Electronic – Help tame turn-on transient


I'm working on a dual headphone amplifier. I've discovered that it has a pretty bad turn-on transient that results in a loud pop if headphones are plugged into the amplifier when it is turned on. The split positive and negative rails rise very quickly at slightly different times due to the mechanical action of the DPDT latching switch, S1.

What is the best way to handle this? I figure something that could get V+ and V- to ramp up slowly and evenly at turn-on would solve the problem. Is there an elegant way to accomplish this?

Here is the schematic. BT1 and BT2 are 9V batteries.

enter image description here

original circuit link here

Best Answer

A very simple solution is to put some small amount of resistance or inductance in series with switch (both V+ and V-). All your 0.1uF caps will have a slightly slower RC charge curve and will dampen the transients. Of course you need to balance out the size of the resistor with the current and voltage requirements of your amplifiers. Inductance will choke the transient yet have lower DC resistance. Also ferrite beads can be used which would probably work the best if you pick one that won't be saturated by your inrush current.

Also don't leave your unused op-amps with their inputs floating. If conditions get just right they can oscillate and generate lots of noise.