Single Formvar vs. Poly

[fieldwrangler]

Folks -

So it seems, I wound some prototype pickups with some 44 single Formvar I had lying around from the early 80's and they sounded just the way I wanted. So, in the service of starting a short run I wound some others with 44 Poly and they sound really, really different; sort of like I threw a cap across the output. The high end got closed & tired sounding.

As closely as I can approximate a mic'd reading of the wires, the Formvar measure .0022 and the Poly .0021.

There are some other differences between the pre-production versions and the 1st ones, but before we get into all that I wonder what the more learned & experienced folks think about the possible role of the wire change in this perceived effect...

Bob Palmieri

[big_teee]

Unless the wire is the same size and same ohms per foot, it would be hard to have a fair sound comparison!
I've noticed that most of the new poly wires are very small per gauge.
T

[David King]

But here's what's odd, if you used a finer wire this time around you'd expect a smaller coil for the same number of turns and that should yield a slightly brighter sounding coil, all else being equal. I suspect you have some internal shorts which is having the effect of loading the coil down with eddy currents and causing it to sound dull. Are your DCR measurements pretty close? It could easily be something else entirely.

[Joe Gwinn]

Assuming no shorts, the effect may simply be due to differences in the thickness of the insulating varnish coating, independent of the diameter of the bare copper wire within.

This can be difficult to measure accurately with a micrometer not intended for such things, but the simplest way is to take a sample, strip the varnish from a few inches of wire using paint stripper (not mechanical scraping or burning), measure the two diameters to 0.0001", subtract, and divide the difference by two to get the approximate insulation thickness.

If one has an LCR meter, one can also compare the thickness by measuring the capacitance of a bundle of wire submerged in a pool of salt water held in a metal cup. One measures between wire metal and the cup. (Ordinary capacitance meters in DMMs may not be accurate because of the resistance of the salt water.) Given the length of wire used to make the bundle, one can compute capacitance per meter. Do this twice, once for the Formvar, and once again using poly.

Also, with a LCR meter, one can tell if the coil is shorted.

[Mark Hammer]

You raise an interesting side-topic...at least interesting to me.

Just exactly what serves as a usable solvent for the various coatings found on magnet wire. A buddy who used to use ultra-thin formvar-coated electrodes for single-braincell recordings, back in the old days, would coat the wire with formvar, and then dip just the very end into something to dissolve the bit coating the very end. It was 30 years ago, so I don't remember what it was called, but I know it is possible.

So what can we use with what?

[fieldwrangler]

Assuming no shorts, the effect may simply be due to differences in the thickness of the insulating varnish coating, independent of the diameter of the bare copper wire within.

This was my first thought

This can be difficult to measure accurately with a micrometer not intended for such things, but the simplest way is to take a sample, strip the varnish from a few inches of wire using paint stripper (not mechanical scraping or burning), measure the two diameters to 0.0001", subtract, and divide the difference by two to get the approximate insulation thickness.

I've been wondering what the right chemical would be.

If one has an LCR meter, one can also compare the thickness by measuring the capacitance of a bundle of wire submerged in a pool of salt water held in a metal cup. One measures between wire metal and the cup. (Ordinary capacitance meters in DMMs may not be accurate because of the resistance of the salt water.) Given the length of wire used to make the bundle, one can compute capacitance per meter. Do this twice, once for the Formvar, and once again using poly.

This is a really cool thing that I never knew anything about before!

Bob Palmieri

[fieldwrangler]

You raise an interesting side-topic...at least interesting to me.

Just exactly what serves as a usable solvent for the various coatings found on magnet wire. A buddy who used to use ultra-thin formvar-coated electrodes for single-braincell recordings, back in the old days, would coat the wire with formvar, and then dip just the very end into something to dissolve the bit coating the very end. It was 30 years ago, so I don't remember what it was called, but I know it is possible.

So what can we use with what?

+1

[big_teee]

Measuring the ohms of 10 feet of wire per roll, will easily accomplish the same thing as stripping and measuring the bare wire.
The higher the ohms, the smaller the wire.
T

[fieldwrangler]

If possible, I plan to do all of this stuff.

In theory, as I understand it, the effects of interwinding capacitance should be small compared to the usual effects of the linkage that follows but I think I need to investigate this stuff for myself. For one thing, I'm gonna try winding the poly coil with much more scatter to see what that does.

[Lollar Jason]

Alot of variables- some you may not have thought of.
If you are using two different guitars to compare the pickups make sure the pots and caps are matched and wiring harnesses are the same- try swapping the pickups into the opposing guitar and see if the tone follows or not.
I found with smaller diameter wire like 44 the resistance bleeding off treble is much more noticeable than larger diameter wires. Hard to say without examining every variable.

[fieldwrangler]

Thanks, Jason. This thought has crossed my mind, although it's good to have someone put it back up front.

In this case, all of the pickups from the initial (Formvar) run sound excellent in numerous axes and all of the ones from the second (Poly) run sound tired, closed & dull.

You're right, 44 is certainly a sensitive source. I've fought the idea of using this stuff at all (despite liking many of the usual low-wind historically nice-sounding suspects) but everyone (literally) likes the 44 versions much better than the 43 ones (wound to equivalent measured inductances) in this particular design, which, like almost all of my stuff, has very unusual magnetics.

You're also right that there are a number of variables, and I'm sure that I'm ignoring some. As I said, the wire wasn't the only thing that changed but I wanted to get some takes from the group on this suspect before looking elsewhere.

[the great waldo]

Assuming no shorts, the effect may simply be due to differences in the thickness of the insulating varnish coating, independent of the diameter of the bare copper wire within.

This can be difficult to measure accurately with a micrometer not intended for such things, but the simplest way is to take a sample, strip the varnish from a few inches of wire using paint stripper (not mechanical scraping or burning), measure the two diameters to 0.0001", subtract, and divide the difference by two to get the approximate insulation thickness.

If one has an LCR meter, one can also compare the thickness by measuring the capacitance of a bundle of wire submerged in a pool of salt water held in a metal cup. One measures between wire metal and the cup. (Ordinary capacitance meters in DMMs may not be accurate because of the resistance of the salt water.) Given the length of wire used to make the bundle, one can compute capacitance per meter. Do this twice, once for the Formvar, and once again using poly.

Also, with a LCR meter, one can tell if the coil is shorted.

Hi Joe
How would an lcr meter show a short differently from a normal multimeter ?

Cheers

Andrew (never to old to learn)

[Joe Gwinn]

Hi Joe
How would an lcr meter show a short differently from a normal multimeter ?

Cheers

Andrew (never to old to learn)

By measuring the excess of AC resistance over DC resistance, this difference being the eddy-current load. A shorted turn will cause this difference to be unusually high - eddy currents are in effect a shorted turn, and vice versa.

In manufacturing, one records the AC and DC resistances, and the pickups with shorted coils will show up as outliers compared to their fellows.

[Joe Gwinn]

I've been wondering what the right chemical would be.

I would use the gel strippers containing methylene chloride and methyl alcohol (methanol). These are to be found in paint stores, and big-box retailers like Home Depot and Lowes paint depts. Some local hardware stores may also carry these.

This is a really cool thing that I never knew anything about before!

There was a thread some years ago on this method. Search for salt water and capacitance and stainless steel cup.

[Joe Gwinn]

Posting from 2012 on measuring magnet wire capacitance

My 2012 posting on measuring the capacitance per meter of magnet wire is at http://music-electronics-forum.com/t30489/#post272338