This report describes the operation and adjustment of a Phase Locked Loop hum cancellation circuit that can be used to reduce the residual hum from any amplifier. Normally this is useful for DHT amplifiers with AC operated filaments, as even with a hum balancing potentiometer, there is a residual hum component at twice the line frequency that is u
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navoidable, even with perfectly filtered HT voltage. However, it may be applied to any amplifier. I`ve reported a hum cancellation circuit (here) that provided improvement in hum performance of many DHT circuits. Some people have used this successfully, some with only limited success. The key is to get the amplitude and phase set just right to cancel the residual hum component. This is not always easy nor convenient, so I sought a way to make this concept more universally applicable. This report describes the results. The key behind this version is the use of a phase locked loop, fed from the mains supply (50 or 60 Hz). A PLL consists of a phase comparator, a loop filter and a voltage controlled oscillator (VCO). The phase comparator compares the phase and frequency of an incoming signal (the line frequency, not the "music" source) against an oscillator, and adjusts the oscillator frequency so that it equals the incoming reference. In this case, the VCO operates at 16 times the line frequency (800 or 960 Hz), which is divided by 16 and compared to the line frequency. The x16 allows the line to be split into 16 equal portions. For simplicity, I opted to split this into 8 equal portions, each of which separately control a trimmer pot. The portions are summed and filtered to produce a cancellation signal that can be used to compensate for an arbitrary phase and amplitude of the residual hm signal to be canceled. The filter...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
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In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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