Music Tech DIY • Re: Bench power supply

Check to make sure you are using the correct regulators? It's an easy mistake to use the same one on both sides but there is one for positive voltage and a different one for negative voltage. Also make sure you are using an AC wall wart, not a DC one. I didn't notice anything that looked wrong.

You can quickly find the problem point by measuring the AC and DC voltages on the negative side at each point in the circuit. Start at the AC input, then check for the unstable DC at the input of the regulator, then for stable DC at the output of the regulator, etc. etc.

Thanks. The voltage regulator (L912CV) seems to be the culprit. I replaced it and got similar results, so perhaps I have a bad batch of those. Re-ordered.

Seems like the L912CV you stuffed in there has a different pinout as the LM7912 the PCB layout calls for... Having pins 3 and 2 reversed. So input and output on different pins. That's what came up, when i did a quick research for both regulators pinouts.

And additionally a heads up to not connect both a 78XX and 79XX regulator on the same heatsink, unless using insulation as the big heat transmitting surface on their back is on the positive regulators the 0V and on the negative regulators either the DC input or output and as such would create a nice short and magic smoke.

Statistics: Posted by aspertime — Sun Mar 17, 2024 1:54 pm