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Old 11th October 2011, 09:24 PM   #1
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Default Yet another LM3886 PCB post!

Hello,

I appologise if I have totally missed threads about this, however I have searched but to no avail!

I am trying to sort out a PCB layout for and LM3886, I've looked at various pcb layouts on the net, however I am getting somewhat confused

I was taking the circuit from the LM3886 datasheet, this shows 4 caps, namely:

Cm
Cs
Cs
Ci

I have seen designs with 6 caps, where have these come from!

All I want to do is sort out a high end layout, then etch it myself!

So is the standard schematic from the datasheet ok, or a bit pants to use as the cct?

Many thanks, once again appologies if I've annoyed anyone!
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Old 11th October 2011, 09:31 PM   #2
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The datasheet schematic is fine, and a good start. You can always tweak later if you want as you'll already have all the expensive stuff like case, heatsinks and PSU.
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Old 11th October 2011, 09:53 PM   #3
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Thanks for the response.

Right so decoupling caps on the power supply, I assume should be 4400uF or something similar,.

Feedback cap, 22uf (from datasheet)

However what value to use for the mute cap?

Once again, many thanks!
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Old 11th October 2011, 10:28 PM   #4
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Yup, sounds reasonable, and the calcs are on the datasheet, IIRC, I used about 10uf.
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Old 12th October 2011, 06:33 AM   #5
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Many thanks, I'll get drawing!
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Old 12th October 2011, 10:07 AM   #6
AndrewT is online now AndrewT  Scotland
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Each Cs is a pair of caps.
RF attenuation filter cap.
Zobel output load.
DC blocking cap on input.
DC blocking cap on NFB lower leg.
Muting cap is optional.
Input RCA RF filter cap is optional.

That's 8 to 10 caps and does not include the PSU.
I have missed one there should be 11 caps.

Read the sections about what National refer to as "optional components". For a reliable and consistent build/performance all these "optional components" are required.
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Old 12th October 2011, 11:30 AM   #7
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Thanks AndrewT, I will get reading, prior to drawing!
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Old 13th October 2011, 07:40 AM   #8
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Ok,

I've read the datasheet and am looking at making some additions.
I've also started to read up about Zorbel, however I can't seem to find any info on it relating to the amp, i.e (sorry for being really basic) the configuration for this app!

I've tried looking for a thread on the subject, however to no avail!
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Old 13th October 2011, 08:24 AM   #9
AndrewT is online now AndrewT  Scotland
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insert Zobel and/or 3886 in the search and you will find hundreds of thread discussing the subject.
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Old 15th October 2011, 06:18 PM   #10
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All sorted!(wrt Zorbel etc).

PCB should be finished in next couple of days.

Only thing is that I've gone for SS board, so if people want to it could be made at home.
Has anyone done a comparrision between 2 layer and ss boards?

I assume that 2 layers may sound better hence why they are used?
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