Hi Everyone,

I was looking at this schematic from theorycircuit.com and was curious what the purpose of 1 ohm resistor (R4) in the schematic is used for?

I think it's used to connected the Signal Ground and Power Ground together in a Star Grounding formation. Most of the references I've read do this using a 0 ohm resistor. Is there a reason for using 1 ohm instead or is R4 there for a different purpose?

Thanks for the help!

 

The datasheet for the PAM8403 says, "Not Recommended For New Designs, use PAM8406" so maybe it has a problem.

 

It's not present in the datasheet for the PAM8403 or replacement chip, PAM8406. It looks more the designer added the component, and I was curious of why they chose to do so.

My thought was either it's used to combine the Signal/Analog Ground to the Power Ground, but like I said either usually I've seen the two different grounds linked together using a zero ohm resistor. So I wasn't sure if this was the purpose or is it being used as a filter of some sort since it's a non-zero value?

 

It's part of a analog power filter hack for the input stages on the chip. Looks like maybe there was a power stage noise problem that is helped a bit by diverting the class-D digital pulse noise current PVDD/PGND loop out of the input VDD/GND loop.
https://www.arrow.com/en/research-a...nciples-of-grounding-for-mixed-signal-designs

 

Looks to me to be a current-sense resistor, for feedback to prevent excessive output current. But the schematic wrongly identifies the right-hand node of R4 as GND: it should be PGND.
If pins 2 and 5 of J4 are shorted as shown, then the current-sense purpose of R4 is defeated.

 

There are to GND pins at the amplifier one fr input stage one 2 others for the power stage. This resistor is some kind of isolation between input stage and power stage, not much current should be flowing through R4.

 

It looks like an effort to isolate that external controls section connected to J4 from the power ground, It is undoubtedly there to compensate for something on that module that is not quite right. Designers do overlook things sometimes, and IC revisions are expensive and delay time to market. So they release a patch like this instead.