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Non investing amplifier microphone stand

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Generally people connect them to unbalanced microphone inputs of power amplifiers. The resulting sound is more often than not, harsh and metallic. Here we propose a much better solution, based on a good understanding of the nature of piezoelectric transducers. A piezo disk basically is and behaves as a capacitor, generating a voltage when exposed to vibration.

As a consequence, the impedance is a function of excitation frequency and can be considered infinite when no signal is generated. Such a generator makes a very bad source for a regular microphone input with constant input impedance. Here is a much better solution: The opamp in this circuit is configured as a current amplifier. Basically the piezo disk connects to the inverting input and thus sees a zero impedance.

It is virtually shorted. Note that Av is inherently independent of frequency here, thus we avoid the sharp and metallic sound obtained when using a non-inverting opamp configuration. The 22 MOhm resistor limits DC gain and prevents oscillation. It determines the low frequency roll-off. The higher this resistor, the lower the cutoff frequency. Resistors with such high values - values up to MOhm can be used- are not common.

Note that when using very high resistor values here, the opamp used must be a type with very low drift. The 1N diode about any type will do serves as polarity reversal protection, no luxury as we noticed many users try connecting a battery in its holder until it fits It can be exchanged for any low noise low voltage type.

The PCB has the size of a 9V battery and thus can be mounted on a battery holder. A typical application of this circuit was for an amplifier for a contact microphone picking up the vibrations of a cello bow. For this project, a small piezo disk was clamped via a small wooden bridge between the bow hair and the wood of the bow. Here is a picture: A shielded highly flexible silicon wire should be used, as stiff wires will cause unwanted noises. A variation of this circuit was worked out to facilitate connection to standard mixing boards with provisions for phantom powered microphones.

The phantom voltage is 48V but only a few mA can be drawn, so we must take care to select a low power opamp in the circuit:. This is a transformerless design, but audio transformer designs are possible as well. Here is a circuit for a PCB accommodating 4 separate piezo disk inputs and four phantom powered transformer balanced outputs:. If other transformers are used, the foot print may need to be changed accordingly.

Here is a picture:. One serious problem often met when using piezo disks as pickups in live electronic projects is that very high voltages spikes can be produced on strong excitation of the disks. This can eventually lead to destruction of either the power amplifier or the speaker system driven by it.

Also, it's not too healthy to the ears of the audience Hence the need for some kind of limiting or even compression of the signals. The diode circuit following the first amplifier stage, makes a limiter. If the signal on the input exceeds the diode forward voltage drop ca. With the 1k series resistor and the 47nF capacitor as drawn, the -6 dB point is at 3. The response time is determined by the RC time for the 47 nF and 2.

It is the kind of circuit that once was very popular amongst short-wave radio amateurs for listening to Morse code broadcasts. The germanium diodes AA , OA91 etc. Do not use regular silicon diodes, as at clipping, they will cause the second op amp to saturate. This is because the peak voltage of the signal with regular silicon diodes equals 1. As the second op amp has a gain of 10, the output should become 12 Vpp, a value that could only be reached when the power supply is higher than 12 V.

If you find the operation of the soft limiter still sounding too harsh for your application, increase the value of the 47nF capacitors. If you want to increase the attenuation, increase the value of the 1k resistor connected to the output pin 6 of the first op-amp. The final opamp, just mixes and amplifies the signal further to a strong and hefty line level.

A typical application for such a circuit was in the construction of a pick up to be used to amplify human heart beats. For this project a quite large piezo disk should be used 30 mm diameter or so and a weight should be glued with silicon compound to the upperside of the disk. This kills unwanted higher frequency signals right at the source. Of course, components have to be selected for optimum very low frequency performance. The limiter circuit adequately protects against spikes here.

Similar applications are: larynx microphones and monitoring devices for all sorts of body sounds. For my own 'Woman's Quartet', I even made a set of four vagina microphones As in some applications such as sound sculptures and audio art, often the signals of more than a single piezodisk are to be combined, a mixer circuit comes in handy. Here is the corresponding circuit:. In the following and more elaborate project design, we combined these ideas to realize a 5 channel piezo disk mixer, with individual channel volume controls as well as a master volume control.

Here is the circuit:. Note that metal film resistors should be used throughout for lowest possible noise. The mixer stage can make use of an TLO AD datasheet or TLC datasheet opamp, but if the circuit is to drive long cables, the AD makes a better choice, as it can drive quite large capacitive loads without stability problems.

