Dual3886

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Readme.txt

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Joined 2003
Long time reader, first time topicwriter!

This summer I have desided to do something about my spare lm3886.

objectivs
- two lm3886/board
- versatile module that can be configured in stereo, bridge and parallel mode
- on board power supply - just add transformer
- diy etched pcb

I use Eagle light which means that I'm limited to a board size of 100*80mm. Since I'm planning to etch my own pcb I want to make a single sided one. This makes it a little bit cramped on the pcb!

I would very much like you to take a look at my board before I start to etch and buy components.
Should I give it a try? Is there any obvious errors? The "groundplane" seems a bit anorectic to me...

Schematic
Board

/Per
 
R

Readme.txt

Member
Joined 2003
One quick glance..the servo IC o/p should be fed to inv i/p of 3886 ? right ? or interchange the servo ic i/p pins either way same result...
Click to expand...

That's true! I knew it was a good idea letting someone else check my work. Thanks a lot!

Why don't you try using inverting amps for both stages?

That may eliminate your DC servo and some other parts too. Things will be less cramped too.
Click to expand...

Let's see if I understand you.
If I decide to keep the dc-servos, I belive the number of components is almost the same in inverting and non-inverting mode. To eliminate components I have to get rid of the dc-servos, right? Is an inverting lm3886 a better choice without dc-servos?
 
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carlmart

Member
Joined 2001
preciseaudio.com

Let's see if I understand you.
If I decide to keep the dc-servos, I believe the number of components is almost the same in inverting and non-inverting mode. To eliminate components I have to get rid of the dc-servos, right? Is an inverting lm3886 a better choice without dc-servos? [/B]
Click to expand...


To start with I think servos have to be different for nulling DC in inverting amps.

But that is not my point. The main purpose of DC servos is to cut DC offset. On non-inverting amps you use a large capacitor on the feedback. On inverting amps you can get away with smaller cap, usually series 4.7uF or less, that can be a film type.

Parts count is also less, but not that much really, perhaps one resistor and one capacitor less. It is if you don't add the servo.

IMHO a well implemented inverting gainclone will sound a bit better than a non-inverting one, but that may not be as important if you use things like good de-coupling and short pcb paths. Using less parts may make such paths really short.

That's all I intended to say.
 
R

Readme.txt

Member
Joined 2003
Where'd you get those inductors? 0.7µH, right?
Click to expand...

I just wired the inductors myself. 13 turns of 1.3mm enamel insulation copper wire around a 10mm metal drill. That's how the Elektor magazine did it in one LM3886 article back in 1998 I belive.

And the sound. I have only tested it with a pair of crappy speakers and input from my integrated computer soundcard to make sure it worked properly. There was no problem but I can't say if it sound good or not.
 
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