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Thread: DIY Pick up testing

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    DIY Pick up testing

    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?

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    Last edited by okabass; 05-11-2018 at 10:07 AM.

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    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?

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    Last edited by Helmholtz; 05-11-2018 at 04:24 PM.

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    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

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    Last edited by rjb; 05-11-2018 at 03:57 PM.
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    Quote Originally Posted by okabass View Post
    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.

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    Did I miss a sound clip in the Dropbox?

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    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.

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    Last edited by Helmholtz; 05-11-2018 at 09:30 PM.

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    Quote Originally Posted by Helmholtz View Post
    ... 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.



    Quote Originally Posted by Helmholtz View Post
    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

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    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.

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    Quote Originally Posted by Helmholtz View Post
    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.

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    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

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    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.

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    Last edited by okabass; 05-12-2018 at 06:49 AM.

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    Quote Originally Posted by bbsailor View Post
    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?

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    Quote Originally Posted by okabass View Post
    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

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    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.

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    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.

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    Last edited by okabass; 05-12-2018 at 05:53 PM.

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    Quote Originally Posted by Helmholtz View Post
    You might want to read all 600 pages of volume 1 of PotEG before final evaluation.
    Your condescending tone is getting to be too much. First, I know that there are not 600 pages of 1200 total pages devoted to this subject. There are not even that many pages dedicated to the guitar pickups. Second, PotEG is in German, with small parts translated, and I have even worked on making translations myself which you can see here http://www.echoesofmars.com/zollner/idr/?page=1 . I have been in contact with Gitec about translating more of the book by capable translators. I do put real effort into this.

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    Last edited by Antigua; 05-12-2018 at 05:30 PM.

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    Quote Originally Posted by Antigua View Post
    Your condescending tone is getting to be too much. First, I know that there are not 600 pages of 1200 total pages devoted to this subject. There are not even that many pages dedicated to the guitar pickups. Second, PotEG is in German, with small parts translated, and I have even worked on making translations myself which you can see here http://www.echoesofmars.com/zollner/idr/?page=1 . I have been in contact with Gitec about translating more of the book by capable translators. I do put real effort into this.
    I said don't judge before you have read all.

    I am respectful to people who treat me respectfully.

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    Quote Originally Posted by okabass View Post
    ...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.
    Although I once met someone who owned an original Telecaster Precision bass, I never met the bass itself.
    Can you define the character you seek?

    Have you tried the unmodified pickup before swapping magnets and installing asymmetric rails?
    Speculating, calculating, and tinkering can be good clean fun- but it appears you may be seeking a solution to a problem you don't have.


    Quote Originally Posted by okabass View Post
    ...I have to match better the polepiece heights
    If the tone with the original rails happens to be OK, but the string-to-string output is unbalanced, you could simply notch the rails under the louder strings- in the manner of certain "Charlie Christian" style pickups. (Of course, you would then apply some kind of rust protection to the filed sections.)

    -rb

    PS- OOPS. I wrote this offline while #15 was posted. Congratulations!

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    Last edited by rjb; 05-12-2018 at 07:14 PM.
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    Quote Originally Posted by Helmholtz View Post
    I said don't judge before you have read all.

    I am respectful to people who treat me respectfully.
    Well it is German, and I don't speak German, so cut me some slack.

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    Quote Originally Posted by Helmholtz View Post
    I am respectful to people who treat me respectfully.
    Said the man with the short fuse .

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    Juan Manuel Fahey

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    Quote Originally Posted by J M Fahey View Post
    Said the man with the short fuse .
    Meaning what? In plain simple english, please.

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    Say, did you guys hear?
    Okabass made a nice-sounding pickup.

    -rb

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    Quote Originally Posted by rjb View Post
    Although I once met someone who owned an original Telecaster Precision bass, I never met the bass itself.
    Can you define the character you seek?

    Have you tried the unmodified pickup before swapping magnets and installing asymmetric rails?
    Speculating, calculating, and tinkering can be good clean fun- but it appears you may be seeking a solution to a problem you don't have.