The headroom and maximum output voltage swing of this circuit can be improved by raising the power supply voltage. Make sure not to exceed the absolute maximum ratings for the opamps used. If different types of opamps are used in this circuit it is mandatory to go for JFET input low noise types, preferably with output swings up to the supply voltage.

Also, make sure to check the minimum Vcc voltage for the part. If specified at higher than 9V, consider using a 12V or higher voltage battery pack. The AD performs very well here, but it's a rather expensive component. In quite many experimental instrument building and soundsculpture applications, it is not required to build the circuit with input volume control potentiometers. If the circuit is to be build into such a project, the potmeters can be replaced by fixed resistors.

As a result, the region where both devices simultaneously are nearly off the "dead zone" is reduced. The result is that when the waveforms from the two devices are combined, the crossover is greatly minimised or eliminated altogether. The exact choice of quiescent current , the standing current through both devices when there is no signal, makes a large difference to the level of distortion and to the risk of thermal runaway, that may damage the devices ; often the bias voltage applied to set this quiescent current has to be adjusted with the temperature of the output transistors for example in the circuit at the beginning of the article the diodes would be mounted physically close to the output transistors, and chosen to have a matched temperature coefficient.

Another approach often used as well as thermally tracking bias voltages is to include small value resistors in series with the emitters. Class AB sacrifices some efficiency over class B in favor of linearity, thus is less efficient below It is typically much more efficient than class A. Sometimes a numeral is added for vacuum-tube stages.

If the grid voltage is always negative with respect to the cathode the class is AB 1. If the grid is allowed to go slightly positive hence drawing grid current, adding more distortion, but giving slightly higher output power on signal peaks the class is AB 2.

The usual application for class-C amplifiers is in RF transmitters operating at a single fixed carrier frequency, where the distortion is controlled by a tuned load on the amplifier. The input signal is used to switch the active device causing pulses of current to flow through a tuned circuit forming part of the load. The class-C amplifier has two modes of operation: tuned and untuned. This is called untuned operation, and the analysis of the waveforms shows the massive distortion that appears in the signal.

When the proper load e. The first is that the output's bias level is clamped with the average output voltage equal to the supply voltage. This is why tuned operation is sometimes called a clamper. This allows the waveform to be restored to its proper shape despite the amplifier having only a one-polarity supply. This is directly related to the second phenomenon: the waveform on the center frequency becomes less distorted.

The residual distortion is dependent upon the bandwidth of the tuned load, with the center frequency seeing very little distortion, but greater attenuation the farther from the tuned frequency that the signal gets. The tuned circuit resonates at one frequency, the fixed carrier frequency, and so the unwanted frequencies are suppressed, and the wanted full signal sine wave is extracted by the tuned load. The signal bandwidth of the amplifier is limited by the Q-factor of the tuned circuit but this is not a serious limitation.

Any residual harmonics can be removed using a further filter. In practical class-C amplifiers a tuned load is invariably used. In one common arrangement the resistor shown in the circuit above is replaced with a parallel-tuned circuit consisting of an inductor and capacitor in parallel, whose components are chosen to resonate the frequency of the input signal. Power can be coupled to a load by transformer action with a secondary coil wound on the inductor. The average voltage at the drain is then equal to the supply voltage, and the signal voltage appearing across the tuned circuit varies from near zero to near twice the supply voltage during the rf cycle.

The input circuit is biassed so that the active element e. The active element conducts only while the drain voltage is passing through its minimum. By this means, power dissipation in the active device is minimised, and efficiency increased. In the class-D amplifier the input signal is converted to a sequence of higher voltage output pulses.

The averaged-over-time power values of these pulses are directly proportional to the instantaneous amplitude of the input signal. The frequency of the output pulses is typically ten or more times the highest frequency in the input signal to be amplified. The output pulses contain inaccurate spectral components that is, the pulse frequency and its harmonics , which must be removed by a low-pass passive filter. The resulting filtered signal is then an amplified replica of the input.

These amplifiers use pulse width modulation, pulse density modulation sometimes referred to as pulse frequency modulation or a more advanced form of modulation such as Delta-sigma modulation for example, in the Analog Devices AD class-D audio power amplifier. Output stages such as those used in pulse generators are examples of class-D amplifiers.

