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Old 19th August 2016, 03:58 AM   #1
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Default Neurochrome LM3886DR Build

Hey guys,

a few months ago now after a failed attempt at buying a chipamp.com kit, Tom mentioned he would be making the LM3886DR Kits, so I immediately put my name down for the first one. It turned up quite a while ago, however I've had a busy few months and haven't had a chance to start putting it together until now.

Cutting the box open, everything was individually bagged and labelled from Mouser - so much more convenient than trying to figure out a handful of components. Thanks to Tom for helping me out with getting all components along with my boards.

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Printed off the design documentation - super comprehensive and walks you through every step of the build (including about as much information on the chip as you're going to find anywhere). Easy enough to follow that providing you can solder, it's pretty hard to go wrong building this kit.

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Started populating the boards with resistors. Again, having everything bagged and tagged makes this process super easy.

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Power resistors in. Left 5mm gap for airflow around the resistors.

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All caps in.

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Connectors and inductor in.

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LM3886 in (easy to solder, was annoying trying to lift it a pinch off the board for clearance - more due to my fat hands than any issues with the kit).

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Chip attached to temporary heatsink for testing. Definitely overkill, but I had it floating around. Checked DC offset at the output - 3.5mv; perfect.

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Attached to a test speaker and lab power supply. At the start of testing I was hearing some terrible things - the cone flapping around, continual cracks and pops, etc. Figuring I had something wrong I went through and verified all components with no success - turns out I had a faulty signal generator! Switched over to another one and it was perfect.

-----TBC-----
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Old 19th August 2016, 04:03 AM   #2
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Nice. How many channels?
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Old 19th August 2016, 04:04 AM   #3
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Had a few other people in the workshop so tried to keep test volumes low - 400Hz sine wave input.

20160818_163321 (Custom).jpg

And speaker voltage. Near enough to +26db gain

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Unfortunately I didn't have time to put it on a scope, but I'll try for that over the weekend.


Next job: building the second board and starting on the power side of things.
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Old 19th August 2016, 05:47 AM   #4
AlexQS is offline AlexQS  United States
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Very cool. I too like the convenience of all the parts bagged individually from mouser. I've soldered together 9 of Toms boards, 3 THAT Line Drivers, 4 Mod86, and 2 Power86. Agreed that the step by step instruction is the best out there.

Tip for you. When I open the box from mouser, I turn to the page in the instructions that has all the parts listed. I match up the part number from mouser, then look at the list and write the corosponding board location on each bag, like C1, C2, R1, etc. For me, this step takes a good 30 minutes when you have parts for 4 Mod86 and a Power86, but once it's out of the way, I can put them in order, and stack all the mouser bags like index cards in a shoebox. They're all in order and you just pull the bag in front, quickly verify with Tims instructions correct part and placement on board, solder in place, on to the next.

Any who, congrats on your build. I'm glad you're having lots of success.
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Old 19th August 2016, 06:35 AM   #5
Spuds is offline Spuds  South Africa
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Very nice, had my eye on building one of these.
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Old 20th August 2016, 06:57 AM   #6
tomchr is offline tomchr  Canada
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Very cool! Thank you for starting this build thread and sharing your build experience. It's always fun to watch my products being built and put into service.

Tom
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Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 20th August 2016, 11:52 AM   #7
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#2 built and on the test bench. Again, pretty much 26db gain on the dot. You can see the poor cone having a fit with 50Hz haha.

20160820_145948 (Custom).jpg

Scope set up with input and output signals. 500mv/div on input, 10v/div on output - perfectly lie on top of each other (outputtinga bit under 50w here, if I remember how to math properly).

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Both boards side by side.

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Now, for the enclosure. Original plan was to put it into a 2RU enclosure, along with a pre-amp and some other bits and pieces (including a handful of modified eBay regulated PSU's that I've tested to 30V/5A output), but I'm thinking I might cast some aluminium and machine an enclosure on our CNC and go for a no-frills approach. We've recently got set up with a fairly decent foundry and have ~1000lbs of scrap aluminium, so it's a possibility! I've also got 500VA of recycled 24V transformers that I can use, along with a few toroids

Last edited by dreadnoughtstrength; 20th August 2016 at 11:55 AM.
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Old 20th August 2016, 12:17 PM   #8
zman01 is offline zman01  Bangladesh
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Nice work dreadnoughtstrength
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Old 20th August 2016, 04:55 PM   #9
AlexQS is offline AlexQS  United States
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Thanks for starting a his thread. I'm interested to follow it. Now that my system is mostly done, I need another project soon (I'm an addict!)

I think I'll build a LM3886DR as a gift for a family member.
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Old 20th August 2016, 05:34 PM   #10
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by dreadnoughtstrength View Post
#2 built and on the test bench. Again, pretty much 26db gain on the dot.
Cool! Nice work!

Quote:
Originally Posted by dreadnoughtstrength View Post
Scope set up with input and output signals. 500mv/div on input, 10v/div on output - perfectly lie on top of each other (outputtinga bit under 50w here, if I remember how to math properly).
Math is Pout = Vout^2/(2*Rload) with Vout in volt, peak.

or: Pout = Vout^2/Rload with Vout in volt, RMS.

Tom
__________________
Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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