Audio amp volume control?

[binsky33333@verizon.net]

Hey guys, been doing some research on amps lately. I've been looking around, and ive found tons of good info. Now i just have a question on how to control volume. Obviously volume will be controlled using a potentiometer. How where does this potentiometer go? Does it go where you adjust the gain on the amp? Does it go between the input of the sound source and the amp? Does it go between the speaker and the amp? Hope someone can answer this simple question!

Thanks!

 

[MikeMl]

Usually on the input.

 

[binsky33333@verizon.net]

And what kidnd specifically of potentiometer would i use? Just the ones i find at radio shack? And would a 10k be good?

 

[audioguru]

Your hearing's response to loudness is logarithmic so you can hear a whisper and hear loud music at a rock concert.
So the volume control should also be logarithmic which sometimes is called "audio taper".

You do not want a linear potentiometer.

I have seen many speaker amplifiers but I have never seen one that does not have a volume control. Maybe the volume control on your amplifier is mis-labelled as its "gain control".

 

[unix60959]

i would wire the pot as a rheostat, which mean that only one outside leg and the middle leg are connected and put it in series on the input. also make sure its logarithmic and not linear

 

[audioguru]

A rheostat in series with the input of an amplifier cannot reduce the volume much.

 

[EN0]

Normally, the pot is within the feedback loop of your op amp.

 

[audioguru]

A gain control is the feedback resistor.
A volume control is at the input of an amplifier.

 

[binsky33333@verizon.net]

Ok cool. Thanks guys. Now I just have a few more questions. Will volume control limit the amp output in wattage, and does limiting the gain lower the amp output in wattage? Also can the gain of an amp be over 100? Btw I'm using the tda2002 amp. Also how do you calculate amp output in wattage? Is it ampwatt x (speaker impedance / amp impedance rating)?

Thanks guys!

 

[EN0]

A gain control is the feedback resistor.
A volume control is at the input of an amplifier.

Thanks for that clarification, AG.

 

[audioguru]

I'm using the tda2002 amp.

The TDA2002 amp is obsolete and is not made anymore. It was replaced by the TDA2003 that has improved performance.

Will volume control limit the amp output in wattage, and does limiting the gain lower the amp output in wattage?

The volume control can turn down the output power to zero. It is used to adjust the loudness of the speaker. At a certain input level the volume control or gain control can cause the output to clip and produce severe distortion for louder signals.

Can the gain of an amp be over 100?

Usually a power amplifier does not have too much gain so that it has plenty of negative feedback to reduce distortion. A preamp can add more gain.

How do you calculate amp output in wattage? Is it ampwatt x (speaker impedance / amp impedance rating)?

A speaker power amplifier has an extremely low output impedance (0.04 ohms or less) so that it damps the resonances of a speaker.
Manufacturers of amplifiers lie and exaggerate the power number by saying the power output when the output is severely distorted (10% distortion) and is clipped into a square-wave.
Frequently a power amplifier manufacturer advertises PEAK or MAXIMUM power which is simply double the RMS number.

The TDA2003 amp is rated for an output power of 6W into 4 ohms or 10W into 2 ohms when the supply is 14.4V and when the input level is too high producing horrible 10% distortion.
Frequently it is used with a 12V power supply then its output is only 3.2W at clipping with a 4 ohm speaker. With an 8 ohm speaker the output power at clipping with a 12V supply is only about 1.8W.

The output power at clipping is calculated by the peak-to-peak voltage of the output sine-wave divided by 2.828 which gives the RMS voltage of the sine-wave which is squared, then divided by the speaker's impedance. So the p-p output with a 12V power supply is 10.12V then the RMS voltage is 3.58V which is squared to 12.8 divided by 4= 3.2W.

 

[binsky33333@verizon.net]

Ok cool, thanks! Ill look into the TDA2003. Also what is clipping? And can i use the same schematics for the TDA2003 as the TDA2002?

 

[audioguru]

Ok cool, thanks! Ill look into the TDA2003. Also what is clipping? And can i use the same schematics for the TDA2003 as the TDA2002?

A TDA2003 is also getting old and has fairly low output power. Use a TDA7240A that has two amplifiers inside to drive each end of a speaker in a bridge. Then the output power is about 3.5 times more.

Clipping is when the output of an amplifier goes up and down to voltages that cannot be exceeded due to the power supply voltage. Then there is severe distortion because the waveform has flat spots at the top and bottom.

The detailed schematic and usually a recommended pcb design are on the datasheet of almost every amplifier IC.

 

[binsky33333@verizon.net]

Ok cool! Thanks! Also, i dont think i need a 20 watt amp. Im only going to be running two 6 watt speakers.

Also what TDA amp should i use for a 28 watt speaker?