I made my own speaker protection board for my PL400 Series II. This was made completely out of parts rescued from scrap, except the UPC1237s. I ordered those for a couple dollars shipped from Hong Kong.
I made my schematic based on the UPC1237 datasheet, and values from this project at buildaudioamps.com:
http://buildaudioamps.com/other-audio-related-projects/
I am powering this board off of the display bias in my amp. Before putting it into my amp, I tested the board on my bench with DC supplies. The UPC1237 has a 1-2 second delay when 12V bias is applied. It trips pretty quickly if I put a few volts DC, positive or negative, into either speaker terminal. It latches off once tripped (no auto-restart.)
I was worried about the voltage, and reverse voltage that would appear on the 100uF cap. I thought I probably needed a 100V bipolar cap there. I tested by injecting + and - 30V into the circuit, as if the amp is putting out +/- 30V DC, and the voltage on the 100uF cap never exceeded +/- 0.6V. This verifies that the UPC1237 is clamping, and that small of a negative voltage should be nothing to worry about on a normal polarized electrolytic cap.
I am attaching the schematic and pictures. It seems to work well, but please let me know any comments or potential issues. I went a little crazy with the Zobel networks because all PL400s I have worked on had bad resistors.
I made my schematic based on the UPC1237 datasheet, and values from this project at buildaudioamps.com:
http://buildaudioamps.com/other-audio-related-projects/
I am powering this board off of the display bias in my amp. Before putting it into my amp, I tested the board on my bench with DC supplies. The UPC1237 has a 1-2 second delay when 12V bias is applied. It trips pretty quickly if I put a few volts DC, positive or negative, into either speaker terminal. It latches off once tripped (no auto-restart.)
I was worried about the voltage, and reverse voltage that would appear on the 100uF cap. I thought I probably needed a 100V bipolar cap there. I tested by injecting + and - 30V into the circuit, as if the amp is putting out +/- 30V DC, and the voltage on the 100uF cap never exceeded +/- 0.6V. This verifies that the UPC1237 is clamping, and that small of a negative voltage should be nothing to worry about on a normal polarized electrolytic cap.
I am attaching the schematic and pictures. It seems to work well, but please let me know any comments or potential issues. I went a little crazy with the Zobel networks because all PL400s I have worked on had bad resistors.
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