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Old 14th March 2014, 09:08 AM   #1
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Default Is this layout OK? Advice please :)

Hi all,

I have done a quick PCB design for my active crossover circuit, and Id like to get some opinions on it, if possible.

Its a single side board, with top board links in red.

At the moment its a single mono channel, but I am thinking of duplicating the design for a stereo version.

Is there any particular advanatage to doing this? Its likely Id have to rearrange the incoming supply Caps and redraw the rails I reckon.

Click the image to open in full size.

So there it is ^^^^ Opinions and constructive criticism welcome, and in fact I invite it

Thanks for your time.

I have just noticed that i seem to have the IC decoupling cap polarity reversed.....
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Old 14th March 2014, 05:32 PM   #2
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It would be good to add the current schematic to this thread.
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Old 14th March 2014, 07:10 PM   #3
AndrewT is offline AndrewT  Scotland
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The feeds in & out of the big capacitors share a length of trace.
Don't do it that way.

Bring the IN trace up to the cap terminal. Take the OUT trace away on the other side.

This way the ONLY part of the in out route that is shared is the terminal pin.
So keep that short, as short as the PCB mounting will allow.
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Old 14th March 2014, 07:12 PM   #4
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Could you highlight the Signal Return trace/s along with their Signal Flow routes.
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Old 14th March 2014, 09:26 PM   #5
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Default ah yes...the sch.

Sure ill add the schematic.

Ill also edit the diagram to show details, since i don't quite follow you Andrew.

though this is likely because I haven't provided a lot of info

Give me a couple of days and ill update.

Again, thanks for the interest.
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Old 15th March 2014, 10:21 AM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by mondogenerator View Post
............... i don't quite follow you Andrew.
.............
Which part, or parts, do you not understand?
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Old 15th March 2014, 11:27 AM   #7
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I'm no expert on PCB layouts so take this with a large grain of salt, but I would question the placement of the small decoupling caps. Everything I have read with respect to layouts for opamps is that the decoupling caps should be as close to the opamp pins as possible. I've just ordered some 100nF NPO ceramic SMD caps in 1206 size. The idea is to have a ground plane on the upper side of the pcb and put the caps from power pins to the ground plane. Alternatively it would be easy to mount the caps on the track side of the pcb right up to the power pins, if you had a ground trace coming close to the power pin (which you should be able to do with the way you are routing the power at the moment.

Perhaps it doesn't matter for the IC's you are planning on using, but it doesn't hurt to have the facility available in case you find they do need better decoupling.

Tony.
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Old 17th March 2014, 05:34 AM   #8
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Andrew: after reading again i think i understand. The Y - shaped in/out trace should be straight and shorter traces?

Wintermute: grounding is a difficult one. I did consider routing the ground with the supply traces but felt i would either be left with too small a gauge traces, or simply that id be pushing it to fit three traces thru the IC.

The decoupling caps aren't ideal, i was hoping they'd be close enough. The prototype had them soldered on the backside of the board, and i may have to do that again.

Also, whilst I'm also a novice, i prefer a star ground, and a double sided board is difficult with the setup in using for the lithography development. I.e. Homebrew UV box.
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Old 17th March 2014, 12:03 PM   #9
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Default AndrewT: More like this?

Heres a slightly revised supply cap arrangement:

Click the image to open in full size.

Also I found a few mistakes....I may be a while longer fixing my errors.
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Old 17th March 2014, 12:11 PM   #10
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Yes, the IN and the OUT routes are separate traces.

On the IN side the Flow and Return to both capacitors are close coupled. This is some room to move them even closer.

On the OUT side, they are far from close coupled.

If the OUT currents vary (i.e. not - constant DC) then the loop areas times the variation magnitude gives interference on all receiving circuits.
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