Turns Per Layer

[Joe Gwinn]

I don't know if it matters, but looking at the analyzer plot, in the lower left corner, the large red sinewave is showing slope distortion on the back (right flank) of the negative peaks. This implies that the drive amplitude is too high for that frequency, and is causing an amplifier somewhere to become nonlinear, where the amp's max slew rate is insufficient to follow the signal. Asymmetrical slew rate limiting is common in operational amplifiers, so the fact that only the negative peaks are affected isn't surprising.

[David Schwab]

...the neck is all glossy nitro...

That's not going to affect the tone whatsoever.

[Mike Sulzer]

I don't know if it matters, but looking at the analyzer plot, in the lower left corner, the large red sinewave is showing slope distortion on the back (right flank) of the negative peaks. This implies that the drive amplitude is too high for that frequency, and is causing an amplifier somewhere to become nonlinear, where the amp's max slew rate is insufficient to follow the signal. Asymmetrical slew rate limiting is common in operational amplifiers, so the fact that only the negative peaks are affected isn't surprising.

That distortion occurs well away from where the the waveform should be changing the fastest. I think it is some other kind of distortion rather than slew rate limiting, although perhaps it could be if there is an instability involved as well. I also doubt that winding technique as described could make that much difference in the frequency response. That also indicates that there is something wrong with the measurements.

[RedHouse]

Funny thread.

Sounds like (many have) forgotten their early learning in winding-101 class, wasn't TPL like the very first thing a guy experiements with after gettting a machine up-n-running and buying a spool of wire?
(and writes it all down in their notebook for later reference)

[RedHouse]

(double post)

[Joe Gwinn]

That distortion occurs well away from where the the waveform should be changing the fastest. I think it is some other kind of distortion rather than slew rate limiting, although perhaps it could be if there is an instability involved as well. I also doubt that winding technique as described could make that much difference in the frequency response. That also indicates that there is something wrong with the measurements.

In practical opamps, slew rate limits depend on output swing, and the kind seen in the picture is common. While it's true that the max slew rate occurs around the center, this is a large-signal effect, so one must read opamp datasheets to know what exactly will happen. General theory won't be much help.

[Steve Conner]

Bear in mind that if the signal is being differentiated by the coil system (and from the frequency plots it looks like it is) then the slew rate distortion will appear at the peaks instead of the zero crossings.

[Jim Shine]

I hand wind. On humbuckers I shoot for 100 TPL and expect a 10% tolerance in that. I just try and hit that 100 mark as often as possible. That is the ballpark I like. My tension varies on the wire I am using. 42 PE, I tend to wind tight. 44 or smaller poly, I use a looser tension.

[Mike Sulzer]

In practical opamps, slew rate limits depend on output swing, and the kind seen in the picture is common. While it's true that the max slew rate occurs around the center, this is a large-signal effect, so one must read opamp datasheets to know what exactly will happen. General theory won't be much help.

Joe, I have been working with ic op amps for over 45 years, starting with the old Fairchild 709. I know what slew rate limiting looks like in theory and practice, and that doe not look like it. Furthermore, who would use an op amp that slew rate limits at 10 KHz considering what is available now? Such an engineer would be laughed out of the profession. Yes, there is a large signal effect there; that channel could be overloaded, as I believe the numbers indicate.

Slew rate limiting occurs because the gain of the second stage falls off with frequency resulting from the frequency compensation introduced by capacitance from the output to the input of the second stage. This increases the current the first stage must able to supply for full amp output as a function of increasing frequency The first stage is a fancy emitter coupled (or equivalent FET) stage. It has good linearity up to near the current limit. The triangleization of the sine wave is evident on every one I have examined (except in improperly compensated situations).

What I do not understand is why you decided it was slew rate limiting and now defend that. There is nothing there that indicates slew rate limiting.

[Mike Sulzer]

Bear in mind that if the signal is being differentiated by the coil system (and from the frequency plots it looks like it is) then the slew rate distortion will appear at the peaks instead of the zero crossings.

10 KHz is slightly above the resonance; the impedance should be quite high. If the circuit driving the coil is an op amp current source, it would be easy to exceed the voltage limit of the op amp.

[Joe Gwinn]

What I do not understand is why you decided it was slew rate limiting and now defend that. There is nothing there that indicates slew rate limiting.

Because it looks like it. Not having this bit of commercial gear on our lab benches, that's the best any of us can do.

[Mike Sulzer]

Because it looks like it. Not having this bit of commercial gear on our lab benches, that's the best any of us can do.

This shows slew rate limiting: RMAA Testing of Audio IC Op Amps

Scroll down most of the way. These test were done at 320 KHz with an output of about 3V peak. Only the ancient MC4858 (1.5 volts per microsec slew rate) shows a strong effect even at this high frequency. The others show more subtle straightening of the waveform.

[madialex]

Hi Guys, been a good while!! Hope all are well. In my observations and yes I hand wind but I have noticed something. Loose TPL and standard tension seems to darken the pickups. Tight TPL and tighter tension seems to me to brighten the pickups. I wound 2 buckers same turns on each one 4500 per coil, One was wound normal to loose tension with fast TPL say 45 to 65 the other was wound Slow tpl each layer tight against the other or as tight as I can get it hand winding and slightly higher tension and the difference is night and day, the latter was hands down brighter. I went so far as to increase the tension to just below stretching with the high TPL and it was even brighter but kinda sterile sounding. Was ok but really nothing to write home about. Hope this input helps the debate somewhat.

[madialex]

I always thought more scatter = less capacitance since each turn is farther apart? Less capacitance would make a brighter pickup.

Exactly! At least that's what I have found.