Car audio LM3886 + SMPS on single sided board - Page 3 - diyAudio
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Old 13th November 2008, 06:25 PM   #21
ide2003 is offline ide2003  Indonesia
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hi all, thanks for the update rwaudio, checked the link..well how can I missed that one?..I'm a regular visitor of ESP..not an EE though-have major difficulties understanding things , but really loves DIY & audio. I'll try to have 4x50w LM3886-car for a start..wish me luck
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Old 14th November 2008, 02:38 PM   #22
rwaudio is offline rwaudio  Canada
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AndrewT or anyone who's implimented a differential input could you give me a little help with my differential input? Basically I only get good operation when I connect the rca shield directly to signal ground. Using a cap/resistor (tried many values of each) gave increased noise, though slightly better than nothing connected.

As you can tell I'm new to using a differential input, attached is a simple version of what I have on the breadboard right now. Power supply is taken from the output of the amps smps and regulated to +/- 15v.

It's pretty good at rejecting noise from a very crappy bench power supply (completely unusable using normal input buffer, and very listenable with slight noise using the differential input) and it's pretty much silent using my regulated bench supply, however I'm assuming that some cars "could" be more like the noisy bench supply.

I'm also not sure how to impliment a dc blocking cap on the input, if it's as simple as putting a large enough film cap on the signal line before the 22k resistor.
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Old 14th November 2008, 02:58 PM   #23
AndrewT is offline AndrewT  Scotland
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that's not a differential input.
That is an unbalanced input.
Is your source expecting to see a balanced input?
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Old 14th November 2008, 03:16 PM   #24
rwaudio is offline rwaudio  Canada
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Is it not a differential input if the rca shield to ground connection is removed? That's where I need help since that schematic is the only way I could get silent operation using a noisy supply.

The source at the moment is a typical car cd player (alpine cda-9813) so it's expecting a "normal" input.
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Old 14th November 2008, 03:22 PM   #25
AndrewT is offline AndrewT  Scotland
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if the CD player is expecting a normal input then I think Alpine mean an unbalanced input.
Forget differential.
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Old 14th November 2008, 03:24 PM   #26
rwaudio is offline rwaudio  Canada
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Thanks AndrewT, is there a good fairly noise free topology to use for amplifier input? I'll probably be making a few of these for friends etc, and most of them don't have the best quality stereo's. I'd like these to work well and engine noise free, atleast the best I can create.
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Old 16th November 2008, 11:57 AM   #27
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hi everybody !

i'm intersted in this project too and waiting for the schematic and layout.

it must be powerfull and cute amp !

best regards

amir
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Old 17th November 2008, 02:35 PM   #28
rwaudio is offline rwaudio  Canada
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Hello everyone, I haven't cleaned up the schematic yet so I can't post that. But I do have a 99% complete BOM (this does NOT include parts for the preamp board, this is amp/power supply only) The idea of having the preamp board seperate from the main board is for almost unlimited configurability. If you want crossovers, or balanced input or whatever you can imagine, it can be added to the amp. I will be designing a couple versions, simple input, and probably highpass or lowpass crossovers.

Please note, that this version is intended for a subwoofer amplication, as many people have found the large rail capacitors I chose may not provide the best possible sound quality in a mid/hi freqency application, some trial and error may be required.
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Old 17th November 2008, 02:51 PM   #29
troystg is offline troystg  United States
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Old 17th November 2008, 03:56 PM   #30
ide2003 is offline ide2003  Indonesia
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exciting..exciting..now I can start collecting parts, have contacted friend who have large ferrite toroids and an oscilloscope..thanks rwadio..btw, are you using the SG3525? didn't saw it at a glance in your prelim. BOM

TPS
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