Low cost Power Amp PCB from the net (LM3886) - what do you think of the schematic?

[AndrewT]

Move the cuts to the other end of the bridges next to the copper surround.
You are less likely to damage the Pad.

[marce]

Andrew T explain what you mean in your self opinionated reply in past 10.
I would suggest you do some re-search in PCb design over the last 20 odd years outside of the little world of audio design forums.
Mt research is based on 25+ years of PCB design and reseach on PCBs of working on designs from electron microscopes, to daresbury and cern to doing military design work, to consumer white good etc etc.
So instead of wroting balderdash, explain why you think it is.

[bidibidi]

Originally Posted by discrete

....here are 2000

Just saw your post. Thanks!
I was probably writing my reply, when you post yours.

Originally Posted by AndrewT

Move the cuts to the other end of the bridges next to the copper surround.
You are less likely to damage the Pad.

Ok. I am cutting it tonight.

[AndrewT]

20years or 25years neither qualifies as historical.
When did point to point wiring exist?
When did PCB first start being adopted?
When did Digital start?
When did analogue ground planes start?
When did digital ground planes start?

Your post is about modern, not historical.

Go back and read what you said in post8 from which I extracted the quote.

[marce]

25 years is suprisingly long in electronics, re moores law and the cahnges we have seen over that time span. The change from throught hole to SMD, lead free, component size reduction etc etc, the move from taped up artworks to CAD generated data, the rise and fall of Gerber photoplotters, the decreasew in voltages the increase in clock speeds. My post is about designs that I did years ago as well as designs I am doing now.
All my designs have had to pass EMC, as well as working, so are tested to the nth degree, so we learn in PCB design land as we go along, and modify our practices with the time.

http://www.hottconsultants.com/techt...gnd-plane.html
http://www.elmac.co.uk/pdfs/Lord_of_the_board.pdf
An intuitive, practical approach to mixed-signal grounding
http://focus.ti.com/lit/an/sbaa052/sbaa052.pdf
http://focus.ti.com/lit/ml/slyp167/slyp167.pdf
http://www.ieee.org.uk/docs/emc1206a.pdf
http://www.icd.com.au/articles/Split...s_AN2010_6.pdf
http://www.analog.com/static/importe...0Grounding.pdf
http://www.analog.com/static/importe...als/MT-031.pdf

Laid out the digital and ADC boards for Syntel for this project,
(unfortenatly Syntel is now defunct) all multi layer with ground planes.
http://accelconf.web.cern.ch/accelco...C1994_1551.PDF
http://accelconf.web.cern.ch/accelco...C1994_2333.PDF

[bidibidi]

I used a cutter to cut the bridges. It was not as easy as first thought. The bridges are tiny. Cutting them is closer to a surgical operation than general DIY.

The lower C4 pad is now separated from the power ground, confirmed by the Ohm-meter. I checked that the bottom trace is electrically connected to the top pad.

What is next?

Regards,

[AndrewT]

relabel the schematic.
Change all the Signal Grounds to say SG/SigRetn. R5 & C4 connect to SG
Change all the Power Grounds to say PG/PGnd.
Not shown on the PCB, but add a notional Main Audio Ground (Star) labeled MAG or Star *.
This is where the speaker return connects, not the PG.

Add the missing RF filter to the input.
Add the missing Zobel/Thiele Network to the output connected to PG.
Update the power pin decoupling to match National's recommendation.

Build up your PCB keeping those three grounds separate.

[bidibidi]

Originally Posted by AndrewT

relabel the schematic.
Change all the Signal Grounds to say SG/SigRetn. R5 & C4 connect to SG
Change all the Power Grounds to say PG/PGnd.
Not shown on the PCB, but add a notional Main Audio Ground (Star) labeled MAG or Star *.
This is where the speaker return connects, not the PG.

Beginners like me have hard times understanding simple sentences like yours.
I hope that I relabeled correctly.

Originally Posted by AndrewT

Add the missing RF filter to the input.

?
How should the missing RF filter look like?

Originally Posted by AndrewT

Add the missing Zobel/Thiele Network to the output connected to PG.

Not sure about the Thiele network either. I understand that it reduces RF from and to the amp, but I am not sure about component values and configuration.

Originally Posted by AndrewT

Update the power pin decoupling to match National's recommendation.

?
Do not understand.

Originally Posted by AndrewT

Build up your PCB keeping those three grounds separate.

?
Where should the MAG be?


Regards,

[AndrewT]

Nearly there.
Read National's datasheet for supply rail (power pin) decoupling.

Read National's datasheet for details of output Zobel. The 1r0 resistor comes after the Zobel R+C

The Speaker Return must be connected to MAG not PG.

When you have that, there is yet more to come.

[bidibidi]

Originally Posted by AndrewT

Read National's datasheet for supply rail (power pin) decoupling.

Do not understand what the sentence means. It is regrettable that my degree is not in electronics.
Decoupling the supply rail does not evoke anything concrete in my mind.
Sorry, I will have to ask for help. Newbie here.

Originally Posted by AndrewT

Read National's datasheet for details of output Zobel. The 1r0 resistor comes after the Zobel R+C.

One day, I may need to get a formal training in electronics. For now, I have to ask for some guidance. I could not find the work Zobel in the 3886 datasheet. I hope that the new corrected schematic is ok now.

Originally Posted by AndrewT

When you have that, there is yet more to come.

MORE TO COME?
...
I thought we were almost there...


hope not much more.

Regards,