Controlling volume

[nicksydney]

Hi,

I bought this MP3 board http://www.ebay.com.au/itm/172304337841 and was wondering whether it is advisable to use a normal potentiometer (something like this  http://www.ebay.com.au/itm/5Pcs-10K-OHM-3-Terminal-Linear-Taper-Rotary-Volume-B-Type-Potentiometer-Pot-/161947336328 ) to control the volume ?.

Thanks for the help

[Brumby]

Assuming you want to control the analogue output, couple of things...

1. It depends on the impedance of the device you want the controlled volume to go to.  For speakers around 4 ohms to 8 ohms - forget it.  You will have one point with full volume and the rest of the rotation will result in nearly nothing audible.  For headphones with 30-odd ohms impedance, it won't be much better.  However, if you are feeding it into another amplifier with an input impedance in the order of 10K or more, then a 10K pot will work.  To make a simple volume control like this work, you generally need a (comparatively) low source impedance and a potentiometer and load with higher impedances.  If you can wrangle the maths, you can put together a tailored solution.

2. For audio volume control, logarithmic pots are the way to go.  A linear pot won't have the range of control you are used to, since our ears respond to sound intensity on a logarithmic scale.

3. If you want to control a stereo signal, you will need a dual gang pot.

[nicksydney]

Assuming you want to control the analogue output, couple of things...

1. It depends on the impedance of the device you want the controlled volume to go to.  For speakers around 4 ohms to 8 ohms - forget it.  You will have one point with full volume and the rest of the rotation will result in nearly nothing audible.  For headphones with 30-odd ohms impedance, it won't be much better.  However, if you are feeding it into another amplifier with an input impedance in the order of 10K or more, then a 10K pot will work.  To make a simple volume control like this work, you generally need a (comparatively) low source impedance and a potentiometer and load with higher impedances.  If you can wrangle the maths, you can put together a tailored solution.

I have this speakers (http://www.ebay.com.au/itm/252339609828) which it says rated 4ohms which is a very low impedance. What if the output is hook up to this kind of amplifier (http://www.ebay.com.au/itm/191932913646) and then the output of that amplifier is hooked up to a log pots as indicated, will that works ?

[Brumby]

OK - Now you have some things that could work.

The arrangement would be:  MP3 module --> Potentiometer --> Amplifier module --> speakers.

I would take the headphone output from the MP3 module, but the level might be a bit high to give you a good range on the potentiometer - which isn't a big problem.  A couple of resistors can fix that.

From the speakers you have indicated, I wouldn't expect a great sound - but you should get a result that works.

[nicksydney]

OK - Now you have some things that could work.

The arrangement would be:  MP3 module --> Potentiometer --> Amplifier module --> speakers.

I would take the headphone output from the MP3 module, but the level might be a bit high to give you a good range on the potentiometer - which isn't a big problem.  A couple of resistors can fix that.

From the speakers you have indicated, I wouldn't expect a great sound - but you should get a result that works.

Great. Will give it a go and get the amplifier module. Thanks for the help

[Audioguru]

The MP3 player has the IC number rubbed off so you cannot look up its details that are not told on ebay. It has push buttons for its volume control but we do not know the volume setting when it is turned on. Muted? Full blast? If its volume is turned down when it is turned on than your external volume control and amplifier will be useless. The tiny speaker will sound awful and it also has no detailed spec's.

[Brumby]

The MP3 player has the IC number rubbed off so you cannot look up its details that are not told on ebay. It has push buttons for its volume control but we do not know the volume setting when it is turned on. Muted? Full blast? If its volume is turned down when it is turned on than your external volume control and amplifier will be useless.

That's a valid point.  I would think (hope) the initial level would be non-muted, but there is always the possibility it might be.

[Brumby]

The tiny speaker will sound awful and it also has no detailed spec's.

I was being diplomatic...

From the speakers you have indicated, I wouldn't expect a great sound

... but you are right.

[nicksydney]

The MP3 player has the IC number rubbed off so you cannot look up its details that are not told on ebay. It has push buttons for its volume control

The ++ and -- button works for moving to next and prev track (MP3) it does not control volume

[Brumby]

Those buttons are marked:
Next/V++
Prev/V--

They are dual function, depending on the Mode.

Next = Next track
V++ = Volume Up
Prev = Previous track
V-- = Volume Down

[Brumby]

I assumed you wanted an old-fashioned volume control, in which case what I said stands .... but if you only wanted some way of controlling the volume, then that's already built in.

It's a basic function that is somewhat necessary for a practical module.

[macboy]

A linear taper pot can work fine for audio volume control, provided you add one extra resistor to make it closer to a logarithmic taper. In fact, the taper on this can be even more desirable than a true linear pot. Refer to Elliot Sound Products project number 1 here.

Of course, with audio, we are usually talking about stereo. You probably want a single dual-gang pot rather than two single pots. Again you can choose a dual linear type used as above or a dual log pot, which is actually quite common and easy to find as they are often used for exactly this purpose.

If your MP3 module contains push-button volume control, this is almost certainly implemented digitally, which is not desirable. It will mathematically reduce the amplitude of the audio samples prior to the digital to analog converter (DAC), so that when listening at anything less than full volume, only a fraction of the dynamic range of the DAC is used, but you still get all the noise that it produces. It's better to run the DAC at or near full volume, then into an attenuator (a volume control pot) so that you also reduce the noise as you reduce the signal.