suitable potentiometer for 8 ohm 0.5W speaker

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Liran
 
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suitable potentiometer for 8 ohm 0.5W speaker

Post by Liran »

Hi,
I bought this speaker from adafruit:
https://www.adafruit.com/product/1890

I soldered it to PAM8302 2.5W Class D Single Channel Audio Amplifier and the amplifier i soldered to the raspberry pi 3 board as in this image:
https://cdn-learn.adafruit.com/assets/a ... 1453083991

now It all works well, but I have no idea how to turn down and up the volume, I guess I need to put a potentiometer between the raspberry pi and the amplifier, or between the amplifier and the speaker, but what is the value of potentiometer I'm looking for? how is it callculated? do I need a potentiomenter, or do I need some other component?

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adafruit_support_bill
 
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Re: suitable potentiometer for 8 ohm 0.5W speaker

Post by adafruit_support_bill »

A pot between the Pi and the amp input would allow you to control the volume. 10K is a good value. a "Log" or "Audio Taper" pot is better suited to volume control than the more common "Linear" pots. We have a few Log taper pots in the store. For a mono amp, this single-channel log pot would do fine:

https://www.adafruit.com/product/3391

Connect one outer leg to GND and the other outer leg to the Pi signal output. Then connect the center "wiper" pin to the input of the amp.

We have knobs for the pots as well: https://www.adafruit.com/?q=knob&p=1

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Liran
 
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Re: suitable potentiometer for 8 ohm 0.5W speaker

Post by Liran »

I'm a bit confused, I have an A+ and A- in the amplifier, when I use your instructions how can I connect the A-?
I came out with this circuit: (attached file)
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adafruit_support_bill
 
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Re: suitable potentiometer for 8 ohm 0.5W speaker

Post by adafruit_support_bill »

These are single-ended signals, so A- and GND are pretty much the same thing. But if your Pi has an A- pin, it will probably be a bit less noisy than the common GND pin. You can just move the black wires on your diagram to connect to A- on the Pi and amp instead of GND.

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Liran
 
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Re: suitable potentiometer for 8 ohm 0.5W speaker

Post by Liran »

I actually connect to the pi using this picture from Adafruit:
https://cdn-learn.adafruit.com/assets/a ... 1453083991

I have no idea if this is an A- , I'm just assuming, I also assume that the A- is closer to the HDMI..
:) all this is because of one picture.

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adafruit_support_bill
 
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Re: suitable potentiometer for 8 ohm 0.5W speaker

Post by adafruit_support_bill »

It would be helpful if you provided a link to the tutorial that came from.

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Liran
 
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Re: suitable potentiometer for 8 ohm 0.5W speaker

Post by Liran »

hi, sorry for late response,
I did what you said, and it worked, though I used 10k ohm Slide pot (linear) because this is the only one i can find which fit my project.
I have found out that all Log pot are too big, and they do not make small 10k pot. only slide pot can fit the project.
if know of Log pot which is small, I would be happy to buy it =)

on thing though, though I used the slide pot, I am getting a very low sound when I am on the maximum volume... seems like it doesn't give the full power if I use 10k.

so I guess I need a number smaller then 10k... i need it about half stronger in sound (if i don't use the pot, i get half more louder sound). is it a good math? or I missing something?
:/

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Re: suitable potentiometer for 8 ohm 0.5W speaker

Post by adafruit_support_bill »

When the pot is at max volume, the resistance through the pot should be very close to zero. So the volume should be about the same as with no pot at all.

If you have a multimeter, disconnect the pot from the circuit and slide it all the way to one side. Measure the resistance between the center pin and the end pins. It should be close to zero at one end.

Then slide it to the other end and measure again. It should be close to zero at the other end.

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