Power supply for Little Gem

[zener]

Just finished putting my Little Gem in a plastic box with a size if 4"x3"x1.25".  It's great.
I use a power supply that can switch between 3, 4.5, 6, 9 ans 12v., 750mA - 1A written in the label. When I use a 9v battery, it's so quiet while with the power supply, there's a small hiss or buzz while i turn the volume knob. Though the noise is not really audible, I want it to fix it to make it sound like that powered by a 9v battery. I'm using a small karaoke set as an auxilliary.

Thanks for any help :wink:

[smoguzbenjamin]

Try putting a high value cap across the + and - of the PS input.
Works for me!

[zener]

Actually, there's already a 1000uf cap and 1K resisitor across the power lines. I can't post the schematic but here's the arrangement of the parts:
220v - transformer - rotary switch - 4 1N4001 diode - 1K resistor and 1000uf across + & -.

Isn't the 1000uf large enough?

[javacody]

Zener, Peter Snowberg advised me to use a 0.1 uF cap across the rails to eliminate more noise. I did so and also opted to use a 0.01 uF cap as well (in parallel to the 0.1uF cap). This seems to have worked very well.

[smoguzbenjamin]

Congratulations! I'll be making a little gem if I can ever get some 386's...

[zener]

Javacody, do I have to take out the 1000uf or just add the .1uf cap across?

[javacody]

Leave the 1000 uF (in my Little Gem, it is a 470uF but I think bigger is better here) and place a 0.1uF in Parallel to it. You may actually want to do this on the board, to eliminate any hum picked up by the power supply cable. You would just place the 0.1uF cap going from +9 to ground.

[zener]

Thanks for the tip. i'll try that after few hours. It's 4:30 in the morning here. I might wake up the neighborhood  :? :shock:  :roll: .

[smoguzbenjamin]

Turn the volume control real quiet. Or otherwise get some sleep, you might need it if you've been up all night