I recently had the opportunity to work on another Pioneer PL-250 turntable. The previous owner was having an issue with the platter moving back and forth without continuously rotating, which can be a frustrating problem to deal with. After a quick inspection, I found that the issue was caused by some faulty electrolytic capacitors (3 × 470µF) near PA2005 and a bad bridge rectifier. These components were preventing the platter from spinning smoothly in the right direction. Fortunately, I had the necessary replacement parts on hand, so I quickly swapped out the bad components. Once the new capacitors and rectifier were in place, I gave the turntable a full service to ensure that everything was working as it should. After completing the repairs and maintenance, I tested the turntable and was pleased to see that it was now spinning smoothly and continuously in the correct direction.
This project is about a single-channel microphone echo generator circuit. This circuit builds around the Holtek HT8970 echo effect generator IC. It offers complete control of the echo effect by providing delay, mix, and output level adjustments. HT8970 is an echo/surround sound effect generator IC with 20Kb SRAM. It also contains the built-in VCO stage, AD, and DA converters. The chip costs less than 0.5 US$ and is commonly available in the market. Prototype build of the echo effect generator circuit. The given schematic offers a maximum of 320ms time delay and works with a single-rail 9V DC power supply. In addition to the HT8970 integrated circuit, this circuit uses an NJM4558 op-amp to amplify the input and output audio signals. HT7150 voltage regulator uses in this design to power up the HT8970 IC. The HT7150 is a low-power 5V regulator IC from Holtek, the same maker of the HT8970 IC. Top view of the prototype build. The circuit designs to work with 500Ω dynamic microphones.