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Old 22nd August 2012, 08:28 AM   #161
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Quote:
Originally Posted by atupi View Post
DC offset: 2,5mv\-1,5mv
Very good values
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Old 22nd August 2012, 08:47 AM   #162
bcmbob is offline bcmbob  United States
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Another method - if you have two heat sinks - is applying automotive grinding compound on the surfaces and simply rubbing them together. Working through a couple grits will result in both parts being pretty close. You should be able to buy a couple small tubes of different grits from a local hardware or auto parts store. If you care to, this method will get you all the way to a mirror finish.
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Old 22nd August 2012, 09:51 AM   #163
atupi is offline atupi  Romania
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My heatsink looks very similar to the one from picture above.

Does your Lm317 CCS are running hot. I cant stay too much with my finger on them.
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Old 22nd August 2012, 10:17 AM   #164
bcmbob is offline bcmbob  United States
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If you have similar heat sink and the surface looks the same, I would look for a gap at the top or bottom caused by an incorrect drilling angle for the screw. On the V1.2/3 boards the edge of the PCB prevented full contact of the chip. Dario made adjustments to hopefully prevent that, but if the LM3886 wasn't installed properly there may be an opening. Did you raise the LM3886 off the board before you soldered tha leads? Using a laser thermometer the 3886 and 317 are within 4 degrees ~ 78 - 81 F
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Old 22nd August 2012, 10:26 AM   #165
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Does your Lm317 CCS are running hot. I cant stay too much with my finger on them.
LM317s runs hot (54C at 30 room temperature) but an heatsink it's not required, according datasheet.

It would not harm either to use one, the same code specified for R3 can be used.
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Old 22nd August 2012, 10:30 AM   #166
bcmbob is offline bcmbob  United States
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It's too early in the morning here, but later I will crank up the volume and measure temps again.
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Old 22nd August 2012, 10:56 AM   #167
bcmbob is offline bcmbob  United States
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While we are on the subject, If you are not using a part of the chassis as a heat sink, it is helpful to: 1. attach the standoffs you will be using. 2. Place a small shim/spacer under the heat sink before you locate the drill hole. That will allow clearance and a bit of "swing" on the heat sink that can compensate for improper alignment.

And again, use a spacer between the bottom of the LM3886 and the PCB. Dario noted earlier that he used a layout on the holes for that chip that are larger and as a result will let it drop to flush. Don't let that happen.

P.S. I'm assuming this is obvious but I will repeat it non the less. The attachment screw/bolt must be tight AS you solder the pins. Trusting you lineup measurements will probably cause difficulties later. A small dot of solder on the top of the boars at two locations will stabilize the chip enough to allow you to turn it over and complete the soldering on the bottom.
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Old 22nd August 2012, 02:46 PM   #168
bcmbob is offline bcmbob  United States
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Now that the neighbors are up, after 30 minutes of loud pipe organ and big band jazz I'm getting 124 - 127 on the Lm3886 and 89 - 92 on the 317s. The room temp is 70 F.

I did discover that the outside corners of the heat sinks have a 10 degree spread between the two amps - so I need to do some work on my contact surfaces also.
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Old 22nd August 2012, 02:52 PM   #169
AndrewT is offline AndrewT  Scotland
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A 30C (54F) rise for Tc is good. Not excellent.
But, is that actually Tc or is that the surface of the plastic packaging on the chip which could be at a very different temperature from the chipamp?
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Old 22nd August 2012, 03:05 PM   #170
squalor is offline squalor  United States
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O.T. Got a reply from Uriah and he is feeling much better and is making good progress in his situation. Let's keep him in our thoughts and prayers.
Yea, he's a good guy; I hope he beats this and gets well soon.
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