    If the tone with the original rails happens to be OK, but the string-to-string output is unbalanced, you could simply notch the rails under the louder strings- in the manner of certain "Charlie Christian" style pickups. (Of course, you would then apply some kind of rust protection to the filed sections.)

    -rb

    PS- OOPS. I wrote this offline while #15 was posted. Congratulations!
    I naturally tried original type PU. (My friend has all original '56 P Bass) Several PUs as a matter of fact. At least a dozen single coils, wound from 5,7 kΩ to 9 kΩ, different magnets, different strength. Stack- and spit coil- types.

    The character is not easy to tell, cause the bass is surprisingly versatile. I like certain rawnes, originality compared to split coil P Bass. Keith Ferguson with Fabulous TB, Dusty Hill with ZZ Top, Stings P bass sound...
    As I said my goal: single coil sound, humbuckers "noise".
    I tried stack, split coil type Humbuckers. They sound kind of lame to me.
    I tried Dimarzio's Fast Track 1. That China rail PU. Then I found Seymour D. Vintage rails patent which has partly cut rails. I cut China PU's rails, but I feel it still has some "mud" . Then I found that Yamaha patent, with comb-type rails. I feel it is the best of the rail types I tried. But lets see...or listen.
    I potted the PU and put a vintage correct cotton string. Must clean it a bit some day.
    https://www.dropbox.com/s/axzj5bhonb....50-1.jpg?dl=0

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    Last edited by okabass; 05-12-2018 at 11:42 PM.

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    Quote Originally Posted by J M Fahey View Post
    Said the man with the short fuse .
    (Google knew the phrase)

    Thanks, will (re)consider.

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    Quote Originally Posted by okabass View Post
    How do think it works, if I cut for example a 1-2 mm slot to the poles?
    Probably no effect. What works is to laminate the pole blades: Instead of one mild steel sheet of say 2mm thickness, use two identical sheets of 1mm thickness, insulated from one another, and so on. Tune by ear.

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    Quote Originally Posted by Joe Gwinn View Post
    Probably no effect. What works is to laminate the pole blades: Instead of one mild steel sheet of say 2mm thickness, use two identical sheets of 1mm thickness, insulated from one another, and so on. Tune by ear.
    Now I 've been listening more, the high end could be more warm (add a little cap?). It has kind of sizzle. In what direction laminated blades will go? Part of the '51 PU's sound I like is kind of brutal attack because of single ca. 5mm magnet pole per string. I may try little screwheads as poles.

    Ps. Got a idea to use screws as pole pieces, to make it less sizzly. I tried with a 7ender bass PU screw and magnet bar only. I got ca. 300 Gs at the screw head. What do you think: is that too little.
    I checked some Gauss values, it is not very far from P-90 (Alnico II). Or PAF (Alnico II or V).

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    Last edited by okabass; 05-14-2018 at 05:21 AM.

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    What kind of control circuit do you use? Lower pot resistance values will reduce excessive highs.

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    Quote Originally Posted by Helmholtz View Post
    What kind of control circuit do you use? Lower pot resistance values will reduce excessive highs.
    Normal P Bass: 250 kΩ vol pot and tone. Very clever simple idea. Must try.

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    Quote Originally Posted by okabass View Post
    Normal P Bass: 250 kΩ vol pot and tone. Very clever simple idea. Must try.
    250k is about as low as you can reasonably go with off the shelf parts, so an alternative to forcing a lower Q would be a 500k trim pot, so that you can dial in some ideal amount of additional parallel resistance. Turning down the tone pot also lowers the Q, so this mod is roughly the same as forcing "8" or "9" to be the maximum tone setting, depeding on the value of resistance.

    If you wanted to see what was happening for certain, it's possible to see the resonant Q with a bode plotting oscilloscope, such as the Velleman PCSU200, or you can even create a model with LTSpice, which is free, plug in the values of the pickup and simulate different loads. That latter wouldn't model the eddy currents of different screws, but it would reveal the change you get with, say 250k versus 500k pots. If you've never done either of these things, there a learning curve involved, but it's worth knowing that trial and error isn't the only option available.

