Single coil resistance

[slausonm]

I posted this request in the builder's forum, but no responses. I am a teacher. For the past few years we have been building insruments in a manufacturing class I teach. This years' instrument is an electric mandolin with a single coil pickup. It is a semi solid body design with an F styling. I wanted to introduce the students to electronics, so we are building our own single coil pickups. I am using alnico 5 magnets and 42awg magnet wire. 4 magnets, one for each pair of strings. So what is a good starting value for electrical resistance on a small instrument like this?

The bodies are made except for pocketing them for the pickup. I hope to have a prototype done over the thanksgiving break. I will post some pictures soon.
Thanks!
Matt

[Tom Wright]

Steve Ryder's stacked-single-coil pickups are around 7.5K ohms. Pete Mallinson of Almuse made a replacement single-coil for my cheap Fender acoustic-electric, which measures at 4.3K. That was a bit light in output/tone, should probably be more than 5K.

BTW, would be wise to make the A string magnet a bit short compared to the others. I find you can balance bronze wound strings fine if you can push up the poles for them and the E. The A is always strong, so if you start with it shorter the four poles can be nearly flush if wanted. Otherwise you will want the A recessed or the others higher.

Ryder used 500K pots on my old EM-45, and a 0.47 pF (478) capacitor on the tone pot.

[Soundfarmer Pete]

Around 5.5k is pretty popular.....although there are other things to take into account, a general rule of thumb is that the higher the resistance, the higher the output at the expense of even frequency response....the top end disappearing (the reason why Les Paul favoured low impedance pickups).
With 42AWG wire you`ll probably end up with quite a chunky pickup unless you go for a deep coil/magnet arrangement.
Here`s a link to a coil estimator....if you have a play with this, you might get a few ideas.
http://www.salvarsan.org/pickups/Coil_Estimator.html
Have Fun!!!

[Soundfarmer Pete]

QUOTE]
BTW, would be wise to make the A string magnet a bit short compared to the others. I find you can balance bronze wound strings fine if you can push up the poles for them and the E. The A is always strong, so if you start with it shorter the four poles can be nearly flush if wanted. Otherwise you will want the A recessed or the others higher.

QUOTE]
Good point Tom mentions about magnet length.....at least pickup parts suppliers usually have different lengths of magnet available (for those vintage staggered Strat pickups among other things).
Just wondering....are Steve Ryders pickups wound directly onto the magnets or onto a bobbin that isolates the windings from the magnets? Apparently, many old Fender pickups were trashed as a result of attempts to adjust the magnet height.

[Elliot Luber]

Hmm: "Single-Coil Resistance." Good name for an band.

[slausonm]

Thanks for the great responses. The tip on the A string magnet is much appreciated. I was thinking a starting point of 5K was probably good experimentally.

So tomorrow will be neck making day and possibly solid modeling the pickup parts to be cut in the laser. Turkey day will be picture posting day while the other's eat and watch football.

If you think of something else please let me know.
Thanks! Matt

[slausonm]

Hmm: "Single-Coil Resistance." Good name for an band.

Nice!

[slausonm]

If you are interested in my project here are some photos and video. It is essentially roughed out. But this will give you the idea of where I'm going.
The CNC router is a home build. A student cut the steel for me and helped me put it together. The machine is slow but pretty effective.

http://smg.photobucket.com/albums/08...lin/?start=all

Matt

[slausonm]

I made my first pickup this week. I designed the top and bottom plates in Inventor, a solid modeling program and cut them on the laser engraver at school. I was a bit apprehensive about the ability of the laser to cut the material I bough from Stew_Mac, but it cut beautifully. I pressed the magnets in then gave the assembly a coat of fast drying Polyurethane before attempting winding the wire.

My home-made winder was not counting correctly, so I decided to wing it and wind without counting. I got it to about the physical size of the pickup I had that had 5.5K ohms and stopped. I soldered on some leads and used a set of rare earth magnets I had to magnetize the Alnico pickup magnets. I guessed pretty well. It measured out at 5.89K Ohms. I still intend to pot the pickup in wax and wrap it with some black pickup tape, but I was too anxious to see if it worked, so I soldered together the volume and tone pots, wired up the jack, and plugged it in to the Amp. Success!

Here are some pictures of the instrument so far. Many, many things still left to do including redesigning the winder. FYI, after I got done winding the first pickup, I had a brain storm (fart) about how to get the winder to count and wind correctly, and it seems to work now. Now I just have to figure out counts and resistance.

http://smg.photobucket.com/albums/08...ic%20Mandolin/

Matt

[Terry Allan Hall]

I made my first pickup this week. I designed the top and bottom plates in Inventor, a solid modeling program and cut them on the laser engraver at school. I was a bit apprehensive about the ability of the laser to cut the material I bough from Stew_Mac, but it cut beautifully. I pressed the magnets in then gave the assembly a coat of fast drying Polyurethane before attempting winding the wire.

