audio power amplifiers - leon audio · audio power amplifiers history and design of the audio...
TRANSCRIPT
![Page 1: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/1.jpg)
LVA EV
RHE CS E RA
Audio Power AmplifiersHistory and design of the audio amplifier
Graeme J Cohen AES Sept 25 2012
![Page 2: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/2.jpg)
Early High Quality Sound
![Page 3: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/3.jpg)
The Loftin-White circuit as it was publishedin Radio News issue January 1929
The Loftin-White amplifier
![Page 4: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/4.jpg)
![Page 5: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/5.jpg)
![Page 6: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/6.jpg)
![Page 7: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/7.jpg)
![Page 8: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/8.jpg)
1947 Earlier Williamson
![Page 9: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/9.jpg)
1947 Earlier Williamson. Loop gain and phase.
![Page 10: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/10.jpg)
1949 Williamson amplifier
![Page 11: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/11.jpg)
1949 Basic principles of McIntosh Amplifier
![Page 12: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/12.jpg)
1949 Complete 50 watt McIntosh amplifier
![Page 13: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/13.jpg)
Quality Sound 1950s
![Page 14: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/14.jpg)
1949 The Leak TL12
![Page 15: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/15.jpg)
1952 The Quad amplifier
![Page 16: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/16.jpg)
1957 Baxandall’s simple amplifier
![Page 17: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/17.jpg)
Circa 1959 Mullard 20W amplifier
![Page 18: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/18.jpg)
![Page 19: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/19.jpg)
Circa 1959 Mullard 3-3 (3 valves and 3 watts)
![Page 20: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/20.jpg)
Circa 1959 General Electric Class AB2 600-1100 watt amplifier.
![Page 21: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/21.jpg)
Guitar Amplifiers
![Page 22: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/22.jpg)
"Woodies" 1946
![Page 23: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/23.jpg)
Circa 1950's
![Page 24: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/24.jpg)
Circa 1950'sVOX AC30
![Page 25: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/25.jpg)
Early Solid State Amplifiers
![Page 26: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/26.jpg)
Circa 1953
![Page 27: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/27.jpg)
Circa 1954 30 Watts
![Page 28: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/28.jpg)
Circa 1958
![Page 29: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/29.jpg)
Sliding-bias Amplifier. Wireless World May 1962
INPUT
![Page 30: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/30.jpg)
“Modern” Solid State Amplifiers
![Page 31: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/31.jpg)
1968 Bailey
![Page 32: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/32.jpg)
April 1969 Linsley Hood Class A 10 watts
![Page 33: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/33.jpg)
1975 Marshall Leach. Low TIM amplifier
![Page 34: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/34.jpg)
Circa 1973 Blomley. New approach to Class B amplifier design.
![Page 35: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/35.jpg)
Circa 1975 Quad current dumping amplifier concept.
![Page 36: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/36.jpg)
1977 Siliconix VMOS power FET amplifier.
![Page 37: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/37.jpg)
![Page 38: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/38.jpg)
1986 G.J. Cohen
![Page 39: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/39.jpg)
![Page 40: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/40.jpg)
![Page 41: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/41.jpg)
1986 G.J. Cohen Prototype MOSFET amp for Adelaide Festival Centre (FESMOS)
Hinged upright for service
![Page 42: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/42.jpg)
1993 D. Self Current displacement amplifier
![Page 43: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/43.jpg)
“Other“Amplifiers
![Page 44: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/44.jpg)
Class D operation
Comparator
![Page 45: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/45.jpg)
1993 G.J. CohenTransmission line transformers. AES Preprint 3692
![Page 46: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/46.jpg)
1995 G.J. CohenDual Single Ended Amplifier. AES Preprint 4028
Linear OutputCurrent
Test Circuit
![Page 47: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/47.jpg)
1995 G.J. CohenDual Single Ended Amplifier.(Showing Distortion Reduction)
![Page 48: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/48.jpg)
1995 G.J. CohenDual Single Ended Amplifier.(Showing Distortion Reduction)
![Page 49: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/49.jpg)
Bipolar Characteristics
![Page 50: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/50.jpg)
MOSFET Characteristics
![Page 51: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/51.jpg)
Voltage Output Amplifier Current Output Amplifier
2010 E. MerilainenCurrent Driving of Loudspeakers
![Page 52: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/52.jpg)
2011 G.J. CohenValve - FET Amplifier
![Page 53: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/53.jpg)
1943 ZenithHearing Aid Amplifier
![Page 54: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/54.jpg)
2012 G.J. Cohen Headphone Amp
![Page 55: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/55.jpg)
LVA EV
R
HE CS E RA
Audio Power AmplifiersHistory and design of the audio amplifier
Graeme J Cohen AES Sept 25 2012
Early High Quality Sound
The Loftin-White circuit as it was published
The Loftin-White amplifier
in Radio News issue January 1929
Possibly earliest famous amp.Direct coupledPentode input, Triode outputMinimum Components
Pentode silvering from getterTriode: solid metal anodeHalf wave rectifier with mesh anode
F. Langford Smith presentationPentode input stageTriode and Pentode outputs1936 designs common in radios
F.E. Terman design 1937Pentode input, Triode outputCurrent feedback to I/P cathodeForerunner of later designs
1
![Page 56: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/56.jpg)
