| dfdye |
I just hooked up my newly completed LM3886 amp based on Linkwitz's circuit that I cranked out while waiting for the transisitors for my LM4702 to come in. Falling firmly under the "DUH!!!" category for most of the people on this board, I am quite frankly astounded that such nice sound can come from such an amazingly simple package. Right now the parts are flowing all over my workbench, but I will be sure to post some pics when I get it in the purty case I am building. So far it seems perfectly suited for life as my dedicated iPod/computer amp in my office.
Thanks to everybody for help the offered, whether you know you helped or not! :D |
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| dgaxeman |
| care to share on this ? building my first one. pcb schematics whatever? thanks |
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| dfdye |
The circuit I used was from
http://www.linkwitzlab.com/images/graphics/3886amp.gif
but the PCB was a custom one that I have attached. There are some things I don't like about the board that I figured out after I sent the boards into be manufactured. For example, CS+ and CS- are in the wrong spot (they should be right next to the chip and after the V+ and V- inputs) and I didn't ground the nonconnected pins (though I fixed that by wiring p2p on the boards when I put them together. Also, though I put a feedback resistor part on the board, I put the resistor directly across the chip pins.
The case isn't finished quite yet, but I will definitely post more pics when I have time to finish it up. It is, however, running strong in my workshop while I do stuff for work, and it sounds great. My Cheap-o Pioneers I bought in high school low these many years ago sound better than they have ever sounded (which is still pretty bad, but at least I have tunes in the shop :D) I have hooked them up to my North Creek CM-77's for more testing, and the sound is really nice. I know these aren't the best reference monitors, but my budget (and my wife) hasn't allowed me to get much better than that yet! :)
Here is the PCB, but I would recommend that a few modifications be made if anyone is interested in using the design. If anyone is interested, let me know and I will post a revision B. |
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| dfdye |
| This is a bad picture from my phone (which is the only digital camera I own :bawling: ), but it should get the point across. This (obviously) is the "mid/tweeter" version of the linkwitz circuit. The board obviously has places for electrolytic caps for the woofer version, but I haven't built a version of that amp yet with these boards. I have put together a p2p version of that circuit, though, and it has great low end response, but pretty terrible mid/treble. The bass response of the mid/tweet circuit isn't shabby, though, and I would strongly recommend this version if you are going to only build one amp per speaker. |
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| dfdye |
Here is the revision2 PCB layout if anyone is interested. I took off the feedback resistor assuming that it would be mounted to the chip pins. I also moved the bypass caps, shrank the board a little, and ran a better ground plane that actually connects the loose pins this time! :D
David |
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| Greg Erskine |
hi dfdye,
Nice work. We are watching. :D
Just a couple of points that I have read but not experimented with myself.
1. I don't think you need to worry about the NC pins. They can connect to anything or nothing. Connecting them to a ground plane does seem a nice thing to do though. Have you found it made a difference?
2. I noticed on the Linkwitz schematic that the mute resistor was a reasonably high value, limiting current. I have seem a few posts suggesting a higher current through the mute circuit is better.
regards |
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| jimbo1968 |
dfdye,
What was the price/quantity for your pcbs you had made?
Is single sided cheaper to get made? or is the advantage that you can etch it yourself?
I'd like to design a little 3886 board similar to that for my first pcb. What software did you use? Any chance I could have the files to get me started? :) |
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| dfdye |
| quote: | Originally posted by Greg Erskine
hi dfdye,
Nice work. We are watching. :D |
Thanks! This is definitely a learning experience. I have always relied on our electronics shop to do pcb stuff for me before I found this forum. I am amazed at how quickly you can pick it up! I am sure there is a ton I am doing wrong, but at least I am hafing fun messing things up! :D| quote: | | 1. I don't think you need to worry about the NC pins. |
I have never noticed an issue with NC pins in amps, but in the instrumentation I use in my lab (which is a few orders of magnitude more sensitive! :D) there can be issues. Good practice that I learned a long time ago was to tie all NC pins to ground if you can.| quote: | | 2. I noticed on the Linkwitz schematic that the mute resistor was a reasonably high value, limiting current. I have seem a few posts suggesting a higher current through the mute circuit is better. |
I haven't played with it, but thanks for the suggestion. So far, I don't have any complaints, but I will have to check that out! Easy swap. |
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| dfdye |
| quote: | Originally posted by jimbo1968
dfdye,
What was the price/quantity for your pcbs you had made? |
I ordered these boards from Olimex. They have a neat little deal where you can populate a eurocard with as many parts as will fit for one price. I got 2X of my LM4702 boards and 6X of my LM3886 boards for $36.30 shipped (and that included a goofy drill size)
The web page for the boards is: http://www.olimex.com/pcb/index.html
One thing you will have to deal with is Faxing to Bulgaria. That was interesting.| quote: | | Is single sided cheaper to get made? or is the advantage that you can etch it yourself? |
Both. For a board this simple you don't really need to run two sides.| quote: | | I'd like to design a little 3886 board similar to that for my first pcb. What software did you use? Any chance I could have the files to get me started? :) |
The software I used was Eagle, and you can use the free version and submit the files directily to Olimex. Do a quick google search for Eagle PCB and you should find the software. The tutorial will guide you through how to make the boards, so I would recommend you use this circuit as a test to learn the software.
Good Luck! |
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| jimbo1968 |
| Thanks, that's a great price on that link. |
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