About pickups (advice homemade). Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Musician

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It's much easier to get a good guitar now than say 40 years ago. But still, perhaps due to the financial side of the issue, I think there are still DIY enthusiasts who make guitars with their own hands. Here it is for them, beginners, and my note of an amateur musician is addressed.

Our first attempts to electrify an ordinary acoustic guitar were made with a friend, Sergey Omelchenko, back in 1966.

The simplest solution was to attach a piezoelectric transducer head from a turntable to the body of the guitar. Later, the piezoelectric element itself was taken out and a special holder was made for it, combined with a socket for connecting a shielded connection cable to the amplifier. This wooden structure was glued to the body of the guitar near the tailpiece. To increase the signal level, a plasticine ball was placed at the end of the piezoelectric sensor plate to increase the moment of inertia of the transducer. The signal was sufficient to connect to any radio receiver with a high-impedance record player input. This first "pickup" is depicted in Fig.0. Its disadvantage was its high sensitivity to acoustic noise, rustling, whistling of fingers along the strings and the mechanical fragility of the piezoelectric plate itself. But the cost of the pickup head assembly was only 1r.60 kopecks, and you can make a holder in half an hour with a simple tool.

The next homemade was a "real" electromagnetic pickup from the headphones of flight headsets. Headphones (telephone capsules) with a resistance of 2200 ohms were used, which are practically not found today. Carefully splitting the case, they removed the magnetic system of the phones as an assembly with two coils on the pole pieces of the magnets. These pole pieces matched the string spacing of the guitar in an amazing way.

Having split three earpieces (unfortunately, sometimes more were needed), magnetic cores were glued on a brass plate and all the coils were connected in series. A pickup with a resistance of 6600 Ohm was obtained, giving a fairly powerful electrical signal (Fig. 1). Instead of glue, it would still be better to use the soldering of pole pieces to a brass plate to fix the magnetic circuits, and cover it with a shielding and protective screen at the same time. But our meaningful struggle with electrical and magnetic interference began a little later ... A lot of such pickups were made (just imagine how many headsets were damaged :-)) and they were no longer equipped with acoustic, but home-made plywood "electric guitars". But the sound of these pickups was "doll". Due to the non-uniformity of the magnetic field near the pole pieces, the vibrations of the strings were converted into an electrical signal non-linearly, "enriching" the sound with harmonics and causing a feeling of "garbage" in the signal.

In the next pickup (in Fig. 2), this drawback has already been eliminated. Coils were placed on individual magnets for each string, each containing 4000 turns of PEL wire 0,08 mm in diameter, connected in series. It turned out to be a combination of 6-7 string pickups in one design, placed in one common plastic mass box. Painting the inside of the box with silver to shield the pickup showed the complete failure of such a solution.

The sound was clear, proportional to the vibrations of the strings, but not strong enough. I believe that the pickup lacked a magnetically soft steel plate instead of a plastic base, in addition, many small magnets created a slight local field for the strings. Well, purely speculative, imagine how difficult it was for the signal of individual strings to "penetrate" through the inductance of the remaining 5-6 coils!

The pickup turned out to be much better (Fig. 3) containing only one, but a powerful magnet, and one large coil. Its magnetic circuit - the base concentrated a powerful and uniform magnetic field near the strings, also well protecting the coil from damage. Topped with a brass screen, the pickup was insensitive to electrostatic interference and gave a strong, clear sound. Its only significant drawback, however, characteristic of most electromagnetic pickups, was its sensitivity to an external alternating magnetic field created by various transformers and network wires.

Well, the pickup in Fig. 4 has the best characteristics, which differs from the previous design only in the presence of identical dual coils. Absolutely the same, wound at the same time and put on a common magnetic circuit, they generate the same signal under the influence of an external magnetic field. But being included in the opposite direction, they mutually destroy the same interfering signal, providing the pickup with insensitivity to external magnetic interference. This turned out to be especially important when using various boosters, limiting amplifiers and fuzz devices.

By adding a guitar with a polarity switch for one of the coils (Fig. 6), you can get a significantly different sound when turned on in-phase and anti-phase. The suppression of magnetic interference occurs only when the coils are turned on in antiphase. In general, such a counter connection of coils on a common magnetic system forms an interesting spatial-frequency filtering of the signal of vibrating strings!

And finally, general recommendations for homemade pickups:

- all metal parts of the pickups must be interconnected and grounded, preferably by soldering;
- absolutely all the details of the pickups must be rigidly fixed, and not allow "bounce" to eliminate clicks, overtones and microphone effect;
- for a strong signal, it is desirable to make coils with the maximum possible number of turns, filling all available space with the winding and using wires with a diameter of 0,06-0,08 mm or even thinner - be sure to use an electrostatic screen for coils and connecting wires, however, to combat vortex currents and losses associated with them, this screen must have transparent windows opposite the strings (Fig. 5)

- do not use adjusting screws as part of the poles of the magnetic circuit to equalize the sound strength of the strings, it is better to use magnetically aligned ferromagnetic strings. The parasitic mic effect, hooks and string breaks caused by these screws will convince you of the viciousness of such constructions;
- use maximum strength magnets (cobalt ferrites) for more signal and better signal-to-noise ratio;
- use only rigid and reliable mechanisms for adjusting the position of the pickups relative to the strings or do not use them at all, setting the pickup immediately optimally;
- disassemble and study "proprietary" pickups - there is nothing that DIYers could not do the same or even better!

The pickup, having a significant inductance and interturn capacitance, together with the capacitance of the connecting shielded cords and the resistance of the regulators and the load, has a complex frequency dependence. The maximum reduction in the capacitance of the cords, due to their length, and the increase in load resistance has a positive effect on the quality of the guitar signal. More here.

However, good luck!

Author: E. Shustikov (UO5OHX ex RO5OWG); Publication: shustikov.by.ru

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