My home-made winder was not counting correctly, so I decided to wing it and wind without counting. I got it to about the physical size of the pickup I had that had 5.5K ohms and stopped. I soldered on some leads and used a set of rare earth magnets I had to magnetize the Alnico pickup magnets. I guessed pretty well. It measured out at 5.89K Ohms. I still intend to pot the pickup in wax and wrap it with some black pickup tape, but I was too anxious to see if it worked, so I soldered together the volume and tone pots, wired up the jack, and plugged it in to the Amp. Success!

Here are some pictures of the instrument so far. Many, many things still left to do including redesigning the winder. FYI, after I got done winding the first pickup, I had a brain storm (fart) about how to get the winder to count and wind correctly, and it seems to work now. Now I just have to figure out counts and resistance.

http://smg.photobucket.com/albums/08...ic%20Mandolin/

Matt

That one looks pretty good, actually!

[Chinn]

Top notch job. They look great!

[slausonm]

Thanks Terry and Chinn,

I'm pretty pleased with how the design is looking. Thanks to the feedback from all of you, I have decided to change a few things for next year's model which should make V2 better.

We still need to design and make a bridge. The bridge on the acoustic mando's we made were solid/non-adjustable, which was problematic for us newbies who don't setup mandolins on a regular basis. We got the strings almost perfect then we would go a bit too far and have to start over. So this years model will have an adjustable bridge. It will give me the opportunity to teach the kids how to make the knurled nuts and screws in the metal lathe. We also have to make the knobs for the volume and trim pots.Planning to make an injection mold for this. One of the kids has already designed a knob. More fun

Matt

[thistle3585]

Matt,
I'll give you a tip. The outside string spacing at the bridge shouldn't exceed the width of the neck at the 12th fret otherwise you risk the strings falling off the board around the 22nd fret. I have have some drawings of some tun o matics that I have made if you want them for reference. I've made them out of brass, ebony and rosewood. The class is very impressive.

Andrew

[slausonm]

Thanks Andrew,
I would love the info on your bridge. The administration leaves me alone most of the time to do some cool things with the students. They are very supportive. The group of kids I have are doing a good job and they learn quite a bit along the way.

Matt

[thistle3585]

Matt,
I thought I'd post this here so that anyone that wants the dimension can have them. Let me know if you have questions. This is how they are run on the CNC. The first set is ebony five strings followed by rosewood four strings and the brass versions in the back. The brass ones are run on a mill.

I did have some difficulties with the wood ones by the saddles tilting on me, but I think I have resolved that by putting a thin piece of binding in the bottom of the slot for the saddle to rest on.

Before everyone starts emailing me, "NO, I am not selling them but I will talk with Tom Morici at moongazermusic.com to see if he wants to carry them." With all the parts and such needed on these they cost about $200 and that doesn't include the tailpiece.

[slausonm]

Thanks for the images, Very nice!

The kids got a lesson in how expensive it is to make things. I had the kids price out the mandolins and "pay" themselves what they wanted to work for an hour. Materials, wages, rent, tooling rental... The average class cost of making the school Mandolins was about $750.
Matt

[thistle3585]

Not a problem, I hope they will be of benefit. Great idea on figuring their costs. Now you need to have them figure it out if they made 2, 6 or 12 unit batches. I think that would really give them an idea on building on a production basis. Next thing you know they'll start deciding which area of production should get paid more for their skill set.

[slausonm]

Not a problem, I hope they will be of benefit. Great idea on figuring their costs. Now you need to have them figure it out if they made 2, 6 or 12 unit batches. I think that would really give them an idea on building on a production basis. Next thing you know they'll start deciding which area of production should get paid more for their skill set.

Your pictures gave me some good ideas on designing the bridge.

We costed the mando's for a batch of 20. Divided $1000 monthly rent into hours, $1000 monthly tool rental and had them estimate work time as well as look up the cost of all of the materials. Not exactly realistic with ALL the costs involved in manufacturing, but it starts to hit home when they see it isn't free. We did discuss the fact that the design engineers were not going to get paid the same as the guys sweeping the floors or the skilled craftsman. Some of their sources were pretty funny... lumber liquidators apparently makes instrument veneer along with selling retail flooring

[slausonm]

I updated the e-mandolin video. Still not done, but closer.

http://www.youtube.com/watch?v=4LfKW...ature=youtu.be

Matt