DE102010056473B4 - Capacitive pickup system - Google Patents

Abstract

Capacitive pickup system (1) for a harmonica (2), which on one side of blow or drawing tuning plates (4a, 4b) of the body (3) clamped, a blowing or drawing current exposed Blasstimmzungen (5) and Ziehstimmzungen (6) metallic material which, connected to a pole of a voltage source, form capacitive electrodes whose respective distances to a capacitive counterelectrode are variable during tone generation and which serve to generate an electrical signal indicative of a change in capacitance between the respective oscillating electrodes and is based on the opposite electrode, characterized in that the capacitive counter electrode (8, 9) in each case for the Blasstimmzungen (5) and for the Tiehstimmzungen (6) is strip-shaped and arranged so that, viewed over the length of the strip-shaped counter electrode, the dielectric between the Electrodes and the counter electrode the greatest possible distance from blow or Z iehstrom takes and the counter electrodes (8, 9) for this purpose immediately at the beginning of the free swing zone behind the clamping points (10) of the blowing or drawing tongues sits.

Description

The present invention relates to a capacitive pickup system for a harmonica.

A harmonica has a so-called body on which the blowing or Ziehstimmzungen are attached to so-called blowing or Ziehstimmplatten.

The blowing or Tiehstimmzungen are for this purpose riveted on one side at the ends of the so-called voice holes and, since the voice holes is slightly larger than the floor plan of the blowing or Ziehstimmzungen freely swing into the tuning holes.

Since the blowing or Ziehstimmzungen consist of metallic material, one makes use of the so-called capacitive conversion in which a change in the electrical capacitance during the oscillation process, an electrical signal is generated, which then via a corresponding amplifier for output on a Speaker is processed.

The blowing or Tiehstimmzungen therefore form capacitive electrodes which are connected to the negative pole of a DC voltage source while a corresponding capacitive counter electrode spans the Blas- or Ziehstimmzungen and is connected via a series resistor to the positive pole of the DC voltage source.

As a result of the change in distance between the blowing or pulling tabs and the capacitive counter electrode, the capacitance of the capacitor formed thereby changes. If the capacitance increases, the charge flows, the capacitance decreases, the charge flows off. This charge movement is an alternating electrical current that flows through an ohmic resistor and produces an alternating voltage at this, which represents the desired output signal.

From the US 3322875 A Such a capacitive pickup system for a harmonica is known in which in each case a capacitor plate insulated on both sides is positioned as a counterelectrode between the cover plates and the metal plates equipped with blowing or pulling tongues and extends over the entire comb surface.

The US 6326532 B1 describes a generic pickup system for a harmonica, consisting of a board, which is equipped with sensor components that convert the mechanical vibrations of the blowing and Ziehstimmzungen into electrical signals. The number of sensors corresponds to the number of blowing or Ziehstimmzungen. The sensors may alternatively be sensors of inductive, capacitive or optical type or so-called cup-core or Hall effect sensors

Subject of the US 2901936 A is a transducer for converting mechanical to electrical vibrational energy in which the reeds and the reed carrier, representing the vibrating electrode and the counter electrode respectively, form a capacitor system.

It is now necessary to design the electrostatic sound pickup on the reeds in such a way that negative disturbances are avoided as far as possible.

These negative interferences are caused for the most part by the influence of moisture-laden breathing air.

It must therefore be ensured that the droplet flight through the dielectric, which is located between the capacitor electrodes, is reduced as much as possible.

This object is achieved by the invention with the features of the main claim.

From the invention, there is the advantage that a capacitance change between the electrodes, which are formed by the reeds and the counter electrode due to a change in the dielectric conductivity of the dielectric by droplet loading is practically excluded, so that the capacitance change solely due to the change in geometric relationships between the electrodes and the counter electrode are decisive for the tone generation.

This advantage is achieved in that the counter-electrodes, which are practically stationarily connected to the blowing or drawing current plates, are arranged virtually completely outside the blowing or drawing current.

For this purpose, the capacitive counter-electrodes are always directly at the beginning of the free oscillation zone d. h., Located immediately adjacent to the Einspannstellen the reeds.

There is indeed due to the swing image, which form the reeds, the geometric change of the distance between the electrodes and the counter electrode only very small, so that only a relatively small output signal is produced, which can not be impressed so a power amplifier.

On the other hand, however, any interference by moisture-laden air is effectively counteracted.

