really long magnetic pickup

Thread Starter

Bigjohn1955

Joined Dec 19, 2020
5
Hi folks! I am a newby around here and I have doubts about a design I am working on. I want to build a solid body lap harp with 20 steel strings and use a magnetic pickup to feed a standard guitar amp. The key is to have a single pickup unit with an impedance of roughly 2K. I could use 3 standard pickups through a simple op amp mixer, but that requires batteries, circuits, and a place to put them. Hand winding a coil on a ten inch bobbin is out of the question. A single loop transformer pickup has proven... Problematic. So now I am thinking about winding 20 small round bobbin coils, one for each string, and connecting them in series. Each coil at roughly 2K. They would all have a mutual magnetic field, and be connected in inductance aiding. Thoughts anyone?
 

Thread Starter

Bigjohn1955

Joined Dec 19, 2020
5
Oops sorry! The above single coils would be wound at 100 ohms each. By the time I figured out how to edit, the window had closed. Newbys! Whataya gonna do? Hehe!
 

Thread Starter

Bigjohn1955

Joined Dec 19, 2020
5
Have you looked over at this forum? https://music-electronics-forum.com/search?q=pickup+design&searchJSON={"keywords":"pickup+design"} Seems like many there have been doing some work on different pickups.
I have searched that that and several other forums. The folks on the pickup forums are pretty much in pursuit of the perfect six string pickup, which is understandable. I am just looking for basic function in a twenty string pickup, a device nobody but the piano people even seems to consider. How they do it is beyond me. They are not saying how they do it, (also understandable) and I can't afford to buy one. So I came here to get back to basics. Inductance, impedance, and a change in magnetic fields equals ... Maybe??

There is no purpose in the universe, there are only properties. Purpose is up to us.
 

Wolframore

Joined Jan 21, 2019
2,183
For pianos a transducer on the sound board and an actual microphone for capturing the reverberations in air is generally how it’s done, I’m sure it’s possible to put a pickup under the strings but I’m sure something like that would dampen the sound board.
 

Ian0

Joined Aug 7, 2020
1,120
The resistance of a guitar pickup may be around 2k, but the inductance is about 2H.
That means the impedance at 10kHz is more like 120k - which is why guitar amp inputs have a 1M input impedance; which is also why they have horrible problems with hum pickup and resonances which depend on lead capacitance and vary with lead length.

Do it properly (like the guitarists would have done if they were not such Luddites) - put a preamp on board and phantom power it!
 

shortbus

Joined Sep 30, 2009
8,171
I have searched that that and several other forums.
Just thought they might have some ideas.

I don't quite understand why the thought of winding a long coil would be so bad. Kind of like the *lipstick* pickups Danelectro used back in the 50's and 60's. You would need to make a bobbin though. A one off could even be wound by hand. Finding a single magnet for it might be hard though.

I'd love to see a drawing or picture of the harp. I love the sound of lap guitars, can't play a lick but love to hear both electric and especially Weissenborns. With only 20 strings will they be plucked like a normal harp or will they be fretted with a slide?
 

Ian0

Joined Aug 7, 2020
1,120
You could - some guitars have two pickups, and generally have a selector switch which can select either or both.
However, don't forget that you have trebled the inductance! A phantom powered preamp in the instrument would be REALLY good idea. If microphone manufacturers can find a space for the preamp, then I'm sure you can!
 

Thread Starter

Bigjohn1955

Joined Dec 19, 2020
5
Just thought they might have some ideas.

I don't quite understand why the thought of winding a long coil would be so bad. Kind of like the *lipstick* pickups Danelectro used back in the 50's and 60's. You would need to make a bobbin though. A one off could even be wound by hand. Finding a single magnet for it might be hard though.

I'd love to see a drawing or picture of the harp. I love the sound of lap guitars, can't play a lick but love to hear both electric and especially Weissenborns. With only 20 strings will they be plucked like a normal harp or will they be fretted with a slide?
They are strictly harp strings. No frets. You could attach harp levers to get a full scale, but they are pretty much a basic instrument. I have made several acoustic ones. I'll see if I can dig up a picture of one. The beauty of them is they were actually designed for people who "can't play a lick". The sheet music slips under the strings, and you follow a dotted line that shows exactly which strings to pluck in order. All you have to have is a basic idea of the beat and timing in your head. I had the notion that a solid body version would take the concept out of the middle ages. Google 'hog-nose psaltery' (I didn't name it). Anybody that ever did paint by number can play one.

About that one-off. I know it could be done... very slowly, but we are talking about about 4000 turns. A5 magnet slugs would give me all the field I would need. Maybe I am just being lazy and overthinking it.
 

shortbus

Joined Sep 30, 2009
8,171
They are strictly harp strings. No frets
Oh now I get what your making. Like Bertus said I know them as a Zither.

Have you looked at pickups used on pedal steel guitars? Pedal steels have more strings than a regular guitar, any where from 8 to 12 if I remember correctly, with 10 being very popular. just one of many makers - https://www.lollarguitars.com/lollar-steel-guitar-pickups/stringmaster But that said, will a wound electric pickup sound good or acceptable to most people? Have you thought of using piezo under saddle pickups? Again just one of many - https://hazeguitars.com/blog/piezo-pickups-evolve
 
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