Project: Silk Purse Page 2

The stock screws in the fiddles I've taken apart all have a long 'shank' area below the head and before the threads start. This would be fine if they were screwed into something that had a countersink area and then 1-1.5mm of plastic to go through but instead the shank sticks down into the wood and messes up most of the area that should be threaded. Mostly this applies to the screws on the back, the ones under the bridge we already removed.

The brass screw on the left is the original. the one next to it with no shank is one I found in an old-timey hardware store. Grips a bunch better and you can put it in and take it out more than once. You still need a very light touch, holding the screwdriver shank only between the fingers.

Update: Mar.24th   A Pig in a Poke: The Silk Purse's Pickup is not what it seems.

I've been around discussions about how the Piezo pickups work, and assuming that these cheap Chinese Piezo's were a single bit of PZT Piezo material all the way across under both feet, leading to a bunch of detrimental cancellation effects - etc. But did anyone actually take one apart to find out?
I couldn't find such a post. Since I like tearing things apart I got out the trusty Xacto knife and had a go at it. Fortunately for you I had the camera along.

Here's the pickup strip from my second violin (the one with baritone pretensions) You can't really see it here but there is a small black mark above the UR symbol on the left side. Note that the overlapped bit of shrink-tubing is on the right side. This will be important later.

Here's the first cut along the side. The silver thingy is the actual piezo element which slipped out after the first cut was done. Not glued or attached but just held in place by the shrink-tubing.

Here it is after all the shrink-tubing is sliced away. You can see the circuit board with the wires attached, the copper strip from the bottom (not so copper colored in this picture) The silver/aluminized bit that is the pickup element itself and the bit of brass plate that was filling in on the other side of the pickup. 
Yes you read right, this is a single sided pickup unit. "Are they all that way?" I have no idea, I assume so, at least for this product line. 

The bottom of the mini-circuit-board above, forms one part of the pickup 'sandwich'.
The two sides connect to the two wires that lead back to the connector plug. The longer side with the two holes was where the brass plate lived. It is also the side of the circuit that connects to the shielding layer on the other side of the board and the shank (ground) on the plug.
The other (smaller) end is where the pickiup element lives. The other side of the pickup element contacts the copper strip and completes the circuit through the copper strip and brass plate. FYI, there was no polarity marking on the piezo element itself.

I put it back together using clear shrink-tubing. Easier to see which end is which. That's Important.

So, It's really a single-sided pickup after all. The BIG question now is "Which side is the pickup on MY violin?". Ah, now that's an interesting question. The mystery continues...

On all these pickups I've seen, you can clearly see that one bit of the shrink-tubing overlaps the other, lets call this the overlap and the other end the underlap.  You can see the overlapping part even when you're just looking at it under the bridge between the feet.
In the one above, there was a dark mark on the bottom of the underlap side.  Note that the pickup itself lived in the overlap end. So in this case the mark is on the non-pickup end.
On my first violin of this type, the pickup was hanging out of the bridge base (since they arrive without the bridge installed) and it had a white dot on the top of one end. I put that end on the 'e' side of the bridge. Looking at it now the dotted end is the overlap end. If we assume the overlap end has the pickup in it, then I have the piezo element under the 'e' side on that instrument. If we assume that the dot 'rules' (though there was no white dot on this one) then I have the piezo on the 'g' (good) side. [Actually the 'c' side on this violin]

Augh, which is it. How do we know? Will civilization survive? Tune in Next Time for a thrilling conclusion...  No really, I don't know the answer, I'm going to take my other violin apart enough to get at the pickup and carefully slice the end of the shrink-tubing off on what I hope is the 'brass' end and have a look.

Edit: I've now had four of these apart. There is NOT always an indicator on the pickup that indicates which end of the pickup strip has the actual pickup element in it. One came from the factory with the element on the 'E' string end, one I'm not sure about and two had the element on the correct (IMHO) 'G' string side.  As suggested by others, if you gently lift up the pickup strip and touch it with your fingers while listening through headphones you can consistently tell which end is which. The 'hot' end has much more high frequency content and is louder when touched. 

Some clever work by Barry in Melbourne with his handy oscilloscope showed that the best, most even frequency distribution (electrically speaking at least) comes from having two pickups, one under each foot and wired out of phase. Fear not though, he also showed that having a single pickup (like we have here) under the lower frequency bridge foot G (or C) side is almost as good. We assume it's because the higher energy content on the 'E' side actually balances fairly well with what comes directly down from the lower frequency side of the bridge. That said we don't have this completely figured out. What we do know: Putting the pickup under the 'E' side sounds pretty screechy and awful. Yuck. Anyway, have fun out there!

Continued on later post: