EP0082201A1 - Amplificateur de puissance capable de fonctionner simultanement dans deux classes - Google Patents

Amplificateur de puissance capable de fonctionner simultanement dans deux classes

Info

Publication number
EP0082201A1
EP0082201A1 EP82902403A EP82902403A EP0082201A1 EP 0082201 A1 EP0082201 A1 EP 0082201A1 EP 82902403 A EP82902403 A EP 82902403A EP 82902403 A EP82902403 A EP 82902403A EP 0082201 A1 EP0082201 A1 EP 0082201A1
Authority
EP
European Patent Office
Prior art keywords
amplifier
class
pair
clip
coupled
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP82902403A
Other languages
German (de)
English (en)
Inventor
Randall C. Smith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mesa Boogie Ltd
Original Assignee
Mesa Boogie Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mesa Boogie Ltd filed Critical Mesa Boogie Ltd
Publication of EP0082201A1 publication Critical patent/EP0082201A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/68—Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/26—Push-pull amplifiers; Phase-splitters therefor
    • H03F3/28—Push-pull amplifiers; Phase-splitters therefor with tubes only
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/541—Transformer coupled at the output of an amplifier

Definitions

  • Class A Triode operation is well known to dis ⁇ criminating audiophiles because of its characteristic usicality and "warmth". This warmth of tonality can be ascribed to the avoidance of crossover distortion (because in a push-pull configuration neither device ever approaches cut-off) and to the soft or gradual onset of clip when dynamic levels exceed available undistorted power capability. Un ⁇ notably, these-virtues of Triode Class A operation carry with them severe penalties of economy, efficiency and low power capability. Operating Class A means that less than half the supply power available can be converted to useful work, and that the devices themselves must be de-rated due to high zero-signal current draw. Connecting the screen grid of a Pentode to its plate, causing it to operate as a Triode, further reduces potential power gain by about half.
  • the present invention deals with output power amplification and the inherent distortion characteristics of different circuit configurations.
  • Music is by nature a series of transient and fleeting events.
  • the attack of any given musical note is of particular concern to the musician (as well as the listener) and much of a player's learned technique and expression revolves around the attack of the note.
  • Such is clearly the case with all stringed instruments—including piano— s well as reed, brass and percussion instruments.
  • the manner in which an audio amplifier handles these transient attacks is the single most important factor that distinguishes an outstanding amplifier from one which is merely acceptable in both reproduction and live performance applications.
  • Triode Class A circuit produces no crossover distortion and has a "soft" clip. • The sound of amplifier distortion at clip and beyond is almost unnoticeable because clip does not occur suddenly, and when it does, it is characterized by the predominance of even order products which are actually harmonious musically (that is consonant, not dissonant) to the fundamental. But the penalty is power. Such a circuit is expensive and inefficient.
  • This second pair of tubes (V7 and V8) operate as push-pull Pentodes Class AB (or B) .
  • the fixed bias being substantially greater than that for the Triode pair, allows use of much higher plate voltage while still observing safe levels of dissipation. Further, the fact that these devices are Pentodes, renders the available power gain even greater.
  • Signal drive and grid bias for the two pairs are distributed through a divider network adjusted for optimum balance. Such a balance can be achieved so that the net composite operation retains the virtues of both types of
  • SUBSTITUTE SHEET ⁇ V-ZIP 4 device Triode and Pentode
  • Class A and Class AB classes of operation
  • the Triode factor contributes the characteristic of soft, gradual clip which can be made to occur in advance of and to predominate over the clip of the Pentodes at all power levels.
  • the circuit enjoys the benefits of high power and efficiency contributed by the Pentodes running Class AB (or even Class B) but has the preferred distortion characteristics —clip and crossover-of Triodes run Class A. Usable tube life is also extended in an amplifier operating simultaneously in different classes because the Class AB Pentodes can be biased very high—into Class B— for cool low current, high power operation, while deterioration of the Class A Triodes results in very little sonic degradation since their power contribution is small.
  • a pair of Class A Triode input devices serves the twofold purposes of ampli ⁇ fying the incoming signal and splitting it into two phase inverted components. Excellent linearity and accurate phase inversion are accomplished by using a differentiating ampli ⁇ bomb pair whose cathodes are biased through a constant current device.
  • the first triode (VI) operates conventionally with • its grid serving as the input element and its plate furnishing the output.
  • the second triode (V2) derives its signal input from its shared cathode configuration with VI.
  • V2 The grid of V2 is grounded (or held slightly above ground to allow the injection of negative feedback) and amplified phase inverted output (with respect to output at the plate of VI) is present at V2's plate.
  • amplified phase inverted output (with respect to output at the plate of VI) is present at V2's plate.
  • the use of a constant current source in the common cathode circuit greatly helps to insure linearity of VI-V2 over a wide range of operating conditions.
  • a user operable switch means is provided to allow selection of full
  • a dual buffer amplifier (V3 and V4) is used to provide sufficient drive amplitude for the amplifier output states.
