General Guitar Gadgets Power Supply Issue (turns on every other time?)

[iandy4]

Hi guys,
For a while now I've been using this power supply design for powering my various bread boarded projects rather than breadboard a dual supply each time:

http://www.generalguitargadgets.com/pdf/ggg_bipolar_ps.pdf

The problem that I started to notice a while ago was that when it is used to power my opamp based projects like the one below, it turns on and works as expected but only half the time.  Just about every other time I plug in the power supply, it hums more than usual, I get a radio signals and I hear the guitar if I really crank the amps volume but it's distorted.

Today I decided to isolate the problem which has been bugging me for months.  What I did was plug in the pedal design you see below, powered by the GGG power supply.  I repeated the same action over and over which was having the guitar go into the input of the schematic below and the output to my amp, the GGG power supply is connected to the mains via a 9vac transformer (it uses 7805 and 7905 voltage regulators)  The other side of the GGG power supply (-5vdc and 5vdc) goes straight to the correct power pins on the opamps in the schematic below (and GGG power supply ground to the circuit belows' ground).  What I do to turn the power on and off is disconnect the transformer jack from the GGG power supply's input.  If I leave the amp on and listen I hear four large pops and then nothing.  If I repeat this action over and over, half the time I get guitar as expected the other half I get a veeery low signal with a lot of hum.

When I disconnect the GGG power supply's three output wires (-5vdc, ground, 5vdc) I always get the guitars signal as expected ad no pops when connected and disconnected.  As this is something I'd really like to have other people use, I really don't like how there is a 50/50 chance it won't work every time someone plugs in the transformer to the GGG power supply.  I could add an on/off switch that actually cuts the power between my circuit and the ggg power supplies dc outputs which I know will work but that still leaves the other problem if the pedals power switch is already on and the transformer is connected to the power supply (which is often how people turn on their pedals.)

Any help would be greatly appreciated.  I would love to understand what's happening here and or be able to solve it.  If anyone has something to try I have everything ready to go on the bench!

[iandy4]

What I should have mentioned is that when the circuit works I get the expected 10vdc (-5 + 5vdc) between the opamps + and - power rails.  When I power on and it doesn't work I get 4.9vdc between the opamps + and - power rails.

[PRR]

> I get 4.9vdc between the opamps + and - power rails.

Is that +/-2.5V, or +5V/+0.1V, or what?

In this type bipolar supply, if one regulator comes-up before the other, and the only load is across the two reg outputs, one reg can get "pulled backward" by the other reg, and fail to start correctly. Since it is two half-wave rectifiers, one or the other reg gets powered-up first depending on which half-cycle the power line is on at the instant of plug-in. Hence nearly 50:50 chance, assuming one reg is more susceptable to back-yank than the other.

See bottom of page 14 in the LM340/LM78XX data-sheet. Details are different, but they put two reverse-bias diodes across the outputs to limit yank-back from one reg to the other. See again Fairchild Figure 17.

[iandy4]

Paul, you are my hero! That's exactly what it was.  Thanks for taking the time to send the examples.  I can look into the cause now.  Thanks again!