Potentiometer Before or After Amp? Why?

[RxBrad]

So, I currently have my GBZ audio wired up as Pi -> PWM circuit -> PAM8403 Amp -> 10k pot -> headphone jack -> speaker. Everything works great. Volume smoothly controls from the bottom to the top range of the pot at levels that seem appropriate. There is no buzzing or static at all. Everything just seems great.

However, I keep seeing warnings online that the pot should always go BEFORE the amp? But WHY??? Will there be excess power usage? Will the pot fry? Or does it just limit the maximum volume produced (in which case, I'm totally happy with what I have)?

[Cookiemonster]

When putting the potentiometer in the output line of an amp, you can overload the potentiometer.

On higher audio levels with low impedence speakers, dead spots in the volume range can appear.

Also Magic black smoke will appear on serious overloads.

Iam sure placing it after the amp will be just fine in this low power setting.

Its like revving up the engine of a car wile driving and govern the speed with the brake pedal..

[RxBrad]

Thanks, @cookiemonster.. that all makes sense. I spent the afternoon rewiring my GBZ to put the potentiometer before the amp. Unfortunately, the sounds quality went from "perfect" to "hot garbage". I think it's possibly because the pot sits right on top of the screen PCB, and it picks up tons of interference before going to the amp. The volume seems a lot louder now, too; and it maxes out after about a quarter turn instead of gradually increasing as you turn the volume up.

I guess I'll go back to doing it the wrong way. It just seems so much better.

[Cookiemonster]

I think i know what is the couse of your problems.
The potmeter should have the output signal of the DAC on the leftmost pin, output to AMP middle (slider), and GND on rightmost pin.
That way you will generate a voltage divider over the whole range.

[RxBrad]

I'm actually using both channels on this particular amp, so I have a dual gang 10k pot.

For my good working sound, I had:
PWM Audio Circuit L/R to Amp L+/R+ IN
PI/PWM GND to Amp GND IN

Amp L/R+ OUT to Pot L/R IN
Amp L/R- OUT through 100uF cap & 10ohm resistor before merging into Pot GND (because L and R from this amp are not on common ground)

Pot L/R OUT to headphone jack L/R in
Pot GND to headphone jack GND

Headphone jack L/R OUT each to a 10ohm resistor (to prevent current from following back into amp) before merging into speaker + terminal
Headphone jack GND to speaker - terminal

[Cookiemonster]

I can try to draw a nice schematic for you, but its better to use existing drawings


This is the way it should be done, in my opinion. with the minor change that you use a DAC circuit form PWM i suppose?

[BadBert]

Hmm... damn...

i'll have to re-wire my audio stuff then...

i also see the amp is just for the speaker in this image? Not for the headphone?

I would think you want to both boost the audio on the speaker AND the headphones?

I now have it :
USB DAC -> AMP -> POT (after market) -> gb jack and speaker

In the original wermy video's, he also boosts the headphone jack, but now that i look back.... he goes from the pot, to the amp
so... i'll change the position of the pot.

[RxBrad]

USB complicates this discussion a bit. By design, the USB sound dongles are amplified enough to drive headphones. The PWM circuit coming from the GPIOs isn't, I believe.

With the PWM circuit, I tried moving the pot between the PWM and the amp, but it was utterly unlistenable. 50% static & buzzing / 50% actual sounds I wanted to hear.

I already know that my original wiring order had terrific sound quality. Also, PWM has its own "potentiometer" of a sort: software volume control. So, I think I'm just going to set the volume by software so it's at the maximum volume I'd ever want to listen to it when the pot is turned about 95% of the way up. Then, I'd expect that this would be roughly the same current going into the pot as what comes from the USB sound dongle. At least I'd think this is the case.