  • Tubes V3 and V4 are, as usual, operated as Class A Triodes but their common cathodes are carefully biased to maximize one of the effects of simultaneous operation in different classes: soft and gradual clipping.
  • the plate loading and cathode biasing of V3-V4 is carefully configured so that the onset of clip at V3-V4 is soft and occurs slightly before clip occurs in the amplifier output stages.
  • Capacitors with large values are often used in audio preampli ⁇ bomb circuits to allow linear frequency response down to 20 Hz or below.
  • circuit designer who is aware of the negative consequences of large capacitor values
  • phase shift or time delay
  • a differential amplifier has a constant current cathode source and acts as phase inverter/first amplifier followed by 2; a dual buffer amplifier whose loading and biasing are arranged to produce clip in a controlled fashion in harmony with 3; a pair of parallel output power amplifiers working simultaneously and in differing classes of operation whose outputs are combined. 4. Negative feedback may be applied selectively: full loop, local or avoided entirely. 5. To provide low frequency linearity while still ensuring faithful AC and DC response in the time domain, large coupling capacitors are arranged throughout in such a fashion that the impedance at their inputs is fairly low while the impedance at their outputs is very high. BRIEF DESCRIPTION OF THE DRAWING
  • the drawing shows a schematic diagram of an amplifier circuit in accordance with the present invention.
  • the input 1 is connected to the grid 3 of- VI via conductor 2.
  • Grid leak resistor 14 is connected to ground 25.
  • the cathode 5 of VI is tied directly to the cathode 6 of V2 and both are energized from a negative B- source 12.
  • Use of a constant-current source device 11 in the cathode circuit accomplishes vastly improved linearity of VI and V2 under widely ranging operating conditions.
  • As VI amplifies signal fluctuations which appear on its cathode 5 also appear on the cathode 6 of V2 and are used to drive V2.
  • the grid 4 of V2 is for all intents and purposes grounded although a small resistor 13 may be used to allow the injecrion of negative feedback to the grid 4 via an RC network 15, 16.
  • a switch means 91 is then provided to select negative feedback origin ⁇ ating locally from the output of buffer stage V3 through a blocking capacitor 96 and a series resistor 93. Or as alternatives to suit program material, choice of speaker and listener preference, switch 91 can- also be used to select overall negative feedback, which signal would derive from a point 95 at the amplifier output and be buffered through resistor 92. As the third alternate, the switch 91 offers the
  • Cathodes 27, 28 of V3 and V4 respectively are energized through resistor 26 whose value is selected in conjunction with the values of loading resistors 35, 36 to cause a soft and gradual clip of V3, V4 to occur just prior to the onset of clip in the Class A Triode section of the amplifier output state.
  • the plates 31, 32 of V3 and V4 are energized from the B+ high voltage supply 80 through resistors 33, 34. Output from the plates 31, 32 of V3 and V4 is coupled to the output stages through capacitors 37 and 38, both of which have a large value, and resistors 83 and 84 which are used to present a very high impedance to the output of capacitors 37 and 38.
  • Negative bias for the output stage comprised of V5, V6, V7 and V8 derives from a supply represented at 71.
  • This negative DC bias flows through an out ⁇ put tube balancing network comprised of potentiometer 69 and drain resistors 81 and 82.
  • Bias for the Pentodes V7 and V8 is obtained through low value resistors 43 and 44, and is maintained at a level that provides Class AB (or Class B) operation for these Pentodes.
  • Screen grids 61, 62 of these Pentodes (V7, V8) are fed from a high voltage supply 74 through low value resistors 63 and 64.
  • Pentode plates 59, 60 are impedance matched to the full primary winding 72 of the output transformer with one plate at each of the ends 87, 88.
  • the cathodes 67, 68 of V7 and V8 are selectively energized from ground 25 through a user operable switch means 70. When the switch is open, no current flows, V7 and V8 are effectively in a "standby" mode and the amplifier comprises functionally of the pair of Class A Triodes V5 and V6. With the switch 70 closed, the amplifier circuit comprising V7 and V8 (and any other number of Pentode AB output pairs in parallel) and their
  • SUBSTITUTE SHEET / tjfl 8 inclusive parts becomes operational and in fact contribute the vast majority of power to the common output 75 as the plates 59 and 60 of V7 and V8 are connected to the output transformer primary 72 through conductors 76 and 77.
  • Pentodes shown as V5 and V6 are made to function as Triodes because their plates 45, 46 are tied to their respective screen grids 51, 52 through low value resistors 53, 54.
  • Cathodes 57, 58 are energized from ground 25.
  • Grid bias on V5 and V6 is reduced to a low value compared to the AB Pentode pair by the divider networks com ⁇ prising resistors 39 and 41 for V5 and resistors 40 and 42 for V6.
  • the values selected for these divider net ⁇ works and other resistors in the bias network—as well as in the signal path—are chosen to cause the onset of clip in the Triode Class A pair to occur slightly before the Pentode AB * pair(s) begins to clip.
  • Taps 89, 90 can be provided at lower impedance points on the output transformer primary 72 to properly match the plate loads imposed by the Class A Triode pair.
  • Voltage dropping resistors 47 and 48 can be used to reduce dissipation of the plates 45, 46 of the Class A Triodes V5 and V6 to safe levels while still allowing the maintenance of full DC voltage on the Pentode pair V7, V8.
  • Bypass capaci ⁇ tors 49, 50 may be used to restore signal gain lost through the dropping resistors 47, 48.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Abstract

