BPA200 / Stereo Bi-wire PCB V1

[bm0rg]

Hi all,

Just finished laying out this board. Its based on National Semiconductors bridge/parrallel amplifier schematic (figure 13) from the document http://www.national.com/an/AN/AN-1192.pdf.

Id very much like some feed back and people to check I havent made any mistakes before I send it to be made.

Parts match that on page 18 of the AN-1192 document

Configurations options of the board:

BPA 200 with servos
BPA 200 without servos
4 single LM3886 (stereo bi-wire) 4 seperate ins and outs

Attached should be a PDF of the top + bottom + silk

Thanks for looking

[bm0rg]

Top layer and silk.

[bm0rg]

Bottom layer and silk

[pacificblue]

Looks, as if you had skipped a bunch of capacitors. There only seems to be one of the eight 100 nF decoupling caps (Cby2) on the board. The missing ones can still be soldered directly to the IC pins, but where do the 470 µF (Cby5) go? The two 3300 µF capacitors on board are not replacing the eight 10000 µF capacitors recommended off board in the application note, are they?

Four separate muting circuits can lead to strange behaviour at the speaker terminals. The capacitor tolerances will lead to unsynchronized activation of the four amplifier channels. One Rm/Cm combination that acts on all channels would be better.

There seem to be three missing connections. RF4 to its corresponding output, RD1 to CD1 and Rb3 to CB2.

[sasmit]

isolation for the ground polygon is too small, you need to increase the isolation(clearance between components not connected to ground and ground plane ). PCB maker might not be able to work with this much tolerance.
IMHO ground plane type design is not preferred especially for high power amp designs...national mentions the same on their application note on LM4702 based power amp design.

[bm0rg]

Thanks for the feedback pacificblue and sasmit! Much appreciated.

I have so far corrected:

The 7 missing CBY2

Removed 3 of the muting circuits and join U1,U2,U3,U4 to a single muting circuit I guess the values will now be quiet different? Each chip needs to draw 0.5 mA so all 4 together will 2mA right?

Sorted the three missing connections.


Having done that this just leaves the 470uf caps and ground plane.

These two issues require a major redesign i.e. a bigger board to accommodate 8 470uf (12mm in diameter the smallest I could find for 50V) in there various places close the IC would be best I guess?

The 3300uf were just there as extra to make up for the 2 73800uf supplies in my 2 BA100 amps. I was going to use one per channel for the BPA200 this should be enough. Do I need the extra 3300uF? I guess 8 470uF close to the pins would be better than 2 3300uF?

Thanks again guys for the help.

Attached a pic of the current supplies for those interested

[pacificblue]

Originally posted by bm0rg
Each chip needs to draw 0.5 mA so all 4 together will 2mA right?

Right.

Originally posted by bm0rg
I guess 8 470uF close to the pins would be better than 2 3300uF?

Absolutely.

[bm0rg]

Hi,

Ok here is V2 with the corrections. The layout is a little different and some how ended up being a little smaller.

CBY5 and CBY2 are all as close to the pins as I could get them.

For the muting circuit if I have a power supply of +/- 36 v dc which if I calculated correctly Rm should equal 16700 ohms so I guess a 16k or 15k resistor?

Cm I believe softens to mute on/off. 100uF ok?

Thanks every one for the help so far.

[bm0rg]

And the top layer

[bm0rg]

And the bottom