TPA3125D2N based Class D guitar amplifier

Thread Starter

Austin Varughese

Joined Feb 9, 2018
7
I intend on building an power amplifier as a summer project and I don't have an electronics background so pardon any questions that appear to be stupid.
The amp that I want to use has four gain configurations and on it evaluation board these configurations are adjusted with the help of a pair of shunts.

What I wanted to know is what would happen if instead of the shunts I used a potentiometer to vary the gain of the amp ?
Would it be big and stupid noob mistake or is it a good idea.
 

crutschow

Joined Mar 14, 2008
34,285
What I wanted to know is what would happen if instead of the shunts I used a potentiometer to vary the gain of the amp ?
It's a noob mistake. ;)
That's a two bit digital (binary) input so you can't use a pot.
If you do need to change the gain frequently for some reason, you could replace the shunts with two switches.

If you want a pot gain control, you can do that at the two audio inputs, LIN and RIN.
The pots should be 10kΩ audio type, not the common linear type.
For mono you can use one pot feeding both inputs.
For stereo you would use a two-gang pot.
 

Thread Starter

Austin Varughese

Joined Feb 9, 2018
7
It's a noob mistake. ;)
That's a two bit digital (binary) input so you can't use a pot.
If you do need to change the gain frequently for some reason, you could replace the shunts with two switches.

If you want a pot gain control, you can do that at the two audio inputs, LIN and RIN.
The pots should be 10kΩ audio type, not the common linear type.
For mono you can use one pot feeding both inputs.
For stereo you would use a two-gang pot.
But won't those act as volume control rather than gain??
 

bertus

Joined Apr 5, 2008
22,270
Hello,

Yes, the potentiometer will work as a volume control.
The 2 gain setting inputs can set the maximum volume.
Select a setting that will have no distortion at maximum volume of the potentiometer.

Bertus
 

ElectricSpidey

Joined Dec 2, 2017
2,758
Gain is an amplification factor.

Volume is a “level” control.

Normally you would not use gain to control volume unless you have AGC.

Ideally you want the gain to remain constant, over the entire volume range.
 

crutschow

Joined Mar 14, 2008
34,285
But won't those act as volume control rather than gain??
The pot will change the gain from the input of the pot to the output of the amp.
It won't, of course, change the gain of the amp, which is controlled by the two digital inputs.

Why do you want to change the gain of the amp with a pot (which also changes the volume)?
 

Thread Starter

Austin Varughese

Joined Feb 9, 2018
7
Treating it as a black box, explain the difference between
The pot will change the gain from the input of the pot to the output of the amp.
It won't, of course, change the gain of the amp, which is controlled by the two digital inputs.

Why do you want to change the gain of the amp with a pot (which also changes the volume)?
Foolishness I think. ;P
Thank you everyone for your answers and help. :D
 

MrChips

Joined Oct 2, 2009
30,714
Remember, this is a project to build a guitar amplifier. My guitar amp has four knobs to adjust volume:
GAIN, DRIVE, LEVEL, MASTER.
Then there is fifth knob on the guitar itself. That one makes sense because you don't want to have to reach far to adjust the volume. I could never figure out the difference between GAIN and LEVEL.
As far as I know, you want to increase the input level at some stage to determine when the amp clips the signal. That doesn't matter much to me because I prefer a soft and mellow sound, jazz style, and not heavy metal rock.
 
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