Regulated/unregulated DC confusion - 9V

[Brett Duggan]

Hello all,

I am having some difficulty understanding a situation I have experienced 
with my semi-old Boss CE-2 analog chorus pedal, and was hoping someone 
here could help me.

For power, this particular effect can use either a 9 Volt battery or an 
unregulated 9V DC (200mA) wall-wart adapter.  With a 9 Volt battery, 
the pedal works great.  Now, I didn't have an unregulated 9V DC adapter 
of correct polarity at hand, so I tried using a regulated 9V DC 400mA 
adapter with it.  When using the adapter, I noticed that distortion 
occurred whenever the audio signal going into the pedal was hot.  This 
distortion did not occur when using the battery.  Also, the "effect on" 
LED works fine with the battery but does not work with the adapter.

What I don't understand is this...I thought a battery was a regulated DC
power source.  If this is the case, then how can the battery provide
headroom that the regulated DC adapter apparently cannot?

The only clue I have to a difference between the two power sources is that
it looked to me like the negative terminal of the battery was connected to
ground, but the negative pin of the DC input jack connected to some point
on the PCB.  I was unable to trace this connection any further.  I'm
tempted to buy the schematics for it from Roland just to satisfy my
curiousity. 

Anyway, if you can help me understand any of this, I'd really like to 
hear from you.

Thank you very much for any help!
Brett D