First PCB Layout
« on: April 04, 2018, 04:04:28 PM »
Hey, tying to teach myself eagle. Just simple stuff for extender cards, guitar pedal, etc...

I drew up this little pcb for adding phantom power to a mic pre. The bottom layer is all ground plane.  I did a copper pour on the top but I don't know if that sort of thing is necessary.

If anybody feels like looking it over and giving some feedback it'd be much appreciated.


boji

Re: First PCB Layout
« Reply #1 on: April 06, 2018, 01:07:16 AM »
You making them yourself? If so, perhaps increase the polygon pour isolation a wee bit, just to be safe; the cap pads look awfully close to mask. 

Minor adjustment: Perhaps give PAD2 a bit more room away from the neutrik? 

Re: First PCB Layout
« Reply #2 on: April 25, 2018, 06:38:18 PM »
oh man, never get a notification.

 I redrew it a little bit with better clearances and couple things moved about. I didn't allow for the thickness of the front panel so cut down on some of the area under the xlr.

Quick question: Is there a standard hole to hole measurement for a 1/4 watt resistor?  I see that they are ~6.3mm long.

Thanks,

ruffrecords

Re: First PCB Layout
« Reply #3 on: April 26, 2018, 03:41:11 AM »
The standard through hole quatrer watt resistor footprint is known as RC05.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Harpo

Re: First PCB Layout
« Reply #4 on: April 26, 2018, 06:54:39 AM »
"for a 1/4 watt resistor"
consider to recalculate the rating needed of R1 and R2 by applying ohm's law, just in case a shorted mic cable is connected with phantom power activated, IE  P=U2/R when you fill in 48 for U and 6800 for R ...
A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.  -Douglas Adams

Re: First PCB Layout
« Reply #5 on: April 26, 2018, 02:47:20 PM »
The standard through hole quatrer watt resistor footprint is known as RC05.

Cheers

Ian

Awesome thanks!

"for a 1/4 watt resistor"
consider to recalculate the rating needed of R1 and R2 by applying ohm's law, just in case a shorted mic cable is connected with phantom power activated, IE  P=U2/R when you fill in 48 for U and 6800 for R ...

Well damn...that's a good point--.339 watts.  I will upgrade to 1/2watts to be safe.

I received the rev A1 boards from dirty pcb.com.

I'm getting 48v on the output to the mic pre. I'm not sure why though. Any thoughts?

here's the schematic I based the pcb off of. I've omitted the zeners for now.


pvision

Re: First PCB Layout
« Reply #6 on: April 27, 2018, 07:11:26 PM »
I'm getting 48v on the output to the mic pre. I'm not sure why though. Any thoughts?

You're measuring at the input not the output?

Nick Froome

Re: First PCB Layout
« Reply #7 on: April 28, 2018, 12:03:36 AM »
You're measuring at the input not the output?

Nick Froome

Ha, if only.
Measuring on the mic pre side behind the 22uf cap. ~48vdc between each leg and ground.

ruffrecords

Re: First PCB Layout
« Reply #8 on: April 28, 2018, 04:14:18 AM »
On your PCB layout I do not see a connection between XLR pin 1 and the output connector.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: First PCB Layout
« Reply #9 on: April 28, 2018, 01:58:33 PM »
I used the bottom ground plane to tie pin 1 to the power gnd. Is that bad practice? I’m kind of baffled by this. Its such a simple circuit without the diodes but there’s +48 on both sides of the blocking caps. :-\


ruffrecords

Re: First PCB Layout
« Reply #10 on: April 28, 2018, 03:22:52 PM »
I used the bottom ground plane to tie pin 1 to the power gnd. Is that bad practice? I’m kind of baffled by this. Its such a simple circuit without the diodes but there’s +48 on both sides of the blocking caps. :-\

For general grounding goo practice check this out:

https://groupdiy.com/index.php?topic=68869.0

Without the diodes the is no dc path for the caps to charge up through so the voltage across the cap will remain zero so both sides will be at 48V. Connect resistors from the output side of each cap to ground and they will charge up. Make them quite large, say 47K, so the do not load the input and you will see the caps charge up and the output side will drop down to 0V.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: First PCB Layout
« Reply #11 on: April 29, 2018, 06:07:03 PM »
For general grounding goo practice check this out:

https://groupdiy.com/index.php?topic=68869.0

Without the diodes the is no dc path for the caps to charge up through so the voltage across the cap will remain zero so both sides will be at 48V. Connect resistors from the output side of each cap to ground and they will charge up. Make them quite large, say 47K, so the do not load the input and you will see the caps charge up and the output side will drop down to 0V.

Cheers

Ian

Oh duh! Here I am looking at the pcb for an issue. Thanks for you help. That's why this forum rocks.


boji

Re: First PCB Layout
« Reply #12 on: May 01, 2018, 03:56:59 PM »
"That's why this forum rocks. "   It's like a handful of extremely competent and generous people that do 95% of the heavy lifting.  I feel somewhat compelled to start a patron page they can dip into at will.  I wouldn't have a clue how to enforce fairness or funds withdraw criteria...


 

Related Topics

  Subject / Started by Replies Last post
10 Replies
2539 Views
Last post July 20, 2008, 12:09:43 PM
by kato
2 Replies
1657 Views
Last post January 18, 2010, 04:00:37 PM
by oilcanstudios
69 Replies
10512 Views
Last post August 06, 2011, 04:55:20 PM
by Speedskater
5 Replies
1381 Views
Last post April 01, 2013, 06:05:05 AM
by ramshackles