DIY Pick up testing

[okabass]

Testing a bass PU. Try to get single coil sound and size. And humbuckers no-noise.
https://www.dropbox.com/s/kltt7ddgms....56-1.jpg?dl=0

The frame is a cheap China rail PU (series, 2x 5,5 kΩ, around 5 H). Magnet is now Alnico bar, 300 Gs. I have stronger caramic too, 800 Gs. Self made soft iron rails. Idea for asymmetric rails is from a Yamaha patent.

Not bad, but needs trimming.Perhaps parallel connected coils, but that could be too weak (around 2,8 kΩ).
Any Tips?

[Helmholtz]

Does it sound enough "single coil"? It still has two coils albeit with different local sensitivities. Higher Gauss at the tops of the rails will reduce effective aperture lenght and thus improve high frequency response, though I am not sure if this has much effect in a bass where the wavelengths of harmonics are relatively long.

I would use small stacks of thin insulated transformer laminations (silicon steel) for the blades. These conduct flux better than low carbon steel and reduce eddy current losses.

What do you want to improve?

[rjb]

The asymmetric rails certainly look cool. I'd be interested to know if you still have the original unmodified rails, and whether you think that an A/B test between the pickup with the original rails vs the DIY rails shows a difference worth the effort of fabricating the new rails. (IMHO, some narrow aperture humbuckers already get pretty close to "single coil sound" without modification.)

Wiring the coils in parallel shouldn't be a problem. You could use a DPDT switch (toggle switch or push-pull pot) to get both series and parallel options. Your pickup's DCR is very close to that of a DiMarzio Model P (listed as 11.54K with coils in series), and people have been using those things with serial/parallel switches since 1977. I would expect the parallel position to sound very bright.
http://www.dimarzio.com/sites/defaul...ams/ModelP.pdf

-rb

[Antigua]

Testing a bass PU. Try to get single coil sound and size. And humbuckers no-noise.
https://www.dropbox.com/s/kltt7ddgms....56-1.jpg?dl=0

The frame is a cheap China rail PU (series, 2x 5,5 kΩ, around 5 H). Magnet is now Alnico bar, 300 Gs. I have stronger caramic too, 800 Gs. Self made soft iron rails. Idea for asymmetric rails is from a Yamaha patent.

Not bad, but needs trimming.Perhaps parallel connected coils, but that could be too weak (around 2,8 kΩ).
Any Tips?

I know from looking at Seymour Duncan Vintage Rails that a single "rail" under the string mostly just serves to reduce the intensity of the magnetic field. The effect is not an easy thing to describe, but the attack tends to sound softer, and the decay is more natural. Think of the differences between AlNiCo 2 and AlNiCo 5, and that corresponds to the differences you get from reducing the intensity of the magnetic field. Using an AlNiCo bar instead of ceramic would further reduce the flux density.

If you play around with the Tillman comb filtering demo Guitar Pickup Response Demonstration you can see that the comb filtering with such a narrow aperture is very minimal. You shouldn't hear any difference between one rail or two, because the cancellations caused by the second coil will be of a very high frequency, beyond the operative range.

[David King]

Did I miss a sound clip in the Dropbox?

[Helmholtz]

I know from looking at Seymour Duncan Vintage Rails that a single "rail" under the string mostly just serves to reduce the intensity of the magnetic field. The effect is not an easy thing to describe, but the attack tends to sound softer, and the decay is more natural. Think of the differences between AlNiCo 2 and AlNiCo 5, and that corresponds to the differences you get from reducing the intensity of the magnetic field. Using an AlNiCo bar instead of ceramic would further reduce the flux density.

This is one of the effects that don't show in frequency response graphs and make listening tests indispensable. It is most probably caused by the nonlinear magnetization behaviour of the ferromagnetic strings in combination with a broadening of the aperture by the low magnetic field.

[rjb]

... thus improve high frequency response, though I am not sure if this has much effect in a bass where the wavelengths of harmonics are relatively long.

Some bassists prefer hi-fi pickups and amps with wide frequency response- I believe to reproduce percussive transients like string attack, popping & slapping, etc.

I would use small stacks of thin insulated transformer laminations (silicon steel) for the blades. These conduct flux better than low carbon steel and reduce eddy current losses.

From a more mundane perspective, unplated & uncovered mild steel will rust in a heartbeat.

-rb

[Helmholtz]

From a more mundane perspective, unplated & uncovered mild steel will rust in a heartbeat.

This applies to all non-stainless steel types. Common countermeasures are varnishing up to e.g. nickel or chrome plating as used in industrial humbucker poles. But this is a prototype.

[Antigua]

This is one of the effects that don't show in frequency response graphs and make listening tests indispensable. It is most probably caused by the nonlinear magnetization behaviour of the ferromagnetic strings in combination with a broadening of the aperture by the low magnetic field.

It's a given that response plots only speak to the RLC filtering of the pickup, and not the physical filtering.

Even listening test fall short when it comes to the effects of string pull, because, there are inconsistencies when it comes to setting the height of the pickup, or A/B comparing pickups of different magnetic strengths, since it's tedious or impossible to change the magnets in a pickup. Listening tests give a rough idea, but they do not constitute a rigorous or objective analysis. More research is needed to satisfy the many reasonable questions that can be asked about magnetic strength in relation to the strings. Manfred Zollner and took a crack at it in PotEG, but his testing was limited in scope.

