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Old 15th January 2009, 06:31 PM   #11
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If you go for an unregulated supply with 4 Ohm speakers, use a 2 x 18 V transformer. You can use up to 2 x 22 V, but then you need an enormous heatsink and should take the unisolated package.

A regulated supply adds complexity and expense. For a first time project you should avoid that.

Adjustable voltage? There is an upper limit you can use. Setting the voltage below that means reducing the amplifier's dynamic headroom and increasing the heat dissipation across the regulators.
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Old 15th January 2009, 06:55 PM   #12
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Default Re: Chip Amp General Question

Quote:
Originally posted by bluetech
If I take a Chip Amp (LM4780 for example) and connect it as per data sheet, is it gonna be ok?
Yes.

This is exactly the right approach. You may pick up some finer points from people here who have experience of the chip, but as a general rule for ANY unfamiliar component this is the way to start.

What else ya gonna do?

w
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Old 15th January 2009, 08:09 PM   #13
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just a clarification, I am talking about PS output, not transformer output

I agree reg. psu may be more complex than unreg. but I still think it's a doddle on a perf board

the advantage is that you can change the voltage according to taste

I found optimum sonic performance at +/-28VDC but that is my taste!
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Old 15th January 2009, 08:24 PM   #14
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Default LM3886

I'm with everyone else- its easier to use two LM3886 than a single LM4780 cause of those many tiny pins on the 4780. I've made both; and did a LM3886 on perfboard- no PCB required, but you have to angle those pins in there.

Do not use the single rail schematic on the data sheet, use the split supply and you will be fine. There are lot of schematics out there- I've got a few on my web site (link in my signature line).
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Old 15th January 2009, 08:41 PM   #15
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Default Re: LM3886

Quote:
Originally posted by lgreen

Do not use the single rail schematic on the data sheet,
Hi,
Have you tried it? I have and it's pretty good, especially for lower power use.
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Old 15th January 2009, 11:03 PM   #16
lgreen is offline lgreen  United States
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Default Re: Re: LM3886

Quote:
Originally posted by MJL21193


Hi,
Have you tried it? I have and it's pretty good, especially for lower power use.

No I have not, but its more complication for the first-timer. I was against it due to difficulity not sound quality-- though my guess using pure speculation is that the dual rail would sound better--- you've got me there though as I have never tried it.

Edit- I love that album on your avatar! Moving pics is awesome too.
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Old 16th January 2009, 08:34 PM   #17
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Hello everyone and thank you for your comments.

Igreen,
I saw in your schematic that you use a 2W resistor only in the output. Is that the only place that needs a high watt component?

What about the caps? what volt rating i should use. I saw in an other schematic was used 40v caps with 35v supply?

I'm thinking of using this power supply. what do you think?

http://sound.westhost.com/project04.htm

Nice project by the way.

Thank you
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Old 16th January 2009, 10:19 PM   #18
lgreen is offline lgreen  United States
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That power supply is great and can be used without any problems. May want to consider a "snubber" power supply (R and C across the + and - of your power supply to remove harsh high frequencies), search here for "snubber" or "snubberized" as posted by CarlosFM.

Yes, the 2W resistor is part of the Zobel network on the output terminal. You do not need any other high power parts, unless-

1. you put in a snubber power supply, the R should be high power.
2. You hook an LED to the power supply, you will need a 1/4 W or higher resistor to limit its current. Do you know how to do this? search here and internet for "LED equation" or "LED calculator"

You don't want to use 40V caps with a 35V supply. If there is a surge in your AC wall voltage the rating will be exceeded, plus good design calls for a wide saftey margin- double the expected voltage is good practice. There are standard voltages for Caps so pick the closest 50V minimum, 63 if you can or preferably 80V to impress the bigshots at this website.
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Old 16th January 2009, 10:38 PM   #19
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Even in the Boucherot cell a 1/4 W resistor should be enough. 2 W at that place would be something for a much bigger amplifier or to cover up a design issue like oscillations or insufficient airflow in the case.

The voltage rating for the caps should always be higher than the voltage they will be used on plus a safety margin of at least 25 %. 40 V capacitors with 35 V rails is already a tight match.

Project04 is a solid standard design except for the earth loop breaker, which a nice-to-have. Consider adding more capacity to the rails, especially with 4 Ohm speakers.
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