Tube push pull amplifier distortion

Cite this Simulator:. Function generator, CRO, Regulated Power supply, pnp and npn transistors ,resistance, connecting wires. Push pull amplifier circuit design has been implemented on the virtual breadboard using following specifications:. A push-pull output is a type of electronic circuit that can drive either a positive or a negative current into a load.

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Content:

• Audio distortion and feedback
• Push pull amplifier
• Audio amplifier distortion and common improvement methods
• The Valve Wizard
• What is a Push-pull Amplifier : Circuit Diagram and Its Working Principle
• Tonal differences in the sound of power tube distortion in a single-ended amp vs a push-pull amp?
• The Red Light District: A 15W Push-Pull Amplifier

WATCH RELATED VIDEO: Power Amplifier (Part 5): Push Pull Class A Amplifier (Harmonic Distortion)

Audio distortion and feedback

A push—pull amplifier is a type of electronic circuit that uses a pair of active devices that alternately supply current to, or absorb current from, a connected load. This kind of amplifier can enhance both the load capacity and switching speed. Push—pull outputs are present in TTL and CMOS digital logic circuits and in some types of amplifiers , and are usually realized by a complementary pair of transistors , one dissipating or sinking current from the load to ground or a negative power supply, and the other supplying or sourcing current to the load from a positive power supply.

A push—pull amplifier is more efficient than a single-ended "class-A" amplifier. The output power that can be achieved is higher than the continuous dissipation rating of either transistor or tube used alone and increases the power available for a given supply voltage. Symmetrical construction of the two sides of the amplifier means that even-order harmonics are cancelled, which can reduce distortion. However, the push—pull amplifier requires a phase-splitting component that adds complexity and cost to the system; use of center-tapped transformers for input and output is a common technique but adds weight and restricts performance.

If the two parts of the amplifier do not have identical characteristics, distortion can be introduced as the two halves of the input waveform are amplified unequally.

Crossover distortion can be created near the zero point of each cycle as one device is cut off and the other device enters its active region. Push—pull circuits are widely used in many amplifier output stages. A pair of audion tubes connected in push—pull is described in Edwin H. Colpitts ' US patent granted in , although the patent does not specifically claim the push—pull connection. A digital use of a push—pull configuration is the output of TTL and related families.

The upper transistor is functioning as an active pull-up, in linear mode, while the lower transistor works digitally. For this reason they are not capable of sourcing as much current as they can sink typically 20 times less. Because of the way these circuits are drawn schematically, with two transistors stacked vertically, normally with a level shifting diode in between, they are called " totem pole " outputs. A disadvantage of simple push—pull outputs is that two or more of them cannot be connected together, because if one tried to pull while another tried to push, the transistors could be damaged.

To avoid this restriction, some push—pull outputs have a third state in which both transistors are switched off. In this state, the output is said to be floating or, to use a proprietary term, tri-stated. The alternative to a push—pull output is a single switch that connects the load either to ground called an open collector or open drain output or to the power supply called an open-emitter or open-source output.

A conventional amplifier stage which is not push—pull is sometimes called single-ended to distinguish it from a push—pull circuit. In analog push—pull power amplifiers the two output devices operate in antiphase i. The two antiphase outputs are connected to the load in a way that causes the signal outputs to be added, but distortion components due to non-linearity in the output devices to be subtracted from each other; if the non-linearity of both output devices is similar, distortion is much reduced.

Symmetrical push—pull circuits must cancel even order harmonics, like 2f, 4f, 6f and therefore promote odd order harmonics, like f, 3f, 5f when driven into the nonlinear range. A push—pull amplifier produces less distortion than a single-ended one. This allows a class-A or AB push—pull amplifier to have less distortion for the same power as the same devices used in single-ended configuration.

Class AB and class B dissipate less power for the same output than class A; distortion can be kept low by negative feedback and by biassing the output stage to reduce crossover distortion.

A class-B push—pull amplifier is more efficient than a class-A power amplifier because each output device amplifies only half the output waveform and is cut off during the opposite half.

It can be shown that the theoretical full power efficiency AC power in load compared to DC power consumed of a push—pull stage is approximately Power dissipation in the output devices is roughly one-fifth of the output power rating of the amplifier.

The output of the amplifier may be direct-coupled to the load, coupled by a transformer, or connected through a dc blocking capacitor. Where both positive and negative power supplies are used, the load can be returned to the midpoint ground of the power supplies. A transformer allows a single polarity power supply to be used, but limits the low-frequency response of the amplifier. Similarly, with a single power supply, a capacitor can be used to block the DC level at the output of the amplifier.

Where bipolar junction transistors are used, the bias network must compensate for the negative temperature coefficient of the transistors' base to emitter voltage. This can be done by including a small value resistor between emitter and output. Also, the driving circuit can have silicon diodes mounted in thermal contact with the output transistors to provide compensation.

It is now very rare to use output transformers with transistor amplifiers, although such amplifiers offer the best opportunity for matching the output devices with only PNP or only NPN devices required. Two matched transistors of the same polarity can be arranged to supply opposite halves of each cycle without the need for an output transformer, although in doing so the driver circuit often is asymmetric and one transistor will be used in a common-emitter configuration while the other is used as an emitter follower.

This arrangement is less used today than during the 's; it can be implemented with few transistors not so important today but is relatively difficult to balance and to keep a low distortion. This type of arrangement tends to give lower distortion than quasi-symmetric stages because even harmonics are cancelled more effectively with greater symmetry.

