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Chip Amps Amplifiers based on integrated circuits

Bought a XY LM3886 Kit.
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Old 26th March 2012, 06:25 PM   #71
AndrewT is offline AndrewT  Scotland
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Originally Posted by fabricated View Post
Good job on cutting the three ground "straps?" around the bottom side of C4, that is not easily done.
a sharp knife, or craft knife, or scalpel can all be used to cut the bridges. Just take your time and use a magnifier if you need such.
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Old 26th March 2012, 06:45 PM   #72
Aguilabrava is offline Aguilabrava  United States
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AndrewT:

The AC voltage here in USA is 120V. When I measure the actual voltage coming out of the wall outlets, I get a reading of 124.7 volts. I have read that a difference of +/- 10% in mains AC voltage wouldn't make any difference. My 10% would be 11.5 volts since the transformer is rated at 115V AC. Which means that I'm still save at 124.7 volts, since 115 volts plus 11.5 volts is 126.5, and I am at 124.7, correct?.
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Old 26th March 2012, 06:47 PM   #73
Aguilabrava is offline Aguilabrava  United States
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AndrewT:

Did you read post #69 regarding the C4, C5 capacitor values?
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Old 26th March 2012, 06:49 PM   #74
Aguilabrava is offline Aguilabrava  United States
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Originally Posted by AndrewT View Post
a sharp knife, or craft knife, or scalpel can all be used to cut the bridges. Just take your time and use a magnifier if you need such.
I used a Dremel with a 25mm dia. cutting wheel. It was easy, it just took two seconds in each cut, but the cutting wheel is too big, it can be done much better with a smaller diameter cutting wheel, I just didn't have one at the time...
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Old 26th March 2012, 07:11 PM   #75
peranders is offline peranders  Sweden
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Bought a XY LM3886 Kit.
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Originally Posted by lanchile View Post
Before soldering ALWAYS scrape legs of parts until they get shiny and the same goes to boards, that way it will make good joins. Be aware of cold soldering!!!
It's not necessary to scrape the legs. Do you know any pro doing that?
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Old 26th March 2012, 08:26 PM   #76
AndrewT is offline AndrewT  Scotland
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Originally Posted by Aguilabrava View Post
AndrewT:

The AC voltage here in USA is 120V. When I measure the actual voltage coming out of the wall outlets, I get a reading of 124.7 volts. I have read that a difference of +/- 10% in mains AC voltage wouldn't make any difference. My 10% would be 11.5 volts since the transformer is rated at 115V AC. Which means that I'm still save at 124.7 volts, since 115 volts plus 11.5 volts is 126.5, and I am at 124.7, correct?.
a 115:28+28Vac transformer running on 120Vac and then a +6% for maximum supply condition and you will be over the 84Vdc max of the 3886.
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Old 26th March 2012, 08:28 PM   #77
AndrewT is offline AndrewT  Scotland
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Originally Posted by Aguilabrava View Post
AndrewT:

Did you read post #69 regarding the C4, C5 capacitor values?
post54 explains.

What part needs further explanation?
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Old 26th March 2012, 08:33 PM   #78
AndrewT is offline AndrewT  Scotland
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The only time I scrape lead legs for soldering is when I can see an insulating film over the solderable end.

That insulating film could be the enamel of wire or it could be one of the copper oxides.

If the lead legs are tinned or tin plated or silver plated then as soon as the hot solder and the hot flux flows over the wire end the flux boils off any of that soft corrosion. That's why they sell us pre-coated ends on the leads.

BTW,
I do not have a solder pot, nor a way of ensuring the pot temperature suits the next soldering job. For these reasons I do not trust the claim of self soldering insulations on some enameled wires.
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Last edited by AndrewT; 26th March 2012 at 08:35 PM.
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Old 26th March 2012, 10:27 PM   #79
Aguilabrava is offline Aguilabrava  United States
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AndrewT:

Using the second equation in post #54, using C5 as 4.7uF, I have a result of 48.86, which would indicate to use the 47uF 50V capacitor in C4 instead of the 22uF 50V recommended in the kit, is this correct?.

I couldn't really determine the value of C5 using the previous equation you posted in post #53, I don't even know what "Low Frequency Response" to choose for the amplifier, this is way beyond my level of knowledge, that's why I included all the info I could, even the speakers I will be using to play music with this amplifier.

Again, I used all the values recommended (22K Ohm, 1K Ohm and 10 Ohm for Zobel)) in the resistors, I just upgraded them to 1/2 watt.

Now, back to the dilemma, is it OK then to use a 47uF 50V cap in C4 location and the 4.7uF MKP in C5, or should I use the 22uF in C4?.
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Old 27th March 2012, 04:21 AM   #80
lanchile is offline lanchile  United States
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Quote:
Originally Posted by peranders View Post
It's not necessary to scrape the legs. Do you know any pro doing that?
working with a technician who has been in this business for more than 30 years I learned that scraping legs ( caps, resistors, diodes, transistors etc) will ensure you will have a better join. it is like a plummer when they solder those copper pipes and they ALWAYS scrape with sandpaper making sure is shiny to make better contact and then they solder. beside it will not take too much time. He used to test and measured parts before and after soldering parts . I also learned how to solder STK's and IC's.(many legs) He said for example, if a chip has 12 legs, I should solder leg 1 then leg 12...2 then 11...3 then 10....etc and always not rushing the job. That way you do not "concentrate" all the heat on one side (unless you want to wait a little bit from soldering). I know many will jump here saying that is BS, But to me I find it smart!. You solder your way and I solder my way right?. I learned a lot from him, and staff that you do not learn in a electronic school. I guess you learn by experience and mistakes. I read Bryston technicians Do test the parts before and after they solder them, so I guess my friend was not so wrong after all.
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