It is essential to the extent that the counterelectrode is in each case directly adjacent to the fixed end of the reeds and also has only a very small extent in the longitudinal direction of the reeds, so that it does not get into the region of the moisture-laden air stream.

Expediently, the counterelectrode for the blow tongues furthermore protrudes comb-shaped into the punched-out vocal hole of the respective blow tongues in order to sit as close as possible to the blow tongues tongue. Since the Blasstimmzungen are fixed on the opposite side of the counter electrode to the Blasstimmplatte, the comb-shaped electrode shape serves the purpose that the prongs protrude into the recess of the Stimmlochstanzung.

Since the Ziehstimmzungen are mounted on the side facing the counter electrode of the Ziehstimmplatte, here the distance can be chosen arbitrarily small without special shaping. Conveniently, the distance to the reeds is chosen as small as possible in both counter electrodes, without restricting the movement of the reeds. Thus, the space effective as a dielectric is minimized and thereby captured only insignificantly by the moisture-laden flow.

Conveniently, the counter electrodes are strip-shaped and extend over the entire reeds of the blowing or drawing stream side.

It is recommended that the respective counterelectrodes be attached to the corresponding voice plates at the side of the blow or pull tabs.

In particular, in the Blasstimmzungen beyond the capacitive counter electrode should be formed like a comb and protrude with their teeth in the punch holes of the Blastimmplatte.

Since the output signals generated in this way are relatively small, they must be processed via a preamplifier in order to ultimately become an audio-capable signal via an amplifier.

It is therefore also proposed to attach a preamplifier directly to the harmonica.

In fact, for this case, only short electrical lines are required to bring the capacitive signals to the preamplifier. This counteracts the influence of electromagnetic interference fields.

Furthermore, the preamplifier should sit in a metallic housing to shield electromagnetic interference fields.

In this case, the preamplifier may be mounted on the opposite side of the playing side of the harmonica, so that it forms together with the housing of the harmonica a compact unit whose appearance does not differ practically from the appearance of a harmonica.

Furthermore, it should be noted that for certain types of tone generation, referred to as bends, both the bleach tabs and the die tabs vibrate simultaneously. In this case, inevitably arise two signals in a phase offset by 180 degrees, which must be processed by the preamplifier ultimately.

For this purpose, it is proposed to construct the preamplifier as a differential amplifier with two inputs.

For this purpose, the first input of the amplifier has a first amplifying stage and a second inverting stage. This input is to be connected to the counter electrode of the Blasstimmzungen whose signal is thereby amplified and rotated by 180 degrees. The second input has only one amplifying step and is connected to the counter electrode of the pull tuning tabs. The signal of the Ziehstimmzungen is thereby only amplified. In the mixing stage, the two signals are combined additively. Thus, the different phase position of the signals is corrected and the sum signal at the output of the mixer can be supplied to a power amplifier.

Furthermore, it is recommended to equip the preamplifier with low-noise field effect transistors, so that even at a low signal level only the smallest possible currents are required to eliminate the amplifier noise as much as possible.

Furthermore, it is recommended to arrange the capacitive counter-electrodes of both the Blasstimmzungen and the Tiehstimmzungen each directly under the covers of the harmonica on the corresponding reeds.

Will you continue the basic idea of the invention, namely the avoidance of moisture-laden air by that of the capacitive To avoid sending units formed dielectric, it is also recommended to provide the cover of the harmonica on the one hand on its large surface with perforation holes, so that the air can escape unhindered there and on the other hand to connect the cover of the harmonica with the ground potential of the preamplifier.

Thus, the capacitive counterelectrodes are shielded and since the ventilation openings and the perforation holes can remain small, the shielding effect is unimpaired.

Furthermore, both counterelectrodes and their connection lines to the preamplifier inputs are completely provided with an insulating coating, so that no leakage currents can occur due to the precipitating moisture.

The power sources necessary for the operation of the preamplifier and the capacitive transducer are then housed in an external housing according to the invention, which can be worn on the belt, for example. This battery case has an input jack that connects to the preamplifier with a suitable three-pin cable. This connection transmits as it were the supply voltage of the preamplifier and the Nutzsignalwechselspannung from the preamplifier output in the battery case. The battery housing also has a volume control and an output jack for the useful signal. About the output jack, the useful signal can be supplied to a power amplifier.

In the following the invention will be explained in more detail by means of exemplary embodiments.

