LM3886 PCB -New DIyer

[yatgai]

Hallow All

I am new DIYer and learned much from this forum. I am interested in making one LM3886 based chipamp to drive 8Ohm 3 way speakers they have own passive XO built in. My listening preference is Indian classical instrumentals at moderate volumes. For this purpose I feel 50 watt/ channel will be sufficient enough.

Set up in mind is
1. dual mono chip amps ( Non Inverted )
2. no preamp
3. 22k Ohm stereo pot at input
4. Audio source will be CD/VCD player

Amp Specifications are
1. transformer 24-0-24 Centre tapped, 300VA
2. 22k ohm linear pot at input
3. 1uF input capacitor
4. gain of 23 (1+R5/R3)
5. 2200uF capacitor (will they be too big?)

I have designed attached mono PCB in Eagle. Is this workable? Any suggestions / comments to improve ?

PS: I am not an engineer by training so many of the jargon is not understood

Thanks

 

[Dxvideo]

It will work of course!
But;
You may want to use more thicker traces for V+, V- and speaker outputs, if you consider; the main current flow will trace on this ways.
22uF is not enough for feedback line, use 47u or higher to hear deep basses..
1uF is also not enough for input, I would use 4.7u for this position.
You can use 20K instead of 22K for all positions. Since you will use a CD player then you will have 2v RMS input level which is more than ebough for that gain.
And use curved corners for all the traces, electrons don't like cornered wires...
This may help you to make it better;

 

[yatgai]

value of C1 capacitor

thanks dxvideo

i will impliment the changes as suggested.

one question though, changing the value of C1 capacitor from 1uF to 4.7uF will this kill the bass on the output ?

Thanks again

 

[Rembrant]

Dxvideo is right about the corners but not why. I suspect there is a translation problem and he means that 45 degree angles are industry standard. Electrons don't give a damn about having to go 90 degrees. Stick with 90's and 45's nothing in between.

Example of my horrible first try.

 

[lovejenete]

It would work, the only thing is the
capacitor may stop working if the
current flow get deviated by any
means. Else everything is correct.

I must say not being an engineer you
did a wonderful job, No one can be
able to do this in such a perfect manner
without any technical support.

 

[yatgai]

Current Diversion

Thanks lovejenete

"It would work, the only thing is the
capacitor may stop working if the
current flow get deviated by any
means"

> why would this happen, any precautions to be taken ? are the power traces too close? there is at least gap of 2mm between two traces.

"No one can be
able to do this in such a perfect manner
without any technical support."

> thanks for encouragement, yes in the begining I was helped by my engineer colleague, however soon later he changed the job, I suspect my pestering would have been one of the reasons.

Thanks again for your help

 

[TheSeekerr]

Electrons don't give a damn about having to go 90 degrees. Stick with 90's and 45's nothing in between.

True at audio frequencies. Not true universally.

Also, I don't recall LM3886 being available in DIP-8

(Edit: Now that I've posted, it occurs to me that you probably mean your first try at PCB artwork generally)

 

[Francec]

Dxvideo is right about the corners but not why. I suspect there is a translation problem and he means that 45 degree angles are industry standard. Electrons don't give a damn about having to go 90 degrees. Stick with 90's and 45's nothing in between.

Electrons don't care about corners but etchant can become trapped under the etching mask and etch the inside corners of the traces.
Use 45 degrees wherever possible and round other corners if you can.
Frank

 

[Dxvideo]

Ok in fact I did not mean that exactly. But youre right, may be electrons dont care about the wires angle, however if you keep the traces 90° then electrons go more way compared to 45° traces. So that makes difference for electrons and for a final word, ELECTRONS DO CARE about the traces corners angles and dont like 90° corners.
Am I right?

 

[transphere]

As far from what I can remember from my EE EMC classes, electrons do care about corners up to some extent. It's not the longer trajectory, but at really high frequencies, sharp corners will cause more interference problems on your pcb. For audio frequencies this is not the case, but when you're doing stuff in the Mhz region, 45 degree angles are the way to go.

 

[Dxvideo]

Ok this is not the issue of this thread I guess..
Anyway,
Dear Yatgai, the capacitors (1u and 22u) determines your amplifiers low cut frequency. If you keep those values then you will feel some lack of deep basses.
With these resistor values 47u and 4.7u will give you the best bass performance..

 

[yatgai]

Thanks dxvideo

i have made the changes as per your suggestions in the schematic

time to get my hands dirty. hope i donot get dc offset and RF oscillations

i will keep the forum posted on the developments.

Thanks you all for help.