Why is unloaded buffer showing an offset? – I am using an AD8041 IC as a buffer for a 0.2 Vpp sinewave input at 1 kHz from the function generator. The circuit is set on an NI Elvis II+ board. The buffer is unloaded but there occurs some offset at the output of the buffer. Why is this happening? Read more

Eliminating feedback oscillations in PA audio circuit –  I need suggestions for a circuit to put between a microphone and a power amp that can eliminate auto oscillation. The audio system is set up in a church built in 1130 and I can’t see any other way to eliminate positive feedback due to the acoustic of the interior. Read more

Car audio amplifier and multiple speaker outputs – I have a car radio that I’d rather not tamper with it but I want a decent aux hookup. I bought these stereo amplifiers and am wondering how to hook it up to all four speakers at the same time as the radio. At first I thought of a way to switch the speaker inputs from amp to radio and back, but an 8-channel switch seemed crazy. The other method seems to be to hook both systems up as constant inputs, but have something in place so that the amp output cannot reach the stereo, and vice versa. Read more

Op amp voltage question – I am simulating an op amp 741 as a unity gain inverter in Proteus. When the signal input is AC with 10 mV amplitude, the output signal is okay. But when the amplitude is 1 V, I get a distorted output waveform as shown in the figure (2) below. Can anybody explain how to correct this? Read more

Low power IC for charge pump and single pulse? –  I am making a special type of indicator to help me find my keys on the darkness. Usually Tritium-based indicators would be used but I do not want to use them. The solution I found was to use a hybrid system. What I need to do is somehow detect when a pulse comes from the switch and then light up the LED. Then for some time (seconds) do not light up the led, even if a second pulse comes. This will save a lot of battery life but the detection circuit must draw very very little power to prolong the small button cell (AG1) battery life. I also need a suitable charge pump to step up the voltage from 1.2-1.5v (button cell) to 3-3.2v. I could use just two batteries in series, but if a very low power IC exists, then a one-battery booster can be made. Any ideas for such a low-power IC? Read more

Output voltage swing of voltage amplification – I have a question about the voltage amplification stage of an (audio) amplifier. I just took this attached schematic as an example. The VAS (Voltage Amplification Stage) transistor Q4 is driven by the output current from the input pair. The VAS is a transimpedance stage, converting a current input into a voltage output. But where does this output voltage originate? For example, in the case of a simple common emitter amplifier with a load resistor in the collector path, the collector current is converted to a voltage by this load resistor. That’s easy to see. But how does this work in this schematic, where the load is a current source combined with the output load buffered by the emitter followers. And where in this schematic is the voltage “created” to provide the output voltage swing to drive the load? Read more

Variable mode power supply – I am looking for variable power supply with an output range 0 VDC to 24 VDC with constant 250 mA current and an input voltage 25 VDC. Read more

Design of hybrid power supply system – I have a laptop of 19.5V, 3.34A and a receiver of 14V, 4.5A. I need to design a hybrid power supply system using a solar panel and a windmill. What specifications should I consider with regards to the solar panel and the required battery, as well as the windmill? Read more

Measuring the IIP3 and RFDR of a complex filter – I just designed a active-RC complex filter based on TT biquad and work for GPS or compass receiver. The filter has four ports including two in-phase and two quadrature inputs. The in-phase consists of two AC signals: Mag 1.0 Phase 0.0 and Mag 1.0 Phase 180. The Q-phase are Mag 1.0 Phase 180 and Mag 1.0 Phase 270. It seems that there are many test methods available. Which is the best?  Read more

Broadband impedance matching problem – Is it possible to match a 500 KΩ output to a 50 Ω load over a broad frequency range of 0.5 – 7 GHz? Read more