Show it:

1 an embodiment of the invention without a lid overlooking the Blasstimmzungen

2 a view on a harmonica on the game page

3 a view of a harmonica on the side of the drawing voice plate

4 an axial view

5 a harmonica with a raised lid

6a -C is a view showing the arrangement of the counter electrodes and the course of the blowing current or drawing current and bending

7 schematic circuit diagram for a preamplifier

8th Schematic representation of the electrical signal generation up to the output of the preamplifier

Unless otherwise stated below, the following description applies to all figures.

The figures show a capacitive pickup system 1 for a harmonica 2 ,

Such a harmonica has a body 3 on, consisting of two mutually parallel voice plates 4a . 4b exists between them the body of the pulpit 2 ' lock in.

In the embodiments shown, the voice plate is 4a as Blasstimmplatte and the voice plate 4b designed as a drawing voice plate.

Accordingly sit on the Blasstimmplatte the Blasstimmzungen 5 or on the drawing voice plate the Ziehstimmzungen 6 , The blow or pull tabs are slightly smaller in plan than the respective punch holes 7 , which allow the respective reeds a free swing around the zero position.

As a result of the prevailing currents within the corpus, this so-called zero position is shifted when playing the harmonica. The closer you are to the end of the swinging tongue, the weaker this shift is. Accordingly, the localization of the counterelectrodes near the fixed end of the reeds and the small expansion of the counterelectrode in the direction of the reeds render the influence of the shift of the zero position on the signal negligible.

This arrangement of counterelectrodes also avoids the unwanted expander effect and obtains the desired undistorted signal tap.

The Blasstimmzungen or Ziehstimmzungen are riveted from metallic material and each end of their voice plates.

If the harmonica is played, the air column in the throat and trachea area gets into vibration. This air column vibration is stimulated by the movement of the reed, which determines the pitch (mood). Experienced musicians, however, can change the pitch by changing the pharynx and diaphragm, which is called bending or over-bending.

It is now necessary to convert all these sounds into electrical signals in order to be able to output them realistically and as far as possible without any background noise via an amplifier and a downstream loudspeaker.

For this purpose, a counterelectrode is assigned to the respective electrodes, which form the blowing or pulling tuning tongues, so that a capacitive structure arises whose capacitance changes with the oscillating motion of the respective reeds.

The resulting changing electrical signal is then applied to a corresponding preamplifier.

For this purpose, according to the invention, both the capacitive counter electrode 8th for the blow tabs 5 as well as the capacitive counter electrode 9 for the pull tabs 6 each formed strip-shaped and arranged so that considered over the length of the strip-shaped counter electrodes, that the dielectric between the electrodes, which are formed by the reeds and the respective counter electrodes, the greatest possible distance from the blow stream or drawing current and for this purpose immediately at the beginning of the free Oscillating zone sits behind the clamping points of the blowing or drawing tongues.

The clamping of the respective blowing or Ziehstimmzungen is determined by the common support and contact surface between the clamped end of the reed and the respective voice plate.

With her the clamping point 10 outstanding length portion can therefore swing the respective reed freely in the associated tuning hole and the vibration can be tapped according to the invention capacitively.

Therefore, the respective counter electrode sits almost immediately at the beginning of each oscillation zone behind the clamping point of the reed with the following proviso:
The pulling tongues 6 sit outside on their drawing voice plates 4b immediately below the respective lid 18 ,

The corresponding counter electrode 9 therefore spans with its consistently smooth bottom 11 all pull tabs at the same distance.

The blow tongues 5 sit on her whiteboard 4a and are installed from the inside.

Therefore, when exposed to a blast stream, they can swing freely toward the lid.

In the case of Bendings and Overbendings ( 8c ) the reeds are exposed to both a blowing stream and a drawing stream.

In order to be able to tap the relatively small capacitive signal effectively, therefore, the counter electrode of Blasstimmzungen, as in particular 6 shows, equipped with a comb-like underside, with their projecting tines in the punched holes 7 the Blasstimmplatte protrudes to sit as close to the Blasstimmzungen.

In particular 6 and 8th On the one hand, it can be completely avoided in this way on the one hand that the blowing stream or drawing stream passes through the dielectric between the electrodes and the counterelectrodes and, on the other hand, that a relatively small distance between electrodes and counterelectrodes can be realized despite the thickness of the respective voice plates.

Furthermore, the figures show that the preamplifier 13 can be attached directly to the harmonica.

The preamp 13 sits the game page 14 opposite to the mouth of the harmonica in a tubular metallic body 15 ,

The metallic tubular body primarily serves the purpose of shielding electromagnetic fields.

