An open source layout for LM3886?

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#221
viki_v2 said:
Has anyone built this amp.
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I built it for a friend 18 months ago, I think it is excellent.

I have the Gerber files available on my hobby website (with links to this page) and they have been accessed over 1000 times, so I would say there are probably a fair few completed amps out there. Very few people come to this page asking for help which could suggest they haven't had any real problems with it.

It's relatively cheap to build, why not just send the files off and give it a go?
 
#224
00940 said:
AWG18 should fit without problem, AWG16 will be too tight. The drill hole is a 1.3mm one.
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Thanks for confirming the drill size. My digital calipers aren't good enough (and probably aren't the right tool) to check them since I get a reading of 1.2x mm.

I was considering whether to solder wires directly to the board or use a terminal block. At the end of the day I suppose anything other than soldering (at least for my application) would just be a waste of time and money, as 18 AWG is more than enough for how much power I need out of these.
 
#228
viki_v2 said:
Has anyone built this amp.
Click to expand...

I just realised I only posted my build to the main gallery thread & never actually contributed back to this thread. I finally finished it back in May this year, after starting in 2018.

It is a 3 channel build for a 2.1 setup, with two of the boards bridged via a Vigortronix VTX-101-007 audio transformer. There is a lot of empty space in the enclosure because I originally intended to house an active crossover & its power supply in the same enclosure, but in the end I stuck with my separate dbx crossover. I know my hand wound coils are bad, but I have to leave myself something to improve on next time.

I also built a 3U rack from some cheap plywood.

I am very happy with the results. I used my last gainclone for 8+ years & I now intend to use this one for 8+ more.
 

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#229
Are these files good to go to the forge?

00940 said:
Well, there are two issues here. One is how things are joined and the impact of common tracks' impedance. No objection on that, the feedback cap has to go to the input gndplane. The other thing, less clear, is about loop area and radiations pickup. Groundplanes are relevant to both issues as provide a low impedance connection but also allow to reduce some loops.

So, here's an attempt to satisfy all the compromises. Yeah, I wish... As before, the zip is for the eagle files.

The feedback cap now returns to the input gnd. The feedback resistor going to gnd is over the split between the signal and the power gndplanes. If you consider the loop mentioned in the post above, it's quite tight.

The two gndplanes are joined near the output connectors by a resistor. It can be jumpered in case of a mono amp.

Better now ?
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First of all, many thanks... I've been looking for a project like this for so long...
I'm planning on printing the PCB's and make (another) an amp for myself
So... I have some questions:
Are these gerber the final version? Anything I should be worried about? Do you have a BOM's list? (found them, thanks)I don't want to mess it up
And thank you so much for all that work, it looks amazing by the way 😀
 
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#231
When the files are uploaded to JLCPCB, only the amp board autofills in the dimensions of the board and allows previewing of the PCB.

The Power supply board and Protect board do not auto fill the board size and you cannot preview the PCB with their online Gerber viewer.

Any ideas why?
 
#233
DaveFred said:
The Power supply board and Protect board do not auto fill the board size and you cannot preview the PCB with their online Gerber viewer.

Any ideas why?
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It might very well be that I messed up and never uploaded the gerbers but only the Eagle files :boggled:

They haven't been very popular to start with so it's never been pointed out. I'll reinstall Eagle and generate gerbers.

My apologies 😱
 
#234
Gerbers

Thanks for this project, it looks like just what I've been looking for!

What version of Eagle are you running?

I tried to open the files, but my (quite old and in need of update) version of Eagle errored on them.

When you get a chance to do the PS and protection gerbers, it would be nice to have them.

Many thanks!

Adam
 
#235
I re-attached all the files to this post.

The files open without problem with Eagle 8.7.1
 

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#237
I just want to thank you for making this design public and available for everyone. This is really helpful to me as someone who is just getting into playing around with chipamps, and I think the difference between 0.001% and 0.000000001% THD is mostly academic and completely inaudible to human ears. So this amp design more than delivers on performance as compared to some of the other, composite LM3886 designs I've seen on this forum. Thank you so much for this design!
 
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#238
Changing Gain

Hi Guys,

A quick question.
I am about to build another pair of these but I want much lower gain this time round. Something like a gain of 13.

R5 is easy, I would simply change to 12k.

However I am uncertain what to do with the filter of R7 and C5.

Do I need to change R7 from 22k to 12k as well?
 
#239
DaveFred said:
The Power supply board and Protect board do not auto fill the board size and you cannot preview the PCB with their online Gerber viewer.

Any ideas why?
Click to expand...

That sort of stuff often happens if the FAB layer is missing. The FABrication drawing is basically the board outline and through-hole locations.

For a two-layer board with top silk screen, you need the following files:
  • Top copper
  • Bottom copper
  • Top solder mask
  • Bottom solder mask
  • Top silk screen
  • Echelon (X,Y) file for the through-holes
  • Fabrication drawing

Your layout tool should be able to produce these in Gerber 2.74 format.

Tom
 
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