For a quick little Sunday project, I just took an old pair of powered computer speakers and made a little guitar amp out of it by adding a 1/4 input jack. It is powered by a 9V ac adapter. I wanted to also make it portable so I soldered in a 9volt batter clip directly to the ac adapter jack lugs. My question is do I need to unplug the 9 volt battery if I am using the adapter to power the speakers?

 

Probably. Wall warts are notoriously unregulated. They would likely try to charge the battery. That's bad unless the battery is rechargable, and if it is, it needs a regulator for the charging current.
There is a way to use the power jack to automatically disconnect the battery when you plug in.

 

For a quick little Sunday project, I just took an old pair of powered computer speakers and made a little guitar amp out of it by adding a 1/4 input jack. It is powered by a 9V ac adapter. I wanted to also make it portable so I soldered in a 9volt batter clip directly to the ac adapter jack lugs. My question is do I need to unplug the 9 volt battery if I am using the adapter to power the speakers?

Yes. If you don't, you will have whichever of the battery or the adapter is at the highest voltage trying to push current into the other one. If you don't want to unplug the battery every time, you can build a simple switch with a FET or a transistor BJT.

Update: or you could follow #12's even better suggestion to automate the switching

 

I know I could just mount the batter on the outside of the speaker so I could easily unplug it if I need to or I could add a little mini switch to the case, is there another way?

 

Probably. Wall warts are notoriously unregulated. .

Although the ones I have purchased in the last 5+yrs have been SMPS type, it may pay to check the type, a give away is the non-SMPS are usually much heavier.
Max.

 

There is also the idea that TS said, "AC adapter". Those don't mix at all with batteries!

Does that mean AC input or AC output?

 

Probably. Wall warts are notoriously unregulated. They would likely try to charge the battery. That's bad unless the battery is rechargable, and if it is, it needs a regulator for the charging current.
There is a way to use the power jack to automatically disconnect the battery when you plug in.

How would I do the automated switch?

 

How would I do the automated switch?

On a standard DC connector, pin 2 and 3 are disconnected when you insert the plug:

 

Something like this:

 

On a standard DC connector, pin 2 and 3 are disconnected when you insert the plug:

View attachment 80846

That's what I would use. Disconnects the battery when you plug in external power.

Ron

 

I think how I have it is what you are suggesting but I am uploading pics now.

 

Here they are

 

I'm assuming your AC adapter outputs DC with positive on the center pin? In that case, your circuit should work.

Update: that's wrong. See below.

 

yes the pin is positive

 

yes the pin is positive

Hmm, please disregard my remark in post #13, it was wrong. Pins 2 and 3 of the connector are linked by the PCB trace, so your battery would still be connected, even when the adapter is plugged in.

 

Additionally, are you sure the adapter outputs DC? The first thing after the connector on the PCB seems to be a bridge rectifier, which suggests AC.

 

Adapter output is DC 9v 150ma

 

could I break the trace contact between the pins (scratch through it) or does the circuit need those to be bridged?

 

Additionally, are you sure the adapter outputs DC? The first thing after the connector on the PCB seems to be a bridge rectifier, which suggests AC.

Yes the input socket goes to the bridge, at least it will be steered to the correct polarity via the bridge.
Just that you will get ~ 1.5v drop over the diodes.
Max.

 

Note that a standard 9V transistor battery will likely not last long (perhaps a few hours for an alkaline type) in powering your amp.