Since an electrical alternating voltage signal results from the capacitors formed in each case by electrodes and counterelectrodes, this can be used to generate the signal required for the loudspeaker.

But this is only possible with the electronic preamplifier.

The required useful signal is in the form of a very small AC voltage to the capacitor plates and is picked up there to control the preamplifier.

As a result, the capacitor, which is formed by the electrodes and counter electrodes, charge withdrawn. It comes to an AC flow from the capacitor plates to the preamplifier. This power output reduces the AC voltage across the capacitor.

To that extent the voltage applied to the capacitor electrodes AC voltage is not unnecessary fall off, the preamplifier must have a high input impedance.

The high input resistance in turn ensures a low alternating current flow, whereby in addition the noise of the amplifier remains low due to the use of low-noise field-effect transistors.

As for this 7 and 8th show, the amplifier has two inputs.

The first input goes to a first amplifying stage Q1 and a downstream second inverting stage Qi.

The second input goes to a boosting stage Q2. The output of Q2 and the output of Qi are merged in the adding mixer QM. If, as in the case of Bendigs, signals appear at both inputs, they inevitably have opposite phase angles. In this case, the inverting stage Qi causes the phase position to be equalized before the signals in the mixer stage QM are added.

At the output of the mixer QM thus a sufficiently large output signal is provided, which is supplied to a downstream power amplifier for the generation of a speaker suitable signal.

Furthermore, it is shown that the preamplifier has two end connection sockets 16 which can alternatively be used.

One of the two sockets is connected to the input socket of the battery case via a suitable cable to bring the supply voltage to the preamplifier and to transfer the useful signal from the preamplifier output to the battery case. In the battery case, the useful signal is routed via a volume control to an output jack, which can be connected to a power amplifier.

Furthermore, it shows in particular 5 that the lids 18 the harmonica are provided with perforation holes, which are mounted in rows on the large surface of each cover next to each other.

In this way, the air flow emerging from the vents can escape directly through the perforation holes to the outside without affecting the dielectric between the electrodes formed by the reeds and the associated counter electrode.

The hole diameters are therefore chosen so small that the shielding effect of the metallic cover is retained with respect to the capacitor function of electrodes and counterelectrodes.

In addition, it is advisable to set the metallic lid on the same potential as the metallic tubular body of the preamplifier, in order to use here also the additional shielding effect.

Furthermore, in the 6a to 6c the insulating layer 20 around the counter electrodes 8th and 9 recognize the blowing and Tiehstimmzungen. The insulating coating completely encloses the counter electrodes and their leads to the preamplifier inputs. This creepage currents are prevented by the precipitating moisture.

Furthermore, the show 6a to 6c the localization of the counterelectrodes close to the fixed end of the reeds and their small extension in the longitudinal direction of the reed.

This will be discussed in more detail below.

At the blow control panel 4a the bleach tongues are sitting 5 and are inside the pulpit body 2 ' arranged. At the drawing voice plate 4b the pulling tongues are sitting 6 and are outside the pulpit body 2 ' arranged.

It is an observed effect that the invention makes use of.

How the particular 6a to 6c show, the blow tongues bend 5 at a blow stream into the body of the pulpit 2 ' into it, while the Ziehstimmzungen 6 with a pulling air flow to the outside of the drawing voice plate 4b bend away.

This effect causes the blowing or drawing current can also flow around the Blasstimmzungen or Ziehstimmzungen laterally into the punch holes of the reedplates.

It therefore creates a gusset, the clamping point 10 starting increasingly towards the free end of the respective reeds and allows the passage of the respective air flow.

Since the air flow naturally goes the path of least resistance, the major part of the air flow will take the path through the largest possible free cross section between the reeds and the reeds and at most only a very small portion of the air flow is at the very narrow cross sections of the gusset, the towards the chuck end 10 occur, passed.

However, this means taking into account the technical deflection of the reeds 5 respectively. 6 in the area of the counterelectrodes 8th respectively. 9 There are virtually no free cross-sections available, so that it does not have to be expected that significant portions of the moisture-laden air stream pass through.

The opposite is the case.

Due to the increasing flow resistance towards the closed end of the gusset between the reeds and the respective voice plates can be achieved that with the arrangement of the counter electrodes 8th respectively. 9 in the first third or first quarter or first fifth of the total length of the reeds, from the clamping point 10 From considered, moisture-laden air is not passed through the dielectric of the respective capacitor array, so that noise effects are reliably avoided.

