[morsel]

PPA layout v0033 and schematic v0030 is our final release candidate. The deadline for posting comments, suggestions, and requests is midnight Sunday, July 20, 2003.

After any last issues are addressed, a final prototype will be ordered and validated, followed by a production run of boards. This process will take several weeks, as each order can take up to 2 weeks.

View the layout and schematic at http://elvencraft.com/ppa/

For more info see the original PPA thread

Changes since v30:

switched to heavy duty LED pads that accept 22 gauge wire and stouter LED leads
the LED trace cuts a cleaner line past the C1 caps
added missing labels
added a second set of rear input pads
added 3 #4 screw holes with 1/2 inch spacing

The new screw holes allow a daughterboard with 1/2 or 1 inch hole spacing to be mounted on the PPA. Tangent will make compatible crossfeed boards.

 

[guzzler]

does a #4 equal an M3 (3mm) hole in metric terms... if not, 3mm would be IMO the best choice as M3 nuts and bolts are the most widely used and very cheap!

g

 

[doobooloo]

So how will crossfeed be implemented in the PPA?

 

[Squalish]

Looks like a daughterboard right now, but I'm curious if they could fit the resistors for it in the lower 1" of the board(something that low profile wouldn't cause trouble w/ the switches, no?), and the taller caps right below the left channel buffers.

 

[eric343]

Is there a reason the -input and v+ pins of the opamps are swapped?

Just kidding. Looks great, guys!

 

[morsel]

Heehee, you made me smile, Eric.

Guzzler, the USA as you probably know is not a metric country. Since it created the electronic industry, many electronic standards are not metric, 100 mil pin spacing, for example. I believe the American screw standard is SAE (Society of Automotive Engineers).

The #4 screw hole on the board is 110 mils or 2.79 mm. The actual screw diameter is 112 mils. The next largest available hole size is 125 mils, or 3.175 mm. Tangent OKed the hole size since he is in charge of such mechanical things. I assume he checked this out and has good reasons for it as is, but perhaps he will comment for us. Clearly it is easier to ream a hole than make it smaller, but better yet to be the right size to begin with. I will guess that the #4 screw probably mates with common standoffs available from Digikey.

Squalish, there is no way we are putting crossfeed on the PPA board, sorry. It is difficult to implement without compromising the amp when it is bypassed, there is no room, and we have a perfectly reasonable daughterboard option.

Tangent's crossfeed board will attach to the PPA with #4 screws and standoffs through two of the 3 holes, 1-2 or 2-3, your choice. You wire the panel input jacks to the crossfeed, and the crossfeed to the amp inputs and crossfeed switch.

 

[binary_digit]

The PPA is not made with crossfeed in mind at all. The addition of crossfeed was there to allow others the ability to add it if they so choose. The addition of daughter board mounting holes is a request made by Tangent for the benefit of those in the DIY community that prefer such things. The crossfeed implementation is not associated with PPL and his design.

 

[morsel]

The PPA design was a team effort, bd. It was always our intention to provide a daughterboard interface.

 

[Squalish]

The meta42 board has extended pads w/ several holes each for different-size caps. Since it won't really make a difference in most cases if one doesn't use them, how about adding a few extra holes for convenience where it won't bother anything?

Another thing, if you wanted to make extra mounting holes in the middle, you have the space if you move some traces:

 

[Squalish]

Also, if you are interested in optimizing the layout a bit(if you want to fit extra features on in a future run or anything), you could make the trace from R13 to pin 4 of BUF3 go through pin 7 instead of around the IC. The red trace on R12 could be turned blue and put through pin 6 of the IC, saving a few moremils of space(as if it matters

) Of course, if you have concerns w/ stray inductence from the through-holes or whatchamacallit, then this doesn't apply.

I don't see any reason why the SOIC pads for the opamp need to be on the bottom, the top would seem to be more convenient.

Can't think of anything else, just want to say nice work, looking forward to making one at some point in the future.

 

[morsel]

The reason the so8 pads are on the under side of the board is because mirror image superimposition allows the traces to route without having to wrap around the outside of the DIP pins, which would be the case if the so8 pads were on the top side. Try it yourself and see what a mess it makes.

The circle around the mounting hole is the no fly zone for the standoff, nut, and/or screw head. The gif you attached shows that line crossing a pad that allows for dip socketing resistors. Also, I don't think the hole spacing you used matches the existing holes. In any case, the existing mounting holes should do the job. It's a bit late to be altering the core of the amp layout just to accommodate extra mounting holes.

Can you give any specific examples of caps you want to use, including the brand, model number, dimensions, lead spacing, and PPA part name?

 

[tangent]

Quote:

does a #4 equal an M3 (3mm) hole in metric terms... if not, 3mm would be IMO the best choice as M3 nuts and bolts are the most widely used and very cheap!

Which part of the screw is 3mm? The shank, or the thread diameter, or the desired hole size, or...?

Have you tried these screws in the META42 board's crossfeed mounting holes? These are the same size holes as we're currently using on the PPA board. The crossfeed mounting holes have been on the META42 since November and I have heard no complaints about it so far.

Quote:

The actual screw diameter is 112 mils.

The ones I have are 108 mils. Due to tolerance issues, the holes can be as small as 106 mils, and I just measured one here that is indeed that size. A 108 mil screw goes in without trouble: a bit of friction, but no real force involved. It's not like I pushed the hole plating out of the hole or cut new threads in its wall. 2 mils is about half the thickness of a piece of printer paper.

Even if cutting new threads in the plating wall or ripping the plating out entirely were necessary, this isn't a problem. The holes are plated because that's an automatic part of the manufacturing process, not because we want them to be plated.

What really matters here is the diameter of your screw heads. Right now, we're budgeting 250 mils. If you use screw heads larger than this, they may collide with something nearby.

 

[Neophyte]

Just my 2 cents.. But is would be sort of cool if the cross feed board had the ability to plug into the PPA like a video card would into slots in the PC. That would sure clean up a lot of wire! an simple jumpers could be added to the PPA for those who wish to not use the cross feed jack.....
AS I said jsut my 2 cents...

 

[Squalish]

Okay, I think I see what you mean w/ the superimposition thing.

The cap pads - I don't really have suggestions, just observed that about the META42, and thought that it would be nice. Add another hole or two 100mils closer and farther away from the center of each cap outline, and IMO it would be a little more modular.

</end "my attempt at giving the PPA a taste of my signature Krazy Layout">

 

[Chipko]

M3 means that the whole is 3mm, the screw is marginally smaller, I think a nut is about 6mm at its widest point. I don't have a standards reference here so I can't verify it.