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Old 31st July 2001, 02:05 PM   #1
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http://www.national.com/appinfo/audi...ation_Note.pdf

have anyone tryed this applications.
If so is there a circuit layout ?
Im very much interested in making one amp using this idear
for making powered monitors for my band.

jc.
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Old 1st August 2001, 05:13 AM   #2
paulb is offline paulb  Canada
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Smile ESP again

partyjups,

Interesting app note, thanks for posting it. If I ever build an LM3886 amp, I may use this to spread the dissipation across several chips - one of the problems with IC amps is trying to pull enough heat out of them.

If you are thinking of building the Fig. 7 circuit, 2 of the ESP Project 19 (www.sound.au.com) boards could be used; you would have to add the buffer op amp separately and build the boards slightly differently than intended (thus voiding your warranty . Note the buffer op amp must run from lower voltages than the power amp chips; you'd have to add regulators of some kind.

If whatever you're driving with can stand a 250-ohm load, you probably don't need the buffer.

If you want to build the Fig. 11 circuit with the servos, you'd have to add a separate board with the servo op amps and wire it into the key points of the ESP boards.
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Old 1st August 2001, 09:37 AM   #3
djk is offline djk
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Why screw around with those things? A single pair of Semelab BUZ900D/905D will give you 200W. Use a $6 Pass A40 pcb to drive them. Check out this page
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Old 1st August 2001, 12:57 PM   #4
paulb is offline paulb  Canada
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Better protection, for one thing. The ICs have built-in SOA. Nothing like taking out a set of speakers too when your amp goes.
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Old 2nd August 2001, 07:10 AM   #5
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"paulb Better protection, for one thing. The ICs have built-in SOA. Nothing like taking out a set of speakers too when your amp goes. " I will repeat.Those things are pathetic. The BUZ900D/905D don't need SOA protection because of their design.And none of the protection in the LM3886 will protect the speaker if the amp blows.
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Old 2nd August 2001, 01:45 PM   #6
paulb is offline paulb  Canada
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djk, I'm not putting down your idea with the big FETs. I think it's fascinating, and I intend to have a closer look. But partyjups asked about the 3886 design. I personally think that power amp ICs are a good way for someone to get started building amps because they're simple to use, especially if you can buy a PCB. The built-in protection helps keep obvious blunders from going up in smoke.

I'm not sure why you think they're "pathetic"(there's a lot of unsubstantiated opinion thrown around these forums). I have a PCB for a 3886 amp, and I intend to try it someday. If it sounds terrible, I won't take it any further than that. I think partyjups was intending to use this on stage; surely the fidelity requirements for him are not so stringent.
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Old 2nd August 2001, 09:48 PM   #7
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LM3886 don't smoke, it explodes, really!

I have one LM1876 (same family and same SPiKe protection) with a small crater in its body... If I can remeber it was a short on one pin.
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Old 3rd August 2001, 01:31 PM   #8
paulb is offline paulb  Canada
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Yes, the pins are too close together. I had thought of trying a handwired board but gave it up quickly when I saw the part.
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Old 5th August 2001, 11:16 AM   #9
djk is offline djk
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"I'm not sure why you think they're "pathetic"(there's a lot of unsubstantiated opinion thrown around these forums). " The 3886 has foldback current limiting.If you read the spec sheet it says the power rating is for an INFINITE heat sink.Since the limiting is also temperature sensitive any real heatsink will cause the protection to activate unless you run the thing at about half power.Foldback current limiting driving an inductive load makes "farting" and "popping" sounds that are hell on your tweeters as well as sounding bad."Pathetic" may not be a strong enough term to describe this part.If you want to buy four of these fine quality parts and parallel and bridge them with current balancing resistors and DC servos for each module go right ahead.In my mind it is both a waste of time and money.
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Old 7th August 2001, 03:46 AM   #10
paulb is offline paulb  Canada
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djk,
Thank you. I see far too much scorn thrown around here with nothing to back it up.
Rod Elliott also notes that you shouldn't drive these puppies anywhere near where the protection kicks in. Caveat emptor.
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