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Chip Amps Amplifiers based on integrated circuits

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Old 16th December 2012, 09:53 PM   #1
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Talking building a lm386 bass bost help

Hi DIYAudio community
I want o build the lm386 with bass boost but i am not that knowledgeable about building pcb...
I got a chance to spend a few hrs with eagle software and the attached images are what I did.

Is the RED lines correct. I suspect that they are too close. they are negative traces. one for input(-) and the other for output(-).
if they are incorrect can someone please help me place them correctly.

and btw what exactly does a Bypass cap does in this circuit, if used. I noticed the line is not solid. will it help reduce noise? i know that the basic description is to bypass current but please forgive my ignorance. if it helps what cap value would you recommend.
sorry if I'm asking for too much.

thanks for your help

images are from eagle software
Attached Images
File Type: png lm386bassboostschematics_zps8faa59c6.png (52.8 KB, 131 views)
File Type: png lm386bassboost_zps98c8bc3f.png (108.6 KB, 121 views)
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Old 17th December 2012, 03:20 AM   #2
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U have designed it like an RF circuit. The ground plane is unnecessary. Make the tracks bigger, and the components to be laid closer. Smaller the better. That 10K is a volume control, so find a potentiometer and fix it on the edge physically so that u can fix a knob for controlling the volume.

I don't know what u r going to hear with a 400mW amplifier...Your mobile has a more powerful amp nowadays.

Gajanan Phadte
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Old 17th December 2012, 06:57 AM   #3
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Thanks for the help.
I know its a weak ic but I just want to proof concept with it. If I can make this work then I'll jump into deeper waters. lol

btw how about the grounds from jumpers, line in and line out aren't they too close.

got it revised.
Attached Images
File Type: png lm386bassboostR1_zpse286d55a.png (76.8 KB, 105 views)

Last edited by D Bohique; 17th December 2012 at 06:59 AM. Reason: can't seem to get the pic attached
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Old 17th December 2012, 07:57 AM   #4
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Proximity of tracks does not matter in such simple circuits.

First, there has to be a capacitor of about 100mfd and rated for more than dc supply, across the V+ and ground close to where the power enters the board. The point where ground is connected to this filter capacitor has to be used as star ground point. Your input ground connection has to reach this star without any other branching.

If u r going to etch this pcb yourself, avoid tracks between the IC pins as it is nearly impossible to etch by DIY methods unless u use photograhic method.

The R3 should be a potentiometer.

Gajanan Phadte

Last edited by gmphadte; 17th December 2012 at 07:59 AM. Reason: added content
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Old 17th December 2012, 06:57 PM   #5
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I got it redone. If I understood your instructions well. hopefully this one is ok for etching.

I will be using the laser toner/ ironing the copper clad method I saw on the net.
I know the trimpot is not ideal but when I tried using the regular pot from software it did not wanted to connect to the tracks somehow (I'm a noob I guess).

as you can see although a bit messy. I got C5 at the IN and VS.
from Vs goes to Pos cap and to IC# 6 pin. then NEG from IN and to Neg Vs together. I did the best I could. Had to vias pin 2&4.

thanks for your support
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File Type: png lm386REV2_zpsb8900442.png (102.0 KB, 87 views)
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Old 17th December 2012, 09:53 PM   #6
JMFahey is offline JMFahey  Argentina
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Maybe this one is fine, didn't check all connectivity, but I suggest you use much thicker tracks.
These seem to be 10 or 12 Mil ; for home etching use at least 30 Mil, and in many places you will be able to go to 50 Mil ... and for ground use 100Mil if possible, "thinning" only when absolutely necessary.
Also enlarge IC pads or even better use "IC" pads, the rounded rectangle ones, and make pin 1 a full rectangle.
Or draw a small dot by it, to avoid mounting the IC the wrong way, by mistake.
As an example, here's the PCB of my 12V 60W MosFet amplifier, used in battery powered Guitar/Bass/PA combos:
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File Type: gif MOSPWR2.gif (22.9 KB, 78 views)
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Old 18th December 2012, 01:08 AM   #7
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I have 40mil set on the Net classes width box. same value over design rules "sizes". but the tracks do looks kind of skinny.
does that means the pcb looks good to etched?
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Old 18th December 2012, 01:44 AM   #8
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ok got it. I found out how to fix it. every thing was upped to 40 mil.
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Old 18th December 2012, 06:01 AM   #9
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You produced a short between pins 5 and 6.

Check if the trimmer is mounted in a way that clockwise turning increases the volume. Are you sure you want to need a screwdriver each time you adjust the volume? And you want to scratch C1 with the screwdriver every time?

You should use the correct values. You need F not mF for the capacitors. The smaller values are nF instead of 0.0xx F.

Although they may not influence the function, looks are also important. Try to align components where possible, e.g. C2 and C3 vertically, C1 and C4 horizontally. Space things equally, e.g. make the distance between C1 and C4 the same as between C4 and C2.

First of all however use the correct packages. C1, C3 and C4 will not be electrolytic capacitors. C4 should be a ceramic or film cap, C1 and C3 film caps. They have different shapes and sizes and that will make it easy to improve the layout. Try to move components around until you have the shortest possible paths everywhere.
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Old 18th December 2012, 08:36 AM   #10
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The potentiometer, if u don't know how it looks. The one u have selected is a multiturn preset may be called potentiometer in the software.

Gajanan Phadte
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File Type: jpg potentiometer.JPG (10.6 KB, 65 views)
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