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Old 22nd September 2012, 08:11 AM   #61
AndrewT is offline AndrewT  Scotland
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is post60 relating to post59?
or something else?
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Old 22nd September 2012, 06:11 PM   #62
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yyes, sry my english its not good enougth, o i mean what i do whit the ground of the entry, how i connect it to the ground of the circuit? whit a capacitor o just in 1 point?
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Old 22nd September 2012, 10:32 PM   #63
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Some update, what do u think now guys?

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Old 23rd September 2012, 02:29 AM   #64
gootee is offline gootee  United States
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necrofago,

Not too bad.

One probably-significant improvement would be to put the output and Zobel-network ground between the two large electrolytics, because the decoupling caps should usually connect between power pins and load ground.

It should be easy to move C7 toward the left and then turn R7 by 180 degrees, etc. That will also help to make the positive and negative rails closer to the same length, after the large decoupling caps, giving a more-symmetric transient response.

Then you could also make all of the ground plane on the right-most 1/3rd of the board be signal ground.

Regards,

Tom
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Old 23rd September 2012, 06:45 PM   #65
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Thanks gootee, i migth something like this? or GND Ouput also between C7 and C8?

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Old 23rd September 2012, 07:56 PM   #66
gootee is offline gootee  United States
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Quote:
Originally Posted by necrofago View Post
Thanks gootee, i migth something like this? or GND Ouput also between C7 and C8?
necrofago,

Yes, output ground also between C7 and C8 (or close, and equal distance from both). Sorry, I know that will take a little bit more work. But that's where it should be. (Actually, you will have a lot more layout freedom, with that change.)

I would try to get the Vrail connections for all four of the decoupling caps as close to the chip's Vrail pins as possible, too, and symmetrically distant from them if possible.

But it would be much better to use more than one smaller cap, in parallel, instead of one big one, for each rail. That would make the layout easier, too.

If at all possible, I would use a two-sided PCB, with the top layer as all ground. The connections for the 0.1 uF caps need to be right AT the chip's power pins. And the planar ground would give the lowest inductance and resistance.

The accuracy of the system's transient response (any fast-changing signal currents) will depend on having low-inductance (and low-resistance) decoupling, i.e. very short connection lengths and/or large-size connections to those capacitors, which need to connect between the chip's power pins and the load and power ground.

Big power and ground planes are best, for that. Also, using multiple parallel smaller caps instead of one big one is best for that, with or without planes. (Multiple parallel caps could also make the connection lengths somewhat less critical.)

-----------------------------

See how the music signal IS the capacitor currents:

http://www.diyaudio.com/forums/solid...ml#post3117390

That was showing PSU reservoir caps but the fast transient changes must come from the decoupling caps, near the load, exactly the same way.

The best way to do it would probably be to use a big bank of parallel caps for each rail, like Terry Given suggests, starting at post 1009, here:

Power Supply Resevoir Size

Also read more, such as posts 1010, 1016, 1019, 1022, and then also post 1207 (with an example PCB layout) at

Power Supply Resevoir Size

and then the second half of post 1214 and all of post 1215, and maybe some others if you still have questions.

Edit: You could put the arrays of decoupling caps on the PCB you are working on in this thread, if you simply used a 2-sided PCB. And that would also enable you to improve a few other minor things in the layout.

Cheers,

Tom

Last edited by gootee; 23rd September 2012 at 08:05 PM.
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Old 23rd September 2012, 08:45 PM   #67
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Tom, the power supply for this amp got 10x 1000uf and some ceramic per rail, i think its good enougth.

Ilt ry to move the GND ouput between the caps, but adding more caps in this pcb will be hard cuz the space.
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Old 23rd September 2012, 10:07 PM   #68
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Ok, i put 4 more caps, 2 of 1000uf total, and 2 0.1uf smd each, and some rework on layout.

What do u think?

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Old 23rd September 2012, 11:37 PM   #69
gootee is offline gootee  United States
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It's better. And it's OK.

But if you are feeling motivated, then check the diameter and lead-spacing of 220uF and 330uF and 470 uF caps in that voltage range. If you could replace each (or just one) 1000uF with 2x 470uF, or 3x 330uF, or 5x 220uF, it would be that much better.

You might want to try to pull Cmute in a little. If it's against (or too near) the heatsink, it might age too quickly.

Last edited by gootee; 23rd September 2012 at 11:41 PM.
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Old 24th September 2012, 08:47 AM   #70
AndrewT is offline AndrewT  Scotland
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Consider multiple PIN Pitch options for all capacitors.
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