The arrangement of the counter electrodes 8th respectively. 9 can be determined by experiment, if necessary, whereby the limit position would be determined by just barely perceptible to human hearing noise due to moisture-laden air.

However, this limit position can also be closer to the clamping point 10 can be introduced without departing from the basic idea of the invention, because the noise occurring can also be determined electronically, even if it is no longer perceptible by the human ear.

LIST OF REFERENCE NUMBERS

1

Capacitive pickup system

2

harmonica

2 '

Comb

3

corpus

4a

Voice plate, blasseite

4b

Voice plate, pull side

5

Pale tongue Timm

6

Timm pulling tongue

7

punch hole

8th

Capacitive counter electrode, blowing current

9

Capacitive counter electrode, pulling current

10

clamping

11

bottom

12

Comb-like prongs

13

preamplifier

14

game page

15

Metallic pipe

16

Connection socket, amplifier, alternative

17

Connection socket, amplifier

18

cover

19

perforation

20

Insulating coating

Claims (13)

Capacitive pickup system ( 1 ) for a harmonica ( 2 ), which on one side of blowing or Ziehstimmplatten ( 4a . 4b ) of the body ( 3 ), a blowing or pulling stream exposed, Blasstimmzungen ( 5 ) and pull tabs ( 6 ) made of metallic material, which, connected to a pole of a voltage source, form capacitive electrodes whose respective distances to a capacitive counterelectrode are variable during tone generation and which serve to generate an electrical signal resulting from a change in capacitance between the respective oscillating ones Electrodes and the counter electrode, characterized in that the capacitive counter electrode ( 8th . 9 ) in each case for the blow tabs ( 5 ) and for the pull tabs ( 6 ) and is arranged such that, considered over the length of the strip-shaped counter electrode, the dielectric between the electrodes and the counter electrode occupies the greatest possible distance from blowing or drawing current and the counterelectrodes ( 8th . 9 ) for this purpose immediately at the beginning of the free swing zone behind the clamping points ( 10 ) of the blowing or drawing tongues is seated. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to claim 1, characterized in that the capacitive counter electrode ( 8th . 9 ) on the blowing or drawing voice plate ( 4a . 4b ) of the harmonica ( 2 ) is attached laterally next to the blowing or the drawing tongues. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to claim 1 or 2, characterized in that the capacitive counter electrode of Blasstimmzungen is comb-like and with your teeth in the punched holes of Blasstimmplatte ( 4a ). Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to one of claims 1 to 3, characterized in that the electrical signal from electrodes and counterelectrodes is led via electrical lines to a preamplifier which is connected directly to the harmonica ( 2 ) sits. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to claim 4, characterized in that the preamplifier ( 13 ) in a metallic tube ( 15 ), which is opposite the game side between the air outlet or air inlet openings on the body ( 3 ) is attached. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to claim 4 or 5, characterized in that the preamplifier ( 13 ) has two inputs, wherein the input signal of the first input of an amplifier stage and a subsequent, inverting stage is supplied, the input signal of the second input of an amplifier stage is supplied, and is subsequently added in a mixing stage with the output signal of the inverting stage of the first channel. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to claim 6, characterized in that the output of the mixing stage is connectable to an amplifier. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to one of claims 4 to 7, characterized in that the preamplifier ( 13 ) is equipped with low-noise field effect transistors. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to one of claims 1 to 8, characterized in that the capacitive counterelectrodes of both the blowing tongues and the drawing tongues respectively directly under the covers ( 18 ) of the harmonica ( 2 ) on the blowing or drawing voice plate ( 4a . 4b ) to sit. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to claim 9, characterized in that the capacitive counterelectrodes of lids ( 18 ), which in their large area have perforation holes ( 19 ) are provided. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to one of claims 4 to 10, characterized in that the covers ( 18 ) of the harmonica ( 2 ) electrically conductive with the ground potential of the preamplifier ( 13 ) are connected. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to any one of claims 4 to 11, characterized in that the voltage source and regulator external to the harmonica ( 2 ) and with the preamplifier ( 13 ) can be connected by means of connection sockets and connecting cables. Capacitive pickup system ( 1 ) for a harmonica ( 2 ) according to one of claims 4 to 11, characterized in that the counterelectrodes and their connection lines to the preamplifier inputs are completely covered with an insulating coating ( 20 ) are provided.

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