Chip amp power supply

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
This is one of my first real attempts at a diy amplifier.
I assembled this earlier today as shown with 6800uF 56V capacitors and 500ohm 3 watt resistors. I powered it up with no load and the resistor on the negative rail burned. I am guessing.... Without a load, the current flowed through the resistor. Can this type of PSU not be powered without a load? Were the resistors not enough wattage? Were the capacitors too low of a rating? Should I have fuses in series on the two feeds from the transformer?


  • psu.bmp
    24.1 KB · Views: 100
Last edited:
So the Vcc value is ~48V?
Ohm's law to the rescue. If there are 48 volts across 500 ohms, nearly 100 milliamps will flow through the resistor (48/500=0.096). Power is voltage times amperage so 48*0.096=4.608. Your circuit puts about 4.5 watts into a 3 watt resistor.
Were the resistors not enough wattage?
was the correct question.
The capacitors' WVDC should be fine - there's 10+% margin there, though some may prefer it closer to 20%. The transformer should be fused on the primary side.
OK> This is beginning to come together for me. As an automotive technician, Ohms law gets ignored quite a bit. A lot of guessing based on experience. In school were taught to use ohms law to zero in on almost anything from 5 feet down a wire. In the field it gets thrown to the wayside. Thanks for the refresher and for giving me back some fundatmentals that I will hold on to. I googled Vcc and did not find it. What exactly is Vcc and how is it calculated?
I understand. Ohm's law is useful enough that it's best to hold it close so it only burns you when it isn't accurate.:)
Vcc is the label for the outputs on your power supply. It isn't calculated as much as just determined from the particular circuit. I don't remember exactly, but I believe the term arose as symbolizing the collector voltage on a transistor. It's use spread to include any general supply voltage, whether BJTs were included in the circuit or not.
The only thing that could be wrong here is that a capacitor could be leaking. I had a receiver that was going into overload. The previous technician snipped all of the output modules searching for a problem. I was curious about the 6800uF capacitors because there was a very slight bulge on them. At $14 per output module I decided to scrap the $30 receiver. I salvaged the suspicious Capacitors without testing. How do I test capacitiors? What do I need? Capacitance tester and ESR tester?
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.