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    Quote Originally Posted by Antigua View Post
    250k is about as low as you can reasonably go with off the shelf parts, so an alternative to forcing a lower Q would be a 500k trim pot, so that you can dial in some ideal amount of additional parallel resistance. Turning down the tone pot also lowers the Q, so this mod is roughly the same as forcing "8" or "9" to be the maximum tone setting, depeding on the value of resistance.

    If you wanted to see what was happening for certain, it's possible to see the resonant Q with a bode plotting oscilloscope, such as the Velleman PCSU200, or you can even create a model with LTSpice, which is free, plug in the values of the pickup and simulate different loads. That latter wouldn't model the eddy currents of different screws, but it would reveal the change you get with, say 250k versus 500k pots. If you've never done either of these things, there a learning curve involved, but it's worth knowing that trial and error isn't the only option available.
    Agree!!!

    But, make sure you use a capacitor equal to the capacitance of your coax cable feeding your amp. Also, add a 1M ohm resistor in parallel with the pot to represent the amp input loading. This will get what you see on the Bode Plot closer to what you actually hear when plugged in to your amplifier.

    One interesting experiment is to build the Tillman active FET buffer located in the instrument end of the coax cable plug. This device puts from a 5M to 10M ohm input load on the pickup thus eliminating the effect of cable capacitance and reduces amp loading and requires no instrument mods as it is all external to the instrument. What you will hear is a brighter sound with a higher resonance and higher Q at the resonant frequency. Part of the experiment is to listen to what effect varying the volume pot has on the tone.

    Enjoy.

    Joseph J. Rogowski

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    Nice advices. Thank you.
    I've tried a DI box that has several Megs input, it gives indeed quite bright sound.
    I've listened and I have a conclusion that the sound has kind of piezo type not so nice nor warm sizzle. I have now a multicap switch in place of the tone pot. Cap values from 470 pF to 100 nF, and a 16 step switch. I'll listen with different caps. Perhaps I try the screws as a pole pieces.

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    I've got a troglodyte-level question:

    I'm guessing that the original blades are about 16Ga = 1/16" = .0625" ~= 1.6mm thick.
    And you are going to try replacing the blade with... perhaps fillister head humbucker screws with 5-40 or M3x0.5 threads, having major diameter of .125" or 3mm?
    Question: How thick is the plastic surrounding the blade; can you install the screws without damaging the coil?

    Grunt, eh, unga unga
    -rb

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  33. #33
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    Quote Originally Posted by okabass View Post
    Normal P Bass: 250 kΩ vol pot and tone. Very clever simple idea. Must try.
    Well, as you have a tone control, do you use it ? The simplest way to reduce resonance Q is to back the tone control a bit. Does this cure your problem?

    Sorry, just saw that Antigua recommended the same.

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  34. #34
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    Quote Originally Posted by rjb View Post
    I've got a troglodyte-level question:

    I'm guessing that the original blades are about 16Ga = 1/16" = .0625" ~= 1.6mm thick.
    And you are going to try replacing the blade with... perhaps fillister head humbucker screws with 5-40 or M3x0.5 threads, having major diameter of .125" or 3mm?
    Question: How thick is the plastic surrounding the blade; can you install the screws without damaging the coil?

    Grunt, eh, unga unga
    -rb
    I have a watchmakers education, I can work a bit with materials. I think I can joint the screw and the 1,6 mm blade.
    Here's a watch I've made.
    http://okabass.suntuubi.com/datafile...s/HPIM1265.JPG
    http://okabass.suntuubi.com/datafile...s/HPIM1262.JPG

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  35. #35
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    Hemholtz:
    Yes I tried tone control. I have now "multicap switch" instead of normal tone. I found it better than normal tone (250kΩ + 47 nF or 100 nF).
    Listening sounds are strange, now it sounds quite good with a fet bass preamp.

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    Last edited by okabass; 05-14-2018 at 11:35 PM.

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