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Chip Amps Amplifiers based on integrated circuits

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Old 5th February 2009, 04:08 PM   #161
AndrewT is offline AndrewT  Scotland
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I would do the opposite.
Increase the current through both 140s & 139s to ~12mA.
They run at almost constant current because Vbe of the next transistor hardly changes for big changes in output current.
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Old 8th February 2009, 11:56 PM   #162
keaster is offline keaster  Canada
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Hey everyone, i'm new to the forum and came across this project a couple of weeks ago and now i'm hooked and want to build a 2 ch stereo amp.
The thing that i'm still confused about is the transformer, it seem like there is a lot of options I usually buy from digikey.com and when looking through there site it asks for Parallel Output Voltage @ Current and Maximum Power now I know for 2 amps, I need a dual secondary so if anyone can point me to the right one to buy from there because this seem to be the most expensive part of the whole project prices ranging from 60 to 120.

Or if there is a better place to get them from in Canada that would be great too!

Thanks
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Old 9th February 2009, 01:21 AM   #163
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Plitron in Toronto is one of the better toroid manufacturers.
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Old 9th February 2009, 09:02 AM   #164
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by keaster
i'm new to the forum and came across this project a couple of weeks ago and now i'm hooked and want to build a 2 ch stereo amp.
download the datasheet and any other information the manufacturer publishes for your potential chip.
Decide what speaker impedance you want to use, now and in the future.
Consult the datasheet and find the maximum DC voltage the chip can accept for your chosen worst case speaker impedance.
Now select a transformer AC voltage to give that maximum DC supply.

If you use a 3886, then for 4ohm speakers you can use 15Vac or 16Vac or 18Vac and if you're careful to keep the chips cool you can get away with 20Vac.

Select a centre tapped or dual secondary for a monoblock amplifier and use a single rectifier arrangement.

For a stereo amplifier, select a dual secondary transformer and use a dual rectifier arrangement.
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Old 9th February 2009, 02:10 PM   #165
keaster is offline keaster  Canada
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Thanks for the quick reply, Is there one that you would recommend?

This is what I found any thoughts?
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Old 9th February 2009, 02:10 PM   #166
keaster is offline keaster  Canada
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Sorry forgot the link
http://www.plitron.com/shopping/shopexd.asp?id=171
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Old 9th February 2009, 02:36 PM   #167
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That link is a 38Vac which is way to high.
This is the 20Vac version..

http://www.plitron.com/shopping/shopexd.asp?id=163
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Old 9th February 2009, 03:59 PM   #168
AndrewT is offline AndrewT  Scotland
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Keaster,
have you even read the datasheet or application note for the chipamp?
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Old 13th February 2009, 02:05 AM   #169
keaster is offline keaster  Canada
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Sorry if I sound dumb, but im very new to this and its something that I want to try building and dont want to get it wrong ive read the data sheet.

Im just trying to find the best place in Canada to get the transformer from
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Old 13th February 2009, 07:41 AM   #170
AndrewT is offline AndrewT  Scotland
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read the datasheet again.
What speaker impedance have you decided to design for?
Find the sections that deal with supply voltage and speaker or load impedance. Follow the manufacturer's advice. If there is a part you don't understand ask a specific question. We're here to help.

Find the sections that deal with heatsinks and power dissipation.
Here, I suggest you at least double the dissipation capability that National recommends as a minimum.
Again come back with any or all questions.
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