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Old 13th August 2010, 12:53 PM   #531
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Default Updated Tiny Tutorial and BOM

Attached the updated tutorial and BOM.

Note that the BOM is semi-final with final recommendations as per my post on the other thread
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File Type: zip My_Ref Ultimate Rev C.zip (716.5 KB, 73 views)
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Old 13th August 2010, 04:27 PM   #532
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Bill,

Excellent point about insulated vs non-insulated chips.

Why would one need high shear strength for a bolt holding a tiny chip against a heatsink? This amp is not going for a ride in a rocket! If this fastener is ever in shear, you've got bigger problems than the bolt material. Actually, I think the lower tensile strength and soft "feel" and flexibility of the nylon bolt is an advantage here. With the insulating pad behind the chip, you don't want to tighten the fastener so much that you tilt the chip or crack its case or cut the pad. Most likely, the threads will strip or the bolt will break before any of that happens. It doesn't conduct heat, but it is more thermally stable. It is also non-magnetic, if you care about that sort of thing.

Silly thing to argue about, but I think nylon is perfectly suited to this task, especially for people who don't have tiny torque wrenches or a lot of experience attaching chips.

Of course, the supplied shoulder washer also works well, but a nylon bolt is nearly foolproof.

Peace,
Tom E
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Old 13th August 2010, 05:30 PM   #533
troystg is offline troystg  United States
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Just to confuse things... :-)

I use the uninsulated package (with insulator) clamped down with a cross bar to hold it on the heat sink. That gives me very solid mounting and additional heat dissipation from the front (not that it's needed).
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Old 13th August 2010, 06:27 PM   #534
Bill_P is offline Bill_P  United States
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Regarding plastic or nylon mounting hardware, here is a quote from the Caddock application note AEN-0101:

Plastic mounting hardware that softens or creeps at
high operating temperatures must be avoided.

That's aside from the low clamping force achievable with non-metal screws. The Caddock note is highly recommended reading regarding mounting the LM3886 as it explains all the interface characteristics. They also recommend Belleville washers to maintain consistent clamping force. They were not supplied with the kit but I used them in my build. Caddock supplies resistors in packages similar to the ones power semiconductors come in so the application note is entirely relevant to the LM3886, MOSFETs and other power devices.

I don't really intend for this to be an argument, just stating my own preferences and supporting what I said with a component manufacturer's application note.
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Old 14th August 2010, 01:52 PM   #535
vlad712 is offline vlad712  Moldova
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Hi friends

Last evening I was happy to hear the music from one channel.
As you knows I've successfully fried my LM3886 by connected it to the heatsink without insulating. Yesterday I've replaced both LM3886 and LM318H. Relay didn't click. Then I shortened R14 by isolated tweezers - relay clicks on and music flows - I was very shocked - it was soft and detailed. When I put my tweezers off R14 relay clicks off.
Changing R14 to 195R and then to 130R - didn't help. The relay clicks only when shorting R14.

What should I do next: changing BC639 or, maybe to do one more missing step: connecting the transformer and the board to the ground?

I've connected Nuvotem transformer with dual secondaries directly to the board: Red-White to one channel and Yellow-Orange to another without central tapping, and didn't ground the case. Could it be the reason for relay non-clicking?

Vladimir
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Old 14th August 2010, 02:10 PM   #536
Bill_P is offline Bill_P  United States
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Quote:
Originally Posted by vlad712 View Post
I've connected Nuvotem transformer with dual secondaries directly to the board: Red-White to one channel and Yellow-Orange to another without central tapping, and didn't ground the case. Could it be the reason for relay non-clicking?

Vladimir
It appears you do not have the transformer connected correctly. Is there a web site to look up Nuvotem? Maybe a diagram of how you connected the transformer and some photos of your wiring would help to tell what is wrong.
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Old 14th August 2010, 02:18 PM   #537
vlad712 is offline vlad712  Moldova
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Hi Bill
the wires goes directly from transformer to the boards
Attached Images
File Type: jpg 0500P1-2-025-pinout.jpg (9.2 KB, 284 views)
File Type: jpg P1060527_small.jpg (204.6 KB, 305 views)
File Type: jpg power_small.jpg (104.0 KB, 279 views)

Last edited by vlad712; 14th August 2010 at 02:20 PM. Reason: adding some detailes
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Old 14th August 2010, 02:25 PM   #538
Bill_P is offline Bill_P  United States
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Connect black and yellow together and then to power ground on both boards. Connect the red wire to AC1 on both boards. Connect the orange wire to AC2 on both boards. Power on the amplifier and see if it works as it should.
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Old 14th August 2010, 03:42 PM   #539
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Quote:
Originally Posted by Bill_P View Post
Connect black and yellow together and then to power ground on both boards. Connect the red wire to AC1 on both boards. Connect the orange wire to AC2 on both boards.
Wire cables as Bill told you then connect PGND of each board to safety ground and make a Y like this one:
Attached Images
File Type: jpg SingleTransormer.jpg (100.2 KB, 268 views)
File Type: png PGND.png (23.1 KB, 224 views)
File Type: jpg Wiring.jpg (157.6 KB, 110 views)
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Last edited by ClaveFremen; 14th August 2010 at 03:51 PM.
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Old 14th August 2010, 04:33 PM   #540
troystg is offline troystg  United States
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Quote:
Originally Posted by vlad712 View Post
Hi Bill
the wires goes directly from transformer to the boards
I hope you are not using that speaker wire for 240VAC mains cable.. I doubt that cable insulation was rated for that voltage. Also the hole in the chassis will chafe that insulation in no time. Better off using one of the Neutrik power-conn connectors in that tight spot.

Also the transformer is definitely wired incorrectly as they stated.
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Last edited by troystg; 14th August 2010 at 04:35 PM.
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