My tiny single sided LM3886 PCB layout. :) - Page 6 - diyAudio
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Old 15th July 2005, 08:27 PM   #51
cm961 is offline cm961  Canada
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Yes I've made a ton of boards now your (g's) method. I even tried to put the component side on after I'd drilled it. But I got some bad news, the scale is slightly off! I'm not sure whether its the component mask or the copper, but the chip fits in the copper just fine, no pins bent or anything, so I must have printed the component side wrong. Also I used just normal paper for the component side, and it actually worked, mostly. I just had it and wanted to try it. In the future I'll use the inkjet photo paper just like I did for the solder side.

I'm still having trouble getting the paper off (trouble = takes forever). Hot water did make it easier, but its still a pain. I think leaving it overnight is the ultimate solution but I'm too eagre. We need to find a chemical which will dissolve the paper quickly but not affect the toner or copper!

Thanks again for the design, I haven't soldered the components on yet but I have 20 perfect boards.

Pete
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Old 15th July 2005, 09:16 PM   #52
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I just double checked the PDF files, they are correct.

Make sure when you print the PDF you have page scaling turned set to none, otherwise they will not be correct.

I am glad it went well for you! Enjoy!
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Old 15th July 2005, 11:34 PM   #53
cm961 is offline cm961  Canada
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Yeah I may have had it scaled. Either way it's so close that I'll easily be able to make them work, so I'm not concerned.

The question is, what am I going to do with 20 boards. I'm planning/building a set of studio monitor speakers which will be two way bi-amped, so I need four for that. I intend to make the complete circuits (power supply, preamp, filters, power amps) all on one board but these boards will be great for prototyping. I may use the LM3875 for the tweeters though as I've heard it sounds slightly better.

Pete
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Old 16th July 2005, 04:07 AM   #54
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Quote:
Originally posted by cm961
Yeah I may have had it scaled. Either way it's so close that I'll easily be able to make them work, so I'm not concerned.

The question is, what am I going to do with 20 boards. I'm planning/building a set of studio monitor speakers which will be two way bi-amped, so I need four for that. I intend to make the complete circuits (power supply, preamp, filters, power amps) all on one board but these boards will be great for prototyping. I may use the LM3875 for the tweeters though as I've heard it sounds slightly better.

Pete

When you get that board designed I would like to see it.
Maybe I could help?
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Old 16th July 2005, 02:46 PM   #55
cm961 is offline cm961  Canada
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Sure.

The power amp is based on a 18-0-18 transformer (I think, something close to that). So whatever rails that gives me. Then I need a +15VDC and -15VDC for the preamp.

The preamp will consist of a buffer / attenuator, crossover, linkwitz transform (on the woofer only) and gain adjustment / attenuator on the tweeter.

The amps will be similar to the one you designed, only I'll likely use the LM3875 for the tweeter as I mentioned. I'm also thinking of using a ribbon tweeter. Not sure what to use for the woofer although I'm thinking both will need to be shielded.

Everything mounts to a plate which mounts to the back of the speaker. The exterior side of the plate gets a large heatsink.

There will likely be three knobs: volume, tweeter level, and linkwitz transform level (so that it can be reduced if near a wall or whatnot). There will also be a fuse on the line, and a power switch.


Pete
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Old 16th July 2005, 03:01 PM   #56
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From experience I can tell you in no uncertain terms that the LM3875 while a good and worthy chip has nothing over the LM3886 in any audio band, bass, mid or trebel. I am not sure where you are getting that. I spent the better part of a week testing that exact (triamplified speaker) scenario at the UT lab.

I would stick with te LM3886 though I am quite certain it will sound fabulous either way.
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Old 16th July 2005, 03:12 PM   #57
cm961 is offline cm961  Canada
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Hmmm thanks for the advice! I suppose I'll just use the LM3886 then. It simplifies the design a little.

Pete
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Old 19th July 2005, 07:57 AM   #58
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Hi Russ,

Very nice PCB. I've been trying to learn eagle but haven't produced anything yet.

By chance, I made a little GC very similiar to this one, except I used a t-net for the feedback network. It was just an exercise in making it as small as I could. It's gotten a little ugly after changing the resistors a few times. My conclusion was if you make it too small it is very difficult to experiment with. Once you have the design finalised then its OK.

thanks
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Old 19th July 2005, 12:30 PM   #59
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Default Smallness

Quote:
Originally posted by Greg Erskine
Hi Russ,

My conclusion was if you make it too small it is very difficult to experiment with. Once you have the design finalised then its OK.

thanks

The design is finalized here, it is really just the datasheet NI circuit. The funny thing is the "smallness" was never intentional, it just happens to be tiny. I designed it around the size caps I have. Really its not that small, and its easy to work with because everyting lies flat and flush.

Good luck with your design work.

Cheers!
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Old 26th May 2006, 05:22 AM   #60
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I know, this topic is old but - what values should be used for RZBL (The resistor) and CZBL (The capacitor)?
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