controlling gain/volume on an amp board

Other Hardware General Electronics
1

I found this incredibly good quality amp for less than $1!!! it works great but it does not have any volume control, would anybody know how to put volume control on this board output with the most power consumption efficient way? Here is the board

edit: Do I put a potentiometer on the power in or the audio out?

a second question, this board was meant to power speakers, I am using it with headphones for someone who is hard of hearing. My question, is that I assume the load of headphones are much lower than speakers which it was designed for... How does this affect the performance of the board, does it cause it to overheat or anything like that?

Thanks

2

Here is a similar product, you get what you pay for:

You could put a series resistor/pot in the output to the headphones to adjust the volume.

This is the other stuff that eBay store sells, do you see any problem here?
http://stores.ebay.com/chesksstore?_trksid=p2047675.l2563

3

thanks Larry, The board I have works surprisingly well. No pot, but no prob on installing one myself. The reason i asked about where to put the pot is that if I put the pot at the vin, I thought it may conserve power, If I put the pot at the audio out, does that effectively doing the same thing...increasing resistance and therefor decreasing power flow? a question from a layman....

what about the effects of powering headphones vs speakers? How do I measure the ohm rating of my headphones?

and on the adafruit description, it talk about differential output.. what does this mean?

4

joefly:
Do I put a potentiometer on the power in or the audio out?

Neither actually.

In almost all devices, the volume control potentiometer (usually around 10k, and generally logarithmic) goes on the signal input to the amplifier.

As so often happens, you have given less than half the information required to answer it. The other parts are: What is it you need to amplify? You might not need any further amplification for headphones. Why would you want a 3 watt amplifier for headphones? This would be just as useful.

The impedance of headphones (or speakers) is generally not much more than what you measure with a multimeter.

Differential output means you drive one channel with the opposite signal to the other and connect the speaker between both outputs to get (if the amplifier is capable) four times the power.