Un appareil d'amplification électronique est destiné à la reproduction du son et à une amplification d'un instrument de musique où deux amplificateurs parallèles (V5-V8), fonctionnant simultanément, chacun dans une classe différente de fonctionnement, sont alimentés à partir d'une seule source de signaux (V1-V4) et dont les sorties sont combinées. Dans le mode préférentiel de réalisation, au moins deux paires de tubes à vide push-pull sont requis et ils sont disposés de sorte qu'une paire (V5, V6) fonctionne comme une triode de la Classe A tandis que l'autre paire (V7, V8) (ou paire) fonctionne comme une pentode de la Classe AB (ou Classe B). Le circuit peut alors être optimalisé de sorte que les caractéristiques soniques désirables de fonctionnement de la triode de Classe A sont transmises à des pentodes de la Classe AB (ou Classe B) qui produisent réellement toute ou presque toute la puissance. La forme d'onde de la puissance de sortie possède la puissance élevée et le rendement caractéristique du fonctionnement de la pentode de Classe AB (ou Classe B) mais sans les effets secondaires sonores nuisibles, c'est-à-dire qu'il y a une absence totale de croisement ou distorsion à "entaille", ainsi qu'une attaque de crète graduelle "douce". Un commutateur arrêt/marche (70) peut également être utilisé pour donner davantage de flexibilité au système en ce qui concerne la disponibilité de la puissance et la performance sonores.
EP82902403A 1981-06-29 1982-06-28 Amplificateur de puissance capable de fonctionner simultanement dans deux classes Withdrawn EP0082201A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US27871781A 1981-06-29 1981-06-29
US278717 2002-10-22

Publications (1)

Publication Number Publication Date
EP0082201A1 true EP0082201A1 (fr) 1983-06-29

Family

ID=23066063

Family Applications (1)

Application Number Title Priority Date Filing Date
EP82902403A Withdrawn EP0082201A1 (fr) 1981-06-29 1982-06-28 Amplificateur de puissance capable de fonctionner simultanement dans deux classes

Country Status (4)

Country Link
EP (1) EP0082201A1 (fr)
CA (1) CA1180775A (fr)
IT (1) IT1196546B (fr)
WO (1) WO1983000265A1 (fr)

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2825766A (en) * 1955-06-30 1958-03-04 Mcintosh Lab Inc High fidelity audio amplifier
NL237518A (fr) * 1958-04-08

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8300265A1 *

Also Published As

Publication number Publication date
WO1983000265A1 (fr) 1983-01-20
IT8248709A0 (it) 1982-06-28
CA1180775A (fr) 1985-01-08
IT1196546B (it) 1988-11-16

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Legal Events

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PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

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Effective date: 19830829

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Inventor name: SMITH, RANDALL C.