voltage drop at power source -what is happening?

cause

You're either not 'well regulated' or you're attempting to pull more current than the regulator can supply.

How about telling us what the device is that you are powering and the specs of the power supply.

If the short is to gnd, you would be reading 0V. So probably an IC got its supply pins reversed or a resistor has a wrong value. When you reversed the supply before you might have killed your circuit. Try to find out if the circuit works with another supply. When you have a multimeter with a DC current range of 2A or 20A you can also measure the current consumption and choose a wall-wart accordingly.

Its an audio modulator. It uses 2x quad opamps (TL074) and some LED/CDs pairs to modify the sound.

Interestingly enough when I pull the chips I read a nice 9V at the plug. Putting in one chip drops the voltage to 3.7V. Bad chip? They aren't getting warm when the circuit is running.

Im using a 9V source that comes from a 7809 and should be able to put out

LED/CDs

plug.

out

would

somewhere?

more

the

One thing you might try is removing the op amp and putting a resistor across the 7809 output which simulates the load. Start with a 100 ohm,

I'm assuming you've got the pinout of the 7809 right. That's another common newbie problem. If you've got a TO-220 package (square black plastic with metal tab), holding the plastic side forward and pins down, the pinout from left to right is

INPUT -- GND -- OUTPUT

Good luck Chris

Good luck Chris

Im not worried about the power supply. I use it for a variety of other applications on a regular basis and it performs well. Its the circuit thats problematic. Somewhere there is lots of power being dumped. I can't seem to find out where though. It seems odd that the problem occurs when the opamp chip(s) are inplace. I might try substituting in another batch of chips to see what happens.

The LM7809 is good to 1 amp but you will need at least 11 volt input to the regulator. You can post a schematic on alt.binaries.schematics.electronic, that would be helpful. Off hand, it sounds like a power supply problem but you have no details.

You might try connecting your power supply to a resistive load to see if it hangs in there. 9v/.5A= 18 ohms would load your supply half way and let you test whether the voltage stays correct. The power dissipated in the load would be

did you scope it for oscillation?

other

circuit thats

seem to

If that amount of power were dumped something must get hot. It's very unlikely that 7809 deliveres more current than possible and therefore output voltage is reduced.

opamp

chips to

Maybe it is your specific load that makes the power supply oscillating. Other loads could be more harmless. Do you have correct capacitors across input and output if 7809 regulator?

Regards