pairs - As can be seen from the circuit diagram we are really using five transistors as the BD679 and BD680 are "Darlington" pairs of transistors. The led must be a green led for correct operation. (The voltage across a green led is higher than the voltage across a red led.) When using a 12v supply the voltage at T1 collector should be (about) 5v and at T2 base (about) 7v. This amplifier will be unstable (it will oscillate) without the 4k7 variable resistor connected to the input. __ Designed by © David Hoult
Low Power Single-Ended 6SN7 Amp - I built this little amp for my computer at work. It sounds pretty darn good thru some old speakers from an Emerson tube console. At <1/2 Watt it is STILL too loud for my office. __ Designed by Bob Danielak
Low Power Single-Ended 6SN7 Amp power supply - This is the power supply for the 6SN7 Amp __ Designed by Bob Danielak
Low-Power Audio Amplifier based on LM386 - Another super-simple circuit. You could use this circuit to drive a low power speaker from a sound effects module or a noise generator. Or you could build your own amplified speakers for use with your computer. __ Designed by Bill's Electronics Reference Library
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