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Deepdark

Well-known member
Joined
May 19, 2013
Messages
1,321
Location
Quebec, Canada
Hi guys

Quick one for you. I'm drawing a board for a LA2A within Expresspcb. It's my first ever experience of pcb designing. I'm using a 2 layer board.

First thing first, I know all footprints, all writting and components should be on the top layer. But all the traces should be on the top or the bottom layer?

Secondly, I run the HT and heaters on the other layer. Is it ok to do this? Once completed, should I ground fill both side?

Third, If I use a 0.020 width traces for signal and 0.030 for HT and heaters, is it ok?

 
Deepdark said:
First thing first, I know all footprints, all writting and components should be on the top layer. But all the traces should be on the top or the bottom layer?

There aren't too many 'shoulds' with PCB design - every situation is different.  Components, writing, etc, can all be on one or both sides - whatever fits the design goals the best.

Deepdark said:
Secondly, I run the HT and heaters on the other layer. Is it ok to do this? Once completed, should I ground fill both side?

Same as above - with the exception that high voltage signal traces (generally) need wider spacing:  I tend to use 50 mils or larger.

Deepdark said:
Third, If I use a 0.020 width traces for signal and 0.030 for HT and heaters, is it ok?

Again, it depends.  ;D Trace width and spacing are functions of current flow/heating, and working signal voltages/slew rates.  For externally exposed layers, 10 mils per amp is a good rule of thumb.  Which means for bridging signals even 10 mils is overkill.  People like to put in incredibly thick traces for everything, but that can cause worse performance as it tends to force routing traces closer together.  All other things being equal, thin and separate can be better than thick and close, if currents are small.
 
thanks matador. I tend to leave as much space between traces as possible. 10 mils should be plenty enough, then, I don't think an la2a runs more than 30ma, so should be ok.

So now, getting back to my question regarding the ground fill. I put all traces on the top layer (exept HT and heaters). Once finished, I should put a ground fill on the top layer. At least, this is how I saw it on all pcb i've worked with.  Concerning the bottom layer, the one with ht and heaters, is it better to ground fill it, too, or I should leave it as it is, with just the ht and heaters traces?

One thing I try to catch. If the majority of my traces are on the top layer, including the gorund fill, when I'll solder the component on the bottom of the board, all ground connections will make contact with the top layer within vias, isn't it? I mean, the ground fill is on the top layer, and all component are to be solder on the bottom of the board, so the only way to hake contact between the component and the ground fill is within vias?
 
I'm not the most experienced pcb designer here but when I make tube designs I try to keep the heater traces on the top layer if it has to be on board and the HT and audio traces on the bottom but I use vias where ever I need to. I prefer to run off board heaters, at least for the first gain stage. I try not to run over HT, Audio, and heater traces unless I have to. It's never really 100% ideal and I think transformer placement matters a bit more than traces but it all depends on what you're working with. I keep audio, grounds, HT on the bottom layer. But don't feel overly restricted with your moves. Keep traces short, avoid wacky traces if you can, and if it works well and it does what you want then call it a win. I usually end up revising once or twice. Good luck! Post a screen shot if you want to and some of the more skilled guys on here might be kind enough to give it a quick once over. I recently learned a lot by doing that.
 
Thanks buildafriend :)

Really good advices. I think I'll switch all my audio traces on the bottom layer :) For now, I plan mounting the transformers out of the board, including the power transformer (which will be installed outside the case). I don't know yet if I'll mount the tubes on the board or on the chassis. It will definitly reduce the pcb size wihtout the tubes on it. Anyway, it will reduce the build time just by having all the component on a pcb :)
 
You need to take great care with the 0V traces in order to achieve low noise and maintain stability. From where the 0V enters the PCB, it should first go to the output stage. From there it should go to the input stage and lastly to the input itself. You can make it a copper pour if you wish but is needs to follow the above scheme and it should not loop back on itself. This scheme ensures that output currents do not flow in input circuits.

Cheers

Ian
 
Thanks Ian. I should Run traces from each resistors and caps to ground instead of doing a ground fill. For exemple, running a ground from each resistor/caps of the amp section to a star ground, the same for the power supply and one for each audio transformer?
 
also, I make all my corner at 45° instead of turnind at 90°. But I saw sometime peoples use rounded corner traces. Why? Is it possible to make them in expresspcb?

Also, if I put all my traces on one side of the pcb, should I ground fill the other layer or I could let it untouched? I plan making ground traces from each components instead of ground filling them. Why some design are made entirely with ground fill and others are made of ground traces?
 
That's what I read from some articles about pcb designing. It was better to turn with 2x 45° instead of an abrupt 90°, just like in sewage plumbing, where we always make our 90° with 2x 45° elbows (yes, I'm in plumbing hahaa)
 
I see I was too subtle.

You may want to have a look at the thread I linked, in particular this post: http://groupdiy.com/index.php?topic=47264.msg594221#msg594221 and the articles that are linked to from that post.

JD 'MythBusting' B.
 
damn haha. It's not like plumbing, then. ;)

So now, I'll make my traces 90°

I guess rounded turn be part of the myth, too?

Also, is there any factor other than current who dictate the width of the traces? For exemple, the HT traces of a la2a (350V, around 30ma) Should I run the traces 50mils width, 30, or 10 is ok, given the fact that up to 1 amp I can go with 10mils?
 
> rounded turn be part of the myth, too?

They are prettier.

In days when we laid-out PCB with sticky tape and dots, one of the sheet-of-dots makers had a sheet of quarter-round corners. Not all layout artists bought it, but you could tell who did.

I do not know if XYZ-PCB software has rounded corners.

They take more space on complex/dense boards. . . .  they were most fun on simple boards with few-leg parts.
 
> who dictate the width of the traces?

"Who" is the guy who has to etch the board. On my hand-layouts and kitchen etches, 0.050" was as thin as I dared. Even then I could have some problems. Modern factory PCB fabs can etch traces I could not see. So find out YOUR fab's rules and guidelines. They might do hair-line but at extra charge, stick with their basic "we can do this easily" guidelines.

Expect to be wrong. Fatter traces are a little harder to cut but a lot easier to solder bridges to.
 
Thanks PRR. Actually, I got around 50% of the board done. I'm making it on 2 layer. That way, I can really minimize the size of the board and the overall lenght of traces. I must say it's a lot of work to place components, connect them, move them, etc, etc,etc. It's really fun, thought. I know I didn't take the easier one to begin with (LA2A) lol. Once I'll finish drawing it, I'll post it to get some advice, see if I did my homework well :)
 
ruffrecords said:
You need to take great care with the 0V traces in order to achieve low noise and maintain stability. From where the 0V enters the PCB, it should first go to the output stage. From there it should go to the input stage and lastly to the input itself. You can make it a copper pour if you wish but is needs to follow the above scheme and it should not loop back on itself. This scheme ensures that output currents do not flow in input circuits.

Cheers

Ian

Thanks for this Ian, I read this at the perfect time.

Best,
-JP
 
Is it possible to partition the board layout into expresspcb? Exemple, if I made a design for a product which will include 3 boards, can I already partition my board into several one?
 
here is the pcb I'm working on. feel free to comment if there is something wrong, things I should make on another way, etc. It's a LA2A pcb, double layer with audio on top layer and HT and ground plane on bottom. I made 4 gnd plane (input, output, audio and psu). I didn't draw the heaters yet. I don'T know if I run in risk of some sort of hum/oscillation with heaters on board.

 

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