The term class D is usually applied to devices intended to reproduce signals with a bandwidth well below the switching frequency. Class-D amplifiers can be controlled by either analog or digital circuits. The digital control introduces additional distortion called quantization error caused by its conversion of the input signal to a digital value. The main advantage of a class-D amplifier is power efficiency.

Because the output pulses have a fixed amplitude, the switching elements usually MOSFETs , but valves vacuum tubes and bipolar transistors were once used are switched either completely on or completely off, rather than operated in linear mode. A MOSFET operates with the lowest resistance when fully on and thus excluding when fully off has the lowest power dissipation when in that condition.

Compared to an equivalent class-AB device, a class-D amplifier's lower losses permit the use of a smaller heat sink for the MOSFETs while also reducing the amount of input power required, allowing for a lower-capacity power supply design.

Therefore, class-D amplifiers are typically smaller than an equivalent class-AB amplifier. Class-D amplifiers have been widely used to control motors , and are used almost exclusively for small DC motors, but they are now also used as audio power amplifiers, with some extra circuitry to allow analogue to be converted to a much higher frequency pulse width modulated signal. High quality class-D audio power amplifiers have now appeared on the market.

These designs have been said to rival traditional AB amplifiers in terms of quality. An early use of class-D amplifiers was high-power subwoofer amplifiers in cars. Because subwoofers are generally limited to a bandwidth of no higher than Hz, the switching speed for the amplifier does not have to be as high as for a full range amplifier, allowing simpler designs. Class-D amplifiers for driving subwoofers are relatively inexpensive in comparison to class-AB amplifiers.

The letter D used to designate this amplifier class is simply the next letter after C , and does not stand for digital. Class-D and class-E amplifiers are sometimes mistakenly described as "digital" because the output waveform superficially resembles a pulse-train of digital symbols, but a class-D amplifier merely converts an input waveform into a continuously pulse-width modulated square wave analog signal. A digital waveform would be pulse-code modulated. As said in the class-D amplifier, the transistor is connected via a serial LC circuit to the load, and connected via a large L inductor to the supply voltage.

The supply voltage is connected to ground via a large capacitor to prevent any RF signals leaking into the supply. The class-E amplifier adds a C capacitor between the transistor and ground and uses a defined L 1 to connect to the supply voltage. The following description ignores DC, which can be added easily afterwards. The above mentioned C and L are in effect a parallel LC circuit to ground. When the transistor is on, it pushes through the serial LC circuit into the load and some current begins to flow to the parallel LC circuit to ground.

Then the serial LC circuit swings back and compensates the current into the parallel LC circuit. At this point the current through the transistor is zero and it is switched off. Both LC circuits are now filled with energy in C and L 0.

The whole circuit performs a damped oscillation. The damping by the load has been adjusted so that some time later the energy from the Ls is gone into the load, but the energy in both C 0 peaks at the original value to in turn restore the original voltage so that the voltage across the transistor is zero again and it can be switched on. With load, frequency, and duty cycle 0. The class-E amplifier takes the finite on resistance into account and tries to make the current touch the bottom at zero.

This means that the voltage and the current at the transistor are symmetric with respect to time. The Fourier transform allows an elegant formulation to generate the complicated LC networks and says that the first harmonic is passed into the load, all even harmonics are shorted and all higher odd harmonics are open.

Class E uses a significant amount of second-harmonic voltage. The second harmonic can be used to reduce the overlap with edges with finite sharpness. For this to work, energy on the second harmonic has to flow from the load into the transistor, and no source for this is visible in the circuit diagram.

In reality, the impedance is mostly reactive and the only reason for it is that class E is a class F see below amplifier with a much simplified load network and thus has to deal with imperfections. In many amateur simulations of class-E amplifiers, sharp current edges are assumed nullifying the very motivation for class E and measurements near the transit frequency of the transistors show very symmetric curves, which look much similar to class-F simulations.

The class-E amplifier was invented in by Nathan O. Sokal and Alan D. Sokal, and details were first published in Experiment shows that a square wave can be generated by those amplifiers. Theoretically square waves consist of odd harmonics only. In a class-D amplifier, the output filter blocks all harmonics; i. So even small currents in the harmonics suffice to generate a voltage square wave. The current is in phase with the voltage applied to the filter, but the voltage across the transistors is out of phase.

Therefore, there is a minimal overlap between current through the transistors and voltage across the transistors. The sharper the edges, the lower the overlap. While in class D, transistors and the load exist as two separate modules, class F admits imperfections like the parasitics of the transistor and tries to optimise the global system to have a high impedance at the harmonics.

