Regulated/unregulated DC confusion - 9V

[Doug Tymofichuk]

On Tue, 30 Mar 1999 20:28:41 -0800 (PST) Brett Duggan 
<bduggan at netcom.com> wrote:

> 
> 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.
Brett,

The first thing I would do is to check the actual voltage 
output of the wall-wart. I suspect that it may not be very 
close to 9V, if it is significantly higher it could cause 
this problem. You should measure it both disconnected and 
connected to the pedal with the power on. I have seen very 
few _regulated_ wall-warts, if this one is not regulated 
then the voltage could vary by quite a bit.
 
> 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?

It all depends on what voltage the adapter is actually 
regulated at. Besides, a battery is not truly regulated, a 
new 9V battery usually measures about 9.6 volts, this 
voltage slowly drops as the battery ages and develops 
internal resistance.
> 
> 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.> 

This could be something as simple as a blocking diode in 
the circuit to prevent accidental reverse polarity power, 
which introduces a voltage drop of its own.

Maybe the wall wart is defective?

----------------------
Doug Tymofichuk
dougt at cancerboard.ab.ca