741 | Electronic Project Circuits

Posts Tagged ‘741’

Dual Opamp Buffered Supply by 1458

There will be instances where the currents from each supply will be unequal. Where this is the case, the resistor divider is not sufficient, and the +ve and -ve voltages will be unequal. By using a cheap opamp (such as a uA741), a DC imbalance between supplies of up to about 15mA will not cause a problem. However, we can do better with a dual opamp (which will cost the same or less anyway), and increase the capability for up to about 30mA of difference between the two supplies.

Fan Controller by 741

The amplifier gets quite hot while in use, so decided to use a fan to cool it. The fan, however, adds a lot of noise. To get the best of both worlds, I thought I’d turn the fan on only when required. The circuit shown uses two forward-biased diodes, one as a sensor diode (at JP2) and the other as a reference diode (D2). The small difference in forward voltage drop is amplified by IC1 and used to drive T1. T1 turns on a fan when the temperature on the reference diode exceeds that at D2. D1 prevents inductive kickback from killng T1. B1 and C2 provide a rectified, regulated supply from the transformer’s auxiliary 12V winding. This prevents noise from the fan motor getting coupled to the rest of the amp.
R1 is used to adjust the temperature cutoff point. This is done by first adjusting it to remain permanently off (turn it both ways, whichever way causes it to turn off, turn it all the way there). Now let the amp run for a while at a reasonably loud volume, so that the output devices heat up. Now place the reference diode on the heatsink of the output devices and back down R1 until the fan just turns on. Make sure that the fan is positioned such that after a while, it cools down the output devices enough to turn itself off.
This and the next circuit are built on the same board, and use the same auxiliary 12V supply, to avoid loading the 78L12 and to prevent fan noise from being coupled into the amp.

Source:http://wiredworld.tripod.com/tronics/mixer.html
Thank you.

Be the first to comment - What do you think? Posted by admin - February 12, 2008 at 10:30 am

Categories: Electronic Control, Motor controller Tags: 741, Electronic Control, Motor controller, Temperature-Control

Microphone Mixer by 741

This relatively simple mixer was designed for three dynamic microphones, but can be re-designed for more or less. Level and tone controls are available to tailor the sound to your needs.

Part
R1, R2, R3 3 1K 1/4W Resistor
R4, R5, R6 3 10K Logarithmic Pot
R7 1 1Meg 1/4W Resistor
R8, R10 2 10K 1/4W Resistor
R9, R11 2 100K Linear Pot
C1, C2, C5, C6 4 0.1uF Ceramic Disc Capacitor
C3, C4 2 22nF Ceramic Disc Capacitor
U1, U2 2 741 Op Amp
J1, J2, J3 3 Input Jacks Of Your Choice
MISC 1 Board, Wire, Knobs, IC Sockets

Source:http://www.aaroncake.net/circuits/mixer2.asp