Of course there has to be a finite voltage across the transistor to push the current across the on-state resistance. Because the combined current through both transistors is mostly in the first harmonic, it looks like a sine.

That means that in the middle of the square the maximum of current has to flow, so it may make sense to have a dip in the square or in other words to allow some overswing of the voltage square wave. A class-F load network by definition has to transmit below a cutoff frequency and reflect above.

Any frequency lying below the cutoff and having its second harmonic above the cutoff can be amplified, that is an octave bandwidth. On the other hand, an inductive-capacitive series circuit with a large inductance and a tunable capacitance may be simpler to implement. By reducing the duty cycle below 0. The voltage square waveform degrades, but any overheating is compensated by the lower overall power flowing. Any load mismatch behind the filter can only act on the first harmonic current waveform, clearly only a purely resistive load makes sense, then the lower the resistance, the higher the current.

Class F can be driven by sine or by a square wave, for a sine the input can be tuned by an inductor to increase gain. If class F is implemented with a single transistor, the filter is complicated to short the even harmonics.

All previous designs use sharp edges to minimise the overlap. There are a variety of amplifier designs that enhance class-AB output stages with more efficient techniques to achieve greater efficiencies with low distortion. These designs are common in large audio amplifiers since the heatsinks and power transformers would be prohibitively large and costly without the efficiency increases.

The terms "class G" and "class H" are used interchangeably to refer to different designs, varying in definition from one manufacturer or paper to another. Class-G amplifiers which use "rail switching" to decrease power consumption and increase efficiency are more efficient than class-AB amplifiers. These amplifiers provide several power rails at different voltages and switch between them as the signal output approaches each level. Thus, the amplifier increases efficiency by reducing the wasted power at the output transistors.

Class-H amplifiers take the idea of class G one step further creating an infinitely variable supply rail. This is done by modulating the supply rails so that the rails are only a few volts larger than the output signal at any given time. The output stage operates at its maximum efficiency all the time.

Switched-mode power supplies can be used to create the tracking rails. Significant efficiency gains can be achieved but with the drawback of more complicated supply design and reduced THD performance. In common designs, a voltage drop of about 10V is maintained over the output transistors in Class H circuits.

The picture above shows positive supply voltage of the output stage and the voltage at the speaker output. The boost of the supply voltage is shown for a real music signal. The voltage signal shown is thus a larger version of the input, but has been changed in sign inverted by the amplification.

Other arrangements of amplifying device are possible, but that given that is, common emitter, common source or common cathode is the easiest to understand and employ in practice. If the amplifying element is linear, the output is a faithful copy of the input, only larger and inverted. In practice, transistors are not linear, and the output only approximates the input. The diagrams omit the bias circuits for clarity.

Any real amplifier is an imperfect realization of an ideal amplifier. An important limitation of a real amplifier is that the output it generates is ultimately limited by the power available from the power supply. An amplifier saturates and clips the output if the input signal becomes too large for the amplifier to reproduce or exceeds operational limits for the device.

The Doherty, a hybrid configuration, is receiving new attention. It was invented in by William H. The Doherty amplifier consists of a class-B primary or carrier stages in parallel with a class-C auxiliary or peak stage. The input signal splits to drive the two amplifiers, and a combining network sums the two output signals. Phase shifting networks are used in inputs and outputs. During periods of low signal level, the class-B amplifier efficiently operates on the signal and the class-C amplifier is cutoff and consumes little power.

During periods of high signal level, the class-B amplifier delivers its maximum power and the class-C amplifier delivers up to its maximum power. Perhaps, the ultimate refinement was the screen-grid modulation scheme invented by Joseph B. The Sainton amplifier consists of a class-C primary or carrier stage in parallel with a class-C auxiliary or peak stage. The stages are split and combined through degree phase shifting networks as in the Doherty amplifier.

The unmodulated radio frequency carrier is applied to the control grids of both tubes. Carrier modulation is applied to the screen grids of both tubes. As both tubes operate in class C, a significant improvement in efficiency is thereby achieved in the final stage. In addition, as the tetrode carrier and peak tubes require very little drive power, a significant improvement in efficiency within the driver stage is achieved as well C, et al.

