Another E/V 664 Thread

[floid]

recently bought a "cut wire special" e/v 664 on evilbay, hoping someone had simply reclaimed their cord for other purposes. But alas and alack, such was not the case: after coming up with a cord solution of my own, I plugged into my most basic pre and said hello before even bringing up any monitoring: I saw one brief "signal present" flash of LED green and nothing more. Digging into the capsule, I quickly found out why: the leads from the voice coil were completely corroded, apparently all it had taken was that one little puff of air to turn them to dust.
Anyway, I dug in and decided to see what I could do. Razored the diaphragm off the motor assembly, made a complete mess of my attempts to gently remove remains of said coil... and then started taking pictures.
The motor assembly on these guys is pretty cool - one thing to read about the porting system E/V came up with, another to actually see it:





Next I started winding coils - tricky stuff, coming up with how to devise a properly sized form that I could also remove my work from. I ended up using a coke can (marking "roll to" seam based on my best approximation of pi times D), around which I rolled a few cigarette papers - I used OCB (aka "old coot's brand") because they are slick and gumless.
here are a couple of my attempts:


I used the wire from an old pickup. It was thinner than the original wire, so I had to kind of make up how many turns I should wind - the original, as near as I could tell once I unraveled the tangle and measured the various bits of it, was roughly 33 turns: a single layer down, single layer up arrangement. There's math you can do that will give a turns figure for a different gauge, but I had no way to gauge my wire and was flying in the dark. I tried a 66 turn and found it was too thick for the gap. So for my last wind, I did a 51 turn and a 35 turn. I ended up using the 51 turn, it measures 15 ohms/2.2mH on my probably not so accurate meter.

I pushed the turns off the coke can form,

and slowly worked them off the papers. I'd put a really thin coat of superglue on to hold them together, but they still came undone a little. used a slightly undersized socket for final forming

the goal being to have the coil sit evenly in the gap

I never did get it quite perfect, but for fingers and tweezers, it was as good as I thought I could achieve. glued it to the diaphragm and diaphragm to motor


and did final reassembly:







here it is in action, with a 57 for comparison.

and here is a soundclip
http://www16.zippyshare.com/v/88656670/file.html
664 on left, 57 on right, identical settings on my MPA Gold with no further processing. If you listen, you can hear the rub, and it's definitely not as articulate as the 57... still, hey, I replaced a freakin voice coil in the beast, y'know?

[vvv]

Very, very !!!

Look like yours came apart easier than mine; I hadda stick a screwdriver in the side screen (twice) and press it forward to lever the guts out - the whole thing came out as one piece, stuck together.

[The Scum]

Dang. That's pretty impressive. I don't know that I'd have thought to try it myself!

A couple of things occur to me:

For the coil forming, you could set up the coil former tube somewhat more empirically if you were able to actually roll it up and stick it into the gap, then remove it and collapse it a tiny bit more.

If you were able to collapse it even further once the coil was formed, then the coil would slide right off. Maybe with a hose clamp?

I find Superglue is hard to work with. Clear fingernail polish might be useful...you can dilute it with acetone so it flows easily, to get a thin and even coat.

[floid]

yeah, creating the form for the coil is definitely the tricky business. My solution's major flaw was that I still had to bring the coil into round afterwards. As for sizing, it was actually a bit more than what I describe in the original post: using a rule with 1/64 inch increments, I did my best calculation of inner and outer diameters of the gap. This gave me a spread of circumferences to work within, and i'd roll my form, wrap a few turns of a thicker gauge wire around it, slide them off and check how they gapped... then roll my form a few 64ths larger and repeat until I'd found the right size. but it now occurs to me that I could have done as you suggest, and slid a rolled up piece of paper in there to get the size...
Superglue is definitely not the best stuff for this work - see the slop I left on the diaphragm. I actually have a jar of inductor enamel somewhere, but couldn't find it and just powered through with what I could find. Which is typical - whenever I take on something like this I tend to just dive in and bullshit my way thru it, then afterwards analyze what I should have done different.
So, anyone got a stack of spare diaphragms?

[The Scum]

My granddad used to do trim carpentry, and would do it largely without measuring anything with a tape. He'd simply lay the pieces into place, mark them with a pencil, then cut in a (manual) mitre box. He used crows-foot marks the tell him which side of the pencil line to cut to.

I try to apply that lesson in other domains - sometimes it's easier to make a temporary piece that fits just right, than it is to make a tedious measurement. That's where the "put something in the gap" idea came from.

On the other hand, there are some import digital calipers around now that are absolutely excellent for the money...about $20 a set.

[themagicmanmdt]

i'm proud of you. just saying.

love,

dad

[themagicmanmdt]

..?