In the past when good quality PNP complements for high power NPN silicon transistors were limited, a workaround was to use identical NPN output devices, but fed from complementary PNP and NPN driver circuits in such a way that the combination was close to being symmetrical but never as good as having symmetry throughout.

Distortion due to mismatched gain on each half of the cycle could be a significant problem. Employing some duplication in the whole driver circuit, to allow symmetrical drive circuits can improve matching further, although driver asymmetry is a small fraction of the distortion generating process. Using a bridge-tied load arrangement allows a much greater degree of matching between positive and negative halves, compensating for the inevitable small differences between NPN and PNP devices.

The output devices, usually MOSFETs or vacuum tubes , are configured so that their square-law transfer characteristics that generate second-harmonic distortion if used in a single-ended circuit cancel distortion to a large extent. That is, as one transistor's gate-source voltage increases, the drive to the other device is reduced by the same amount and the drain or plate current change in the second device approximately corrects for the non-linearity in the increase of the first.

These tubes drive current through the two halves of the primary winding of a center-tapped output transformer. Signal currents add, while the distortion signals due to the non-linear characteristic curves of the tubes subtract. These amplifiers were first designed long before the development of solid-state electronic devices; they are still in use by both audiophiles and musicians who consider them to sound better. Because these are essentially square-law devices, the comments regarding distortion cancellation mentioned above apply to most push—pull tube designs when operated in class A i.

The output is taken from the cathode of the top not directly driven device, which acts part way between a constant current source and a cathode follower but receiving some drive from the plate anode circuit of the bottom device.

The drive to each tube therefore might not be equal, but the circuit tends to keep the current through the bottom device somewhat constant throughout the signal, increasing the power gain and reducing distortion compared with a true single-tube single-ended output stage.

White is similar to the SEPP design above, but the signal input is to the top tube, acting as a cathode follower, but one where the bottom tube in common cathode configuration if fed usually via a step-up transformer from the current in the plate anode of the top device.

It essentially reverses the roles of the two devices in SEPP. The bottom tube acts part way between a constant current sink and an equal partner in the push—pull workload. Again, the drive to each tube therefore might not be equal. A so-called ultra-linear push—pull amplifier uses either pentodes or tetrodes with their screen grid fed from a percentage of the primary voltage on the output transformer. This gives efficiency and distortion that is a good compromise between triode or triode-strapped power amplifier circuits and conventional pentode or tetrode output circuits where the screen is fed from a relatively constant voltage source.

From Wikipedia, the free encyclopedia. For other uses of "push—pull", see Push—pull. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Transformer coupled vacuum tube push-pull audio amplifier from The two triode output tubes are on right.

A Magnavox stereo tube push—pull amplifier, circa , utilizes two 6BQ5 output tubes per channel. The two pairs of push-pull tubes are visible in front of the output transformers. This section needs additional citations for verification. November Learn how and when to remove this template message. Fink, ed. Linear Audio. Retrieved 7 November Categories : Electronic circuits. Hidden categories: Articles needing additional references from November All articles needing additional references Articles needing additional references from November All articles with unsourced statements Articles with unsourced statements from December Namespaces Article Talk.

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Push pull amplifier

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Audio amplifier distortion and common improvement methods

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The Valve Wizard

The cross over distortion in class B power amplifier is eliminated by Class AB power amplifier which uses diodes at the bases of transistors to reduce forward bias voltage at bases, i. Start Learning English Hindi. This question was previously asked in. Attempt Online. Answer Detailed Solution Below Option 1 : crossover distortion.

What is a Push-pull Amplifier : Circuit Diagram and Its Working Principle

Welcome, Guest. Please login or register. Home Help Search Login Register. Pages: [ 1 ] 2 Go Down. I just wrapped up the electrical work on a tweed deluxe-ish build I P2P wired into an old Voycall intercom amp I picked up on eBay.

Tonal differences in the sound of power tube distortion in a single-ended amp vs a push-pull amp?

Push-pull stages are able to reduce harmonic distortions, specifically second order distortions, produced in the stage itself. When an input stage has a single-ended configuration and operates in non-linear areas, it produces distortions. If the distorted pre-amplified signal is given to a push-pull stage, its distortions are amplified as well. A technique to reduce distortions, across all amplifier stages, is the global negative feedback. The effect of the global negative feedback can be explained intuitively as follows.

The Red Light District: A 15W Push-Pull Amplifier

Effective date : Year of fee payment : 4. A power amplifier has a distortion control circuit responsive to a clipping detector for loading said amplifier input with a signal sufficient to reduce the input to the tube grids to a level below clipping.

Another series of tests were made on the same group of preamplifiers using a spectrum analyzer to measure the amplitude of individual harmonics. Every harmonic to the seventh was plotted. Since it is not possible to measure the relative phase of the harmonics on the spectrum analyzer, the over- load waveforms were recorded for Fourier analysis on the digital computer. The resulting plots divided amplifiers into three distinct categories.

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Power amps create harmonic distortion because of differences in amplification when operating in different regions of their characteristic curves. Single-ended amplifiers like the one shown here, generally create generous quantities of second harmonic distortion. The harmonic mix varies considerably depending on the DC operating point and the output transformer primary impedance, as can be seen in this example using a single-ended power pentode.