I assembled one of these Jaycar kits DIY MM Phono Preamplifier Kit (Moving Magnet) When I plugged it in the right channel worked fine the left obviously had some issues. There was a major hum and a rythmic clicking sound. I checked it with my meter. When I turn it on it has about 2 volts but increases over a minute or so to at least 11 volts. I haven't left it on long enough to see where it stops but I'm guessing somewhere around 12. I have two of these kits so I swapped out the chips and caps one by one and have not solved the problem. I'm hoping that the increase in voltage over time is a clue to what component is bad. Any ideas? Thanks, Scott
I have check the voltage from the supply and I have 24 volts across the chips pins 4 and 8, exactly what the manual says I should.
I have check the voltage from the supply and I have 24 volts across the chips pins 4 and 8, exactly what the manual says I should.
You might try lifting one end of the input capacitor to the right hand IC. Check voltage across the 47 microfarad capacitor at the negative input to that amplifier.
There should be zero volts on the outputs of all amplifiers, as the inputs are referred to ground and the negative inputs are only connected to the outputs. If the output drifts toward the positive supply, either the positive input is going positive or the negative input is going negative. Maybe the 7.5k resistor is open or not properly soldered.
There should be zero volts on the outputs of all amplifiers, as the inputs are referred to ground and the negative inputs are only connected to the outputs. If the output drifts toward the positive supply, either the positive input is going positive or the negative input is going negative. Maybe the 7.5k resistor is open or not properly soldered.
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