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Old 2nd September 2008, 06:29 PM   #1
kanifee is offline kanifee  United Kingdom
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Default Bridged LM3886 psu.

I have 4 LM3886 ic's sitting doing nothing and really want an amp with a bit more weight behind it than my single chipped lm3886 has. Ive been looking into bridged and parallel setups and have come to the conclusion that (maybe incorrectly) bridged is better as long as you take into account the extra heat etc.

Im going to use matrix board and semi's referance for the bridged circuit but what id like is to A, know what sort of freedom i have to experiment with caps in the audio circuit. And B if any one has a schimatic for a power supply i can use with this with a 25-0-25 trafo?
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Old 2nd September 2008, 07:06 PM   #2
zei is offline zei  Sweden
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Kanifee my friend.

Search for TwistedX by Russ White on this forum

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Old 2nd September 2008, 07:30 PM   #3
kanifee is offline kanifee  United Kingdom
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Sweet, BTW you have mail
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Old 2nd September 2008, 11:13 PM   #4
kanifee is offline kanifee  United Kingdom
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http://www.diyaudio.com/forums/attac...amp=1098741354

Any good for what i need?
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Old 3rd September 2008, 05:14 AM   #5
sangram is offline sangram  India
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A 25-0-25 trafo will give you roughly 35V rails, quite a bit higher than is really required for bridge configuration. Unless you have 16 ohm speakers, that is. If not, expect SPiKE to kick in very, very frequently at high levels.

I built a parallel amp myself, and couldn't be happier. Using good quality resistors instead of generic (only in the feedback position though) really helps illuminate differences between rigs, sources and recordings. And having about 20 amps of current on tap helps drive some inefficient loads, and also gives the chipamp a lot more grunt.

That PSU will work, but with the caveat of a high rail voltage. Ideally 20V transformers should be used for 28V rails, for a bridge setup driving 8 ohm speakers. And you do need to take care of the heat.
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Old 3rd September 2008, 07:07 AM   #6
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Default Re: Bridged LM3886 psu.

Quote:
Originally posted by kanifee
Im going to use matrix board and semi's referance for the bridged circuit but what id like is to A, know what sort of freedom i have to experiment with caps in the audio circuit. And B if any one has a schimatic for a power supply i can use with this with a 25-0-25 trafo?
What's wrong with semi's reference PSUs in AN-1192 or AN-1849? The latter uses 2x24V, which is similar enough to your 25-0-25 idea.
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Old 3rd September 2008, 07:47 AM   #7
kanifee is offline kanifee  United Kingdom
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Default Re: Re: Bridged LM3886 psu.

Quote:
Originally posted by pacificblue


What's wrong with semi's reference PSUs in AN-1192 or AN-1849? The latter uses 2x24V, which is similar enough to your 25-0-25 idea.

I had a look at semis referance PSU and to be hounest i suppose i dont really understand it (im still learning especially were schimatics are concerned.
Click the image to open in full size.
The only part i really understand is the two on the left and im unsure how these work together, any one care to elaborate the schimatic?
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Old 3rd September 2008, 11:18 AM   #8
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This could help you to get a grip on power supplies.

After that you look at the Bill of Materials in AN-1192 and compare the designators with the schematic you posted. Things will hopefully become clearer then.

By the way, the upper two parts of that schematic are for the power amplifier, which is the interesting part for you. The lower three parts are for the op amps that are used as DC servos in the BPA-200, so probably not so important for you to start with.
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Old 3rd September 2008, 12:24 PM   #9
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Also, check out this spreadsheet to get an idea on power output, heat levels, etc. For bridged, put half the impedance of your speakers in the impedance field.

http://www.national.com/appinfo/audi...gn_Guide15.xls
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Old 3rd September 2008, 12:32 PM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
bridged gives double the power into double the load impedance.

If you use +-35Vdc for your supply rails then each 3886 chipamp can give about 60W into 8r0.

When you bridge two 3886 chipamps off +-35Vdc supplies you should get 120W into 16r0, if the Power Supply is correctly sized to allow 120W at your chosen bandwidth.
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