My new project...

[LyleCaldwell]

This is a preamp/mixer/boost thing that I'll post details on later.  But the nuts and bolts of where I'm at now might be interestingt to some here.

As I'm still missing three caps (typo on my part when ordering) until tomorrow, it's not all wired up (pots and jacks are disconnected, no LEDs).  But it's all drilled out and the main parts assembled.

You can see a few areas on the rear panel that will change for the second prototype and for the production pedals - esp the pushbutton switches which will be round (misordered some square ones that I used for this prototype), and the pushbutton and power jack holes will be neater (hard to balance leaving room around the power jack without showing space around the jack itself - I may cheap and put a black plastic washer inside).  But this will be functional for testing.

The top from the front:



The back panel:



The insides (a very snug fit - I have literally about a 1mm margin of error, and this is with a 1590DD[!]):

[JimRayden]

Lookin' great! Can't wait to see it all finished up! What's the finish fonna be like?

-------------
Jimbo

[LyleCaldwell]

Thanks.  The finish will be the Hammond factory black powdercoat with an adhesive clear vinyl sheet on top with labels and loggo (from a sign company in town).  This was the least expensive method available to me, as I'm trying to keep the pedal costs down - the parts involved are expensive enough, as is the labor without doing full finishing.  But it will still look good and be durable.

[dano12]

Very nice work on what looks like a tight squeeze. Trimmer pots in the back? Can't wait for details on the circuit itself!

[Peter Snowberg]

   NICE !!!  

[Joecool85]

I wanna see the schematic, I need a preamp for my lm3886 amp, this looks perfect!

[jrc4558]

($@%ing A, man!!!
How do people make such gorgeously fine double sided PCBs??? Teeeeach meeeeee!!!

[LyleCaldwell]

Very nice work on what looks like a tight squeeze. Trimmer pots in the back? Can't wait for details on the circuit itself!

Pushbutton switches (DPDT for series/parallel for the loop and 4PDT to allow acces to the loop without using the preamp -details that will make sense when I post the details of this pedal next week) and two power jacks - 2.5mm for the incoming 9vac and a 2.1mm for outgoing 9.6vdc (again, it will make sense next week).

[LyleCaldwell]

I wanna see the schematic, I need a preamp for my lm3886 amp, this looks perfect!

Stay tuned - this is in no way a "transparent" preamp.  Details soon.

[LyleCaldwell]

($@%ing A, man!!!
How do people make such gorgeously fine double sided PCBs??? Teeeeach meeeeee!!!

ExpressPCB and a lot of painstaking planning.

[LyleCaldwell]

Some lessons learned...

First, the pushbutton switches come out way too far.  This will be fixed on the production PCBs.  On that note,

Second, place switches on the board first if possible when planning the layout.  Very hard to move them later, as dozens of small traces have to be re-routed (grr).

Third, the power jacks don't exactly line up with the holes in the chassis because I used pads that are too large for the legs of the jacks.  So they moved around a bit in the holes when soldering.  I've since gone back and specified smaller holes for those power jacks, so on the production boards there will be very little variation, so they will line up with the chassis holes.

Fourth, countersink drill heads suck when they get old and dull.  Chatter chatter chatter and rough edges.

Fifth, there is a difference between a 47uf cap and a 4.7uf cap, even if it's two in the morning when you place the order.  One brainfart/typo on my part and now I have to wait another day for the correct (4.7uf) caps to arrive.

Sixth, I'm glad I intended this to be a "learner" prototype, as I'd be kicking myself if I had planned on this one coming out perfect.

[Peter Snowberg]

1st rule of prototyping... it's a proto so don't expect everything to be perfect. 

As Express PCB only gives you a few drill sizes, on your next proto board order you might want to consider adding a sample of each drill on the side. That makes it super easy to try parts out in the finished hole dimensions.

And finally, for your production run you may want to consider using a ground plane. It looks like you have some TO-220 regulators in there. "Pouring" a heatsink is really convenient.

[LyleCaldwell]

Peter,

Actually, ExpressPCB has a lot of drill sizes - you just have to make sure the ones used in the "component library" are actually correct.  For this board I used custom components with specified hole sizes, pad diameters, and distances all over the place.  But I forgot to check a few, and they bit me on the butt.

For example, I have long used a particular model of IC socket.  That model was recently replaced with a new ROHC compliant (or whatever part).  I forgot to double check, and sure enough, the new pins are slightly too large to fit in the component holes I had in my library.  So I updated that custom component for future boards, and will now double check everything (and this time, I mean it).

Ah, ground planes... unless it's a digital clocking device, etc, I'm not a fan of ground planes, and even then, only around the IC.  I much prefer a very directional "steered" ground path, with power ground separate from signal ground, joining only at the ground of the input, with no loops.

But going back to the "doh" list above, while I ordered TO-220 heatsinks and planned to use them, I forgot to leave enough horizontal space for them, so there's no room on the prototypes.  The total current draw of the circuit is less than 100ma, and the likely current draw (for an external DC pedal) on the LM317 will probably be 600ma or well under (depending on the pedal, but probably also in the 100ma - 300ma range), so I may not need the heatsinks.  The prototype will let me know.