Lme49830

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Segran

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Joined 2008
It looks OK, but I wouldn't use a ground plane for an audio amplifier PCB. If I did, I would use it for Signal GND, not Power GND.

To avoid oscilations I suggest you put the Gate resistors for the MOSFET's directly on the Gate's, either on the separate PCB for the output stage or directly P2P.
 
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AndrewT

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Joined 2004
the decoupling caps on opamps, chipamps and amplifiers are there to reduce glitches & spikes in the power supply when currents turn on or off suddenly.
These glitches and spikes are not clean. They must never be taken through a clean return or shared with another clean signal.
 
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Segran

Member
Joined 2008
Hi Nick,

your changes fixes noise (spikes) coming in from GND. Personally I would get rid of the power plane you have on the top layer as well, since it's connected to PGND. I have seen spikes entering the op amps through capacitive coupling from noisy power ground planes.
 
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Segran

Member
Joined 2008
Sorry Nick, Per-Anders is right! I read the Pin Descriptions in the Datasheet which says just "Device Ground" and have jumped to a false conclusion. I stand corrected....:ashamed:

I wish somebody had pointed out that mistake in my own PCB layouts I have posted here. :bawling: I will have to re-do the layouts - again....

However, in Figure 4 on page 14, NS have connected the bypass cap's for the LME49830 to Signal GND while the output stage cap's are connected to PWR GND. I don't see the reason for this, so until I get a rationale for this I still believe that all bypass cap's connected to the power rails should always got to PWR GND. :dodgy:

Re. power planes, I come from a digital world where power planes are frequently and succesfully used (also by me...). I haven't been that succesful when using power planes in my DIY analog project. Based on my experience I have moved to a more stringent Star methodology also on the PCB's and thereby reduced noise levels significantly.

But as I said in one of my first replies - there are may far more knowledgeable posters than me on this great Forum! I'm in a constant learning mode myself.
 
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AndrewT

R.I.P.
Joined 2004
Hi,
if fig2 is telling the whole story, then interpret GND as Power Ground.

A dirty mute signal will contaminate the Signal Ground and we don't need that extra complication.
Page11 goes further, the mute current must be very clean if one wants to avoid Signal Ground deterioration.
 
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