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Old 14th August 2010, 04:33 PM   #541
Reality first!
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Default Updated Tutorial and BOM

Since I've made new images for the preceding post why not include them in the tutorial?
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File Type: zip My_Ref Ultimate Rev C.zip (744.7 KB, 84 views)
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Old 15th August 2010, 07:46 PM   #542
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I am familiar with that application note, and it is very informative. I read it while I was researching using the Caddock power resistor in this amplifier, which previously had not been attempted or even recommended. That's the kind of thinking and experimentation I'm trying to encourage here by suggesting something as simple as an alternative to the metal bolt and shoulder washer.

There is one important distinction between clamping a Caddock or similar device, and clamping the LM3886: one is in an insulated package and being clamped securely against bare metal; the other is susceptible to shorting and being clamped against a soft pad or fragile piece of mica. If one seeks electrical isolation, nylon is adequate for this task. If one seeks ultimate strength and mechanical stability, the shoulder washer and metal bolt will work better. I have used the same nylon bolt for several builds, and it is still successfully and securely clamping the chip tightly against its insulating pad and heatsink. Chances of shorting the LM3886 with a nylon bolt and insulating pad is zero. Chances of it failing mechanically, in everyday normal usage, are slim. Nylon 6-6, which is what most bolts are made of, is pretty stable even at elevated temps.

I like the washer idea, but there isn't much room for a washer on the mounting tab of the LM3886. One thing to be aware of when tightening whatever fastener you choose, is that too much pressure might allow the chip to tip and actually make worse contact. Another danger is not allowing the entire board to "pull up" to the heatsink as the fastener is tighted.

The clamping bar, such as what Troy uses, is even better for applying plenty of pressure equally, although more complicated and perhaps overkill for this app. Troy, what is the clamping bar made of?

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Old 15th August 2010, 08:08 PM   #543
troystg is offline troystg  United States
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Quote:
Originally Posted by madisonears View Post
.......Troy, what is the clamping bar made of?.....

Peace,
Tom E
I use Aluminum. If mounting one chip I use 1/2" wide bar and bolt it on each side of the chip. Sometimes I will put two LM3886 chips "mounting tab to mounting tab" and use one bolt between them with 3/4" Aluminum.

Works well but is generally overkill.. :-)
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Old 16th August 2010, 06:56 AM   #544
vlad712 is offline vlad712  Moldova
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Default my amp raised !!!

Thanks to Bill_P and Dario my RevC has successfully entered into acquaintance with my music collection.
I've wired the trans as advised and all goes as it should. +1 working RevC on planet.
I've also to state all parts in my kit works Ok (not concerning the chips which I fried due my personal ignorance).

Troy, I did connected GaleXL315 speaker cable as mains wire. Due to its thickness and thick silicone isolation I decided to try it as mains leads. It worked ok for about 2 weeks with my old amp.
Do You think it's not a good idea to use it this way and one day it could cause problems?

About grounding - if I have not safety ground in my flat, to what point on the board should I connect the case?
I can listen the hum when touching the case by hand, and woofer booms when switching the amp on.

Vladimir

Last edited by vlad712; 16th August 2010 at 07:19 AM. Reason: adding the question and details
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Old 16th August 2010, 05:17 PM   #545
troystg is offline troystg  United States
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Quote:
Originally Posted by vlad712 View Post
......

Troy, I did connected GaleXL315 speaker cable as mains wire. Due to its thickness and thick silicone isolation I decided to try it as mains leads. It worked ok for about 2 weeks with my old amp.
Do You think it's not a good idea to use it this way and one day it could cause problems?.............

Vladimir

Again my suggestion is a neutrik power-con connector or an IEC mains connector.

At the very least a mains rated power cord hard fixed to the chassis with a gromet / fastener system.
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Old 16th August 2010, 05:39 PM   #546
udailey is offline udailey  United States
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If he doesnt have GND then why should he be affixing one of the live wires to his chassis?
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Old 16th August 2010, 06:31 PM   #547
troystg is offline troystg  United States
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Quote:
Originally Posted by udailey View Post
If he doesnt have GND then why should he be affixing one of the live wires to his chassis?
Uriah- May I ask you to expand on your question? I am under the impression that you have my responses with Vladamir, concerning power cord connection and entry into a chassis, crossed with his noise / pop issue which is separate.
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Old 16th August 2010, 06:46 PM   #548
udailey is offline udailey  United States
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He has no earth ground. Two wires from the wall, not three. Are you saying he should tie one of these to ground if he does not use your Neutrik solution?
This is where I got confused if I am confused about what you were saying
"At the very least a mains rated power cord hard fixed to the chassis with a gromet / fastener system."
Where is this cord supposed to come from? A live wire to the chassis? Thats what it looks like to me. I didnt see anything in the posts over last few pages to make me think otherwise. If thats not what you meant could you clarify for us, or for me if no one else is confused?
Uriah
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Old 16th August 2010, 06:57 PM   #549
AndrewT is offline AndrewT  Scotland
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I too am lost.
I would like to offer Safety advice, but I have no experience trying to build mains powered equipment that needs a Safety Earth to blow the fuse when there is no Protective Earth wire to the wall socket.
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Old 16th August 2010, 07:07 PM   #550
troystg is offline troystg  United States
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My comment was he should NOT being using speaker cord for mains power. See the speaker wire exiting the rear panel at the lower, center spot...

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I suggested a "standard" power entry connector such as the Neutrik power-con or the common IEC socket.

If he chooses not to use a chassis connector for power then he can use the "old standard" of captured cord where a "fixed" power cord (cord meaning multiply conductor not single wire) is permanently attached to the chassis with a grommet / fastener.

Similar to this type:
untitled
ApexJr Subwoofer Amps

At no point did I ever comment on the ground or noise issue. I only addressed the speaker cable as mains cord safety issue. And I am really hoping he has at least a mains fuse in the chassis.


EDIT: Dude it was REALLY painful trying to find a picture of the "old style" fixed power cord entry.. I think everything has moved to detachable power cords.. Even TV's and cheap DVD players....
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Last edited by troystg; 16th August 2010 at 07:32 PM.
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