Previous Continental Electronics designs, by James O. Weldon and others, retained most of the characteristics of the Doherty amplifier but added screen-grid modulation of the driver B, et al. The Doherty amplifier remains in use in very-high-power AM transmitters, but for lower-power AM transmitters, vacuum-tube amplifiers in general were eclipsed in the s by arrays of solid-state amplifiers, which could be switched on and off with much finer granularity in response to the requirements of the input audio.

However, interest in the Doherty configuration has been revived by cellular-telephone and wireless-Internet applications where the sum of several constant envelope users creates an aggregate AM result. The main challenge of the Doherty amplifier for digital transmission modes is in aligning the two stages and getting the class-C amplifier to turn on and off very quickly.

Recently, Doherty amplifiers have found widespread use in cellular base station transmitters for GHz frequencies. Implementations for transmitters in mobile devices have also been demonstrated. Various newer classes of amplifier, as defined by the technical details of their topology, have been developed on the basis of previously existing operating classes.

It had some elements in common with a current dumping design. It comprises a class A input stage coupled to a class B output stage, with a specific feedback design. Technics used a modified design in their class AA marketed output stage. This new class T is a revision of the common class-D amplifier, but with changes to ensure fidelity over the full audio spectrum, unlike traditional class-D designs.

It operates at different frequencies depending on the power output, with values ranging from as low as kHz to 1. Some Kenwood Recorder use class-W amplifiers. For special purposes, other active elements have been used. For example, in the early days of the satellite communication, parametric amplifiers were used. The core circuit was a diode whose capacity was changed by an RF signal created locally. Under certain conditions, this RF signal provided energy that was modulated by the extremely weak satellite signal received at the earth station.

The practical amplifier circuit to the right could be the basis for a moderate-power audio amplifier. Bipolar transistors are shown, but this design would also be realizable with FETs or valves. The input signal is coupled through capacitor C1 to the base of transistor Q1. The capacitor allows the AC signal to pass, but blocks the DC bias voltage established by resistors R1 and R2 so that any preceding circuit is not affected by it. Q1 and Q2 form a differential amplifier an amplifier that multiplies the difference between two inputs by some constant , in an arrangement known as a long-tailed pair.

This arrangement is used to conveniently allow the use of negative feedback, which is fed from the output to Q2 via R7 and R8. The negative feedback into the difference amplifier allows the amplifier to compare the input to the actual output. The amplified signal from Q1 is directly fed to the second stage, Q3, which is a common emitter stage that provides further amplification of the signal and the DC bias for the output stages, Q4 and Q5.

R6 provides the load for Q3 A better design would probably use some form of active load here, such as a constant-current sink. So far, all of the amplifier is operating in class A. They provide the majority of the current amplification while consuming low quiescent current and directly drive the load, connected via DC-blocking capacitor C2.

The diodes D1 and D2 provide a small amount of constant voltage bias for the output pair, just biasing them into the conducting state so that crossover distortion is minimized. That is, the diodes push the output stage firmly into class-AB mode assuming that the base-emitter drop of the output transistors is reduced by heat dissipation. This design is simple, but a good basis for a practical design because it automatically stabilises its operating point, since feedback internally operates from DC up through the audio range and beyond.

Further circuit elements would probably be found in a real design that would roll off the frequency response above the needed range to prevent the possibility of unwanted oscillation.

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Non investing amplifier microphone stand This is directly related to the second phenomenon: the waveform on the center frequency becomes less distorted. This is called crossover distortion. For this project a quite large piezo disk should be used 30 mm diameter or so and a weight should be glued with silicon compound to the upperside of the disk. Bipolar transistors are shown, but this design would also be realizable with FETs or valves. When the transistor is on, it pushes through the serial LC circuit into the load and some current begins non investing amplifier microphone stand flow to non investing amplifier microphone stand parallel LC circuit to ground. For special purposes, other active elements have been used. Any frequency lying below the cutoff and having its second harmonic above the cutoff can be amplified, that is an octave bandwidth.
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Physics 2nd Year - Chapter # 18 - Electronics - Operational Amplifier As Inverting And Non Inverting

The input voltage V1 is applied on the non-inverting pin of the op-amp. The op-amp based microphone amplifier circuit is shown below. C3 is used to filter VCC from the non inverting input of U1B and allow only the voltage changes of MIC1 ยท Since all this voltage difference will. The decision was made to contruct a non inverting amplifier with a gain of 10, For now the potentiometer acts as a stand-in for the DAC.