DC Transformer Noise Reduction?

[Jack.Straw]

Hi.  I'm having fun building these "Ruby" practice amps from runoffgroove.com.  I've wired it with a switching DC jack that cuts off the battery when I plug in a 9v wall transformer.  The only problem is that the transformer introduces hum into the circuit.  I've used shielded wire for all connections, and have even wrapped the circuit itself in copper foil tape with conductive adhesive (touching ground).  I'm stumped as to what else I can do to get rid of the transformer hum.  Any ideas?

Here is the circuit:
http://www.runoffgroove.com/ruby.html

And this writeup shows how the DC jack is wired in:
http://www.generalguitargadgets.com/pdf/ggg_ruby.pdf

Thanks for any advice you can offer,
-Scott

[phatt]

Hi Jack,
Yes frustrating as no one mentions that these things need a well regulated PSU.
You can add another Electro can right before your amp.
Maybe add a 100 ohm resistor in series right before the cap.
have fun, Phil.

[joecool85]

Phil has the right idea, if that doesn't work you can try a 220uF cap along with a 10uF or smaller after it.  Supposedly helps with ripple, haven't tried it myself as I just run mine on 9v battery power.

[Jack.Straw]

Awesome, thanks guys.. I'll give that a try tonight!