I've been tagged (volunteered actually) to assist a group with their sound system. Boom boxes with removable speakers are good for this, but sometimes you need a bit of amplification between the wireless mic receiver and the main amplifier.
This design has a variable gain between 1 to just over 20. I measured a max gain of 21.7. I made the lid using a 3D printer, which was a luxury. You can adapt the dimensions given to a conventional lid. For those lucky souls who have access to a 3D printer I included the .stl file.
The frequency response was flat up to 100Khz, and I saw low role off around 20 Hz (theoretical is 16Hz).
Here is the breadboard and schematic:
The parts not on the parts list were:
Project Box - BG Micro Part Number ACS1157 ($2.01)
Wall Wart DC Power supply - 9VDC to 18VDC
Matching Power Input Jack for wall wart
U1 - NJM4565 (I suspect almost any decent dual op amp will work, but this one is designed for low noise).
This project is very low power, almost any DC wall wart in the voltage range will work. Do make sure the wall wart is completely isolated from the AC line. I have made a prototype before this one shown which will be recycled, and will make 2 more before I am done. I was aiming for maximum simplicity as well as performance.
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