[zammykoo]

Hi all,
 
This is my first attempt at laying out a PCB for the tube amp. Keep in mind I have absolutely no electronics background so there may be things I am not aware of functionality-wise, hence wanting feedback. I do realize that there are some blank spaces on the board, which I plan on readjusting and compact the components tighter. I also know that the board is a bit lopsided and also the left and right side could be mirrored. The board size does not matter because I will be building the enclosure from scratch as well.
 
I am following Dsavitsk's 12au7 schematic & BOM, much thanks to Doug for that. The drawing is created in ExpressPCB, most of the custom components were taken from datasheets and built by me. This design is a double-sided copper plate, which the ground plane is removed in the screenshots for clarity.
 
If there is anything glaring, please let me know. Any comments welcome!
 
Tam
 

 

[dsavitsk]

I did not check for correctness, but the layout is not too bad.  I might do things like make the tubes, fets, and jack/pot equidistant from the sides.  Also, add a ground pad to connect the pot body to ground, and add pads for measuring voltages. But, overall it looks pretty good for a first go.  I think it was Tangent who said, and I paraphrase, that you are done with a PCB when you have gone over it and that every possible change makes something worse -- that is, when your board is Pareto Optimal.

 

[zammykoo]

Thanks for your feedback, Doug. Yep, my plan is to get this board Pareto Optimal.
 
But in order to get there I have some questions for you (or anyone else) regarding some design modifications. I have been studying your 19j6 PCB design for quite some time and noticed a few things about it. In no particular order, see below:
 
1. Most of the traces seem much shorter in length, say compared to mine. I wish to make it shorter as well, but it as just a matter of rearranging the components. I'm sure having shorter traces makes the circuit more efficient because the current does not have to travel as far. But does it affect sound quality to have longer traces?
 
2. I have considered simplifying the top copper layer by moving some of the traces to the bottom layer.... but this will create breaks in the ground plane... making it less effective. I figured since you don't have many breaks in your ground plane, then it's probably not a good idea to do so.
 
3. I wish to make a wooden enclosure, where the top of the case will be much thicker than a pre-made metal cases. This means the current heatsinks in the BOM will not work well. Can I substitute it for the vertical mounted Wakefield 657-15ABP?
 
Thanks!
Tam

 

[zammykoo]

Here's a quick update for tonight before bed:
 
V2
(unfinished drawing, heatsinks need to be mounted onto vertical fets)

 

[kchapdaily]

looks good! are you going to send the design out to get made, or etch it yourself?

 

[zammykoo]

Heya thanks, I will be doing a one-off (or two) by etching it myself. I really have no desire to send it out to be produced. The main reason why I'm doing this the hard way is to keep my build clean and to learn the pcb software. 
 
Keep the comments coming!

 

[jdkJake]

I have learned that you want the resistors (r3/r9) tied to the gates of the MOSFETs (pin 1) as physically close as possible.

http://www.head-fi.org/forum/thread/506984/ehha-rev-a-interest-thread/1125#post_7187613

 

[zammykoo]

Quote:

I have learned that you want the resistors (r3/r9) tied to the gates of the MOSFETs (pin 1) as physically close as possible.

http://www.head-fi.org/forum/thread/506984/ehha-rev-a-interest-thread/1125#post_7187613

Good suggestion! Thanks jdkJake. I will try to reorganize the layout again tonight.
 
Do you see anything else glaring that I am not aware of?

 

[zammykoo]

So.... I have been going at the PCB revisions many many times since the last one I posted. I must have redone it like 10x but still not satisfied.
 
I figured I might as well take a short break from that and focus on the custom case. I threw this model together to get a sense of the case size in comparison to the pcb board size. I call it the....sandwich!
 

 

[kchapdaily]

great design work! what program did you use?

 

[pabbi1]

Kudos on you choice of wood. I just can't get around wood sides and mesh metal top and bottom for my builds (due to the heat of the designs), but I'll be curious how yours performs. As an aside, how do you plan to machine the top?
 
Great mockup in any case.

 

[zammykoo]

Thanks for the kind words guys,
 
@kchapdaily
I used google sketchup to build the model. Great free/simple software for quick mockups. Not to mention google has an online warehouse of user submitted models that you can download and use. (I found those tubes model there)
 
@pabbi1
Yep, seems like zebrano is everyone's favorite here. Luckily for me there's a hardwood supplier here in Houston that has it
 
Are you talking about the amp being so hot that you wanted the top to be mesh for ventilation? I'm sorry, maybe I'm not understanding your question. As far as machining the wood, I plan on using my brother's homebuilt CNC machine. He's been calibrating it recently so if I don't get a chance to use that I might just route it out by hand.

 

[kchapdaily]

google sketchup! great software! i used that to do rough designs of houses and other stuff in my cad class back in highschool. 
 
ive already built one starving student, the original simpler design. im going to be building the 12au7 version soon. 
im also going to be making my own case out of wood. i think im going to go with birdseye maple

 

[zammykoo]

That's a unique wood texture, just for kicks I wanted to see what birdseye maple looks like on my model

 

 

[kchapdaily]

thats awesome! looks great!

 
my uncle is a cabinet maker, he uses birdseye maple in some really nice tables, nightstands, etc. 
its been my favorite wood for a long time, plus i havent seen it used in headphone amps yet