I have also performed tests analyzing harmonic content with relation to string pull with 3 dimensional FFT analysis, and found some interesting things, but it's a subject that still requires a lot study to fully explain. For example, I found that added string pull causes energy to shift into different harmonic levels, in the same sort of way that touching over the 12th fret shift energy from the fundamental to the 2nd harmonic. A similar thing happens when the magnets pull upon the strings with sufficient force, and it the exact effect depends on where the pickup is located along the string, and how strong the pull is. An increase in beating can also be seen and specific harmonics, again depending on the amount of pull and the location of the pull.

Regarding the subject of aperture width, according to Tillman, the pickup in question is too narrow for the width to have an audible impact. I trust Tillman's reasoning, and so I think a listening test in that regard might just lead a person to believe they hear a difference that doesn't exist.

[bbsailor]

Another thing to consider.

Research, by a web search, the effect that Fender Jazz Bass and other dual pole pieces per string had on the sound of the bass. This applies to guitars also. If you move the string initially horizontally you may stimulate more second harmonics especially if your string is located in the center of two pole pieces and each time the string hits either pole piece, a signal is induced in the coil. So, in one horizontal cycle you have two pulses and a stronger second harmonic.

Descriptions of the Fender Jazz Bass indicate the it was brighter than the single pole per string pickup which has a stronger lower fundamental frequency.

Consider the different sounds from:
1. A blade pole piece
2. A single pole per string pole piece.
3. Two pole pieces per string.

These are a new set of variables to consider in your analysis of pickup design and have easily measurable audible consequences of the above three pickup design variants.

The simple test is to pinch the string with your fingers right over the pole piece or pieces, pull sideways about .125 inch, release and note the wave form and harmonics in the initial transient for each of the three pickup pole variants.

Tinkering is a great way to learn!

Joseph J. Rogowski

[okabass]

Thank you all for interest and great advice. I think thread may be too long and heavy if I answer each one.
I haven't said it exactly but my goal is to make a noisless PU, which has the size and character of the original P Bass single c. PU. If it has a bit thicker sound thats ok.

Last night I tried the PU at rehearsals and it works surprisingly well. Single coil sound is quite credible. I have to match better the polepiece heights. I may try narrower polepieces, because P Bass single coil has ca. 5 mm PP. Now it has ca. 7 mm PP.

[okabass]

Another thing to consider.

Research, by a web search, the effect that Fender Jazz Bass and other dual pole pieces per string had on the sound of the bass. So, in one horizontal cycle you have two pulses and a stronger second harmonic...

Descriptions of the Fender Jazz Bass indicate the it was brighter than the single pole per string pickup which has a stronger lower fundamental frequency.

Joseph J. Rogowski

How do think it works, if I cut for example a 1-2 mm slot to the poles?

[bbsailor]

How do think it works, if I cut for example a 1-2 mm slot to the poles?

Observe the pole spacing of the Jazz Bass pickups. They are all about equal the the thickness of the low E string. The trade off is minimizing magnetic pull when the pickups are close to the string and getting a balanced sound from all the strings. You may want to consider spacing the magnets closer together for the higher bass strings while accurately having each string exactly in the center of each magnet pair. This is a case where experimenting with the physical layout of the magnet spacing and string diameter may yield some unique ways to balance the sounds of the strings better than keeping all string pole pairs the same spacing. Let your ears be your guide.

I do do not think putting slots in poles will be as efficient as having separate pole pairs per string.

Joseph J. Rogowski

[Helmholtz]

Even listening test fall short when it comes to the effects of string pull, because, there are inconsistencies when it comes to setting the height of the pickup, or A/B comparing pickups of different magnetic strengths, since it's tedious or impossible to change the magnets in a pickup.

What counts in the end is listening results. I love measuring and I am convinced that in principle everything that determines sound perception can be measured. It would be great to have objective measuring methods that can precisely predict PU sound. But the methods I know of only partially achieve this goal.

Manfred Zollner and took a crack at it in PotEG, but his testing was limited in scope.

You might want to read all 600 pages of volume 1 of PotEG before final evaluation.

Regarding the subject of aperture width, according to Tillman, the pickup in question is too narrow for the width to have an audible impact. I trust Tillman's reasoning, and so I think a listening test in that regard might just lead a person to believe they hear a difference that doesn't exist.

As already indicated, I doubt that aperture is an issue in this case.

But using transformer laminations can increase available flux.

[okabass]

I've listen and made some small changes. Like cut the poles a bit lover and more narrow. It had a bit too much high end (finger noise). I waxed it because the rails in the coilframes were too microphonic. I remembered me wrong the inductance (5H). It is 3,1 H, which is quite good for SCPB pickup.
It has good feisty attack and certain clarity and not too much bass end which are characteristic for '51 P Bass.
Must clean the PU more.
https://www.dropbox.com/s/axzj5bhonb....50-1.jpg?dl=0

I'm actually quite satisfied, and a bit surprised how nice the PU sounds. But must listen and make modifications when needed.

I'd like to thank all very knowledgeable advises.