1947 Earlier Williamson
1947 Earlier Williamson. Loop gain and phase.
1949 Williamson amplifier
1949 Basic principles of McIntosh Amplifier
1949 Complete 50 watt McIntosh amplifier
2
Direct coupled push-pull designNeon tubes for voltage shiftCurrent feedbackVoltage and current output also usedfor analog computing
Early Williamson design 1947Triode connected P-P 807'sDC coupled input stage Minimal coupling capacitors
Wide response with no feedbackWell designed output transformerSmooth response with feedbackControlled phase shift with feedback
Later Williamson design 1949Triode connected push-pull KT66'sExtra compensation on input anodeExtra power supply filter choke
Also 600 ohms from cathodesFixed bias (maximum output)P-P feedback from cathodesPreamplifier built in
Bifilar and Trifilar windingsScreen grids connected to op. anodesCathode windingsDriver transformer for large swings
![Page 57: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/57.jpg)
Quality Sound 1950s
1949 The Leak TL12
1952 The Quad amplifier
1957 Baxandall’s simple amplifier
Circa 1959 Mullard 20W amplifier
Triode connected KT66's”Long tail” phase splitterSingle pentode input stageCompensation on feedback
Pentode Cathode windingsUnique Pentode phase splitter with screen grids coupled
connected KT66's
Pentode connected EL84'sHeavy decoupling of output screensFeedback from extra tap on O/P T/FDC Coupling of I/P with compensation
”Ultra Linear” connected O/P stagePentode input stages DC coupled to phase splitterMinimal coupling capacitors
”Ultra Linear” or distributed load
43% common. winding:- best
Triode: low power, low distortionPentode: max power, max distortion20% common. winding:- better
3
![Page 58: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/58.jpg)
Circa 1959 Mullard 3-3 (3 valves and 3 watts)
Circa 1959 General Electric Class AB2 600-1100 watt amplifier.
Guitar Amplifiers
"Woodies" 1946
Circa 1950's
Circa 1950'sVOX AC30
Class “AB2" operationAll stages triode connectedDriver T/F because of grid currentEqual turns on driver pri & sec with coupling caps. from cathodes to grids
Fender, “first” amplifier for guitars”Woodies” due to polished cabinetsInput mixing stage, simple splitterNo Feedback gives soft overload
Marshall, later & high powerMore complexVibrato/tremelo added
Vox, later designAlso complex additionsSome small sized models
Input Pentode, starvation condition gives maximum gainBoth stages DC coupledClass “A” operation, 3 watt output
4
![Page 59: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/59.jpg)
Early Solid State Amplifiers
Circa 1953
Circa 1954 30 Watts
Circa 1958
Sliding-bias Amplifier. Wireless World May 1962
INPUT
“Modern” Solid State Amplifiers
Germanium PNP Transistor 1953Interstage coupling transformersFour only capacitors of same valueTwo of 1.5 volt batteries (+/- supply!)
High power (30W) Germanium powerGrounded base stages, except input due to poor response of devicesTherefore coupling transformers
Germanium with better freq. responseCommon emitter stagesStill transformer coupledHigh gain, no feedback Commonly used in “Tranny” Radios
Class “A” low to high bias O/P stageBias increased for higher average signal. i.e. Low average dissipationPossibly for radio comms use
5
Brattain, Bardeen & Schockly invented the transistor in December 1947 at Bell Labs.
![Page 60: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/60.jpg)
1968 Bailey
April 1969 Linsley Hood Class A 10 watts
1975 Marshall Leach. Low TIM amplifier
Circa 1973 Blomley. New approach to Class B amplifier design.
Circa 1975 Quad current dumping amplifier concept.
1977 Siliconix VMOS power FET amplifier.
J.L. Hood 10 watt Class “A”NPN output transistors onlyVery high frequency driver transistors so loop gain less than unity at 180No crossover distortion
Low transient intermod. distortionFully complementary-symmetryD.C. coupled20dB or less feedbackRFI input protection
Single ended input current switched to P-P output current in class “B”Bipolar transistor true LOG operationThermal tracking of this function
QUAD unique current dumping amp.Class “A” at low level & Class “B” at high levels via feedback pathsThe four feedback components are a frequency dependant balanced bridge
Quasi-complimentary N-Channel VMOS only available at this timeHence current mirrors used for driveLow feedback approximately 20dB
Early use of symmetrical voltage railsEarly use of overload protectionEarly bias compensation on inputSymmetrical output stage and Zobel network
6
o
![Page 61: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/61.jpg)
1986 G.J. Cohen
1986 G.J. Cohen
Hinged upright for service
Prototype MOSFET amp for Adelaide Festival Centre (FESMOS)
1993 D. Self Current displacement amplifier
All FET design, used hybridSingle pole response (C1), gate cap.Modest feedbackBalanced input
Open loop -3dB to 40kHzClosed loop -3dB to ~150kHzOverall smooth responseResponse to DC. No coupling, feedback or bypass capacitors used
Hybrids with minimal ext. componentsUsed in FESMOS amplifiersEase of servicing (replace hybrids)
Prototype for FESMOS development500 watts per channelHeatsink folds up for servicing2RU for proto., Conv. cooling
Bias current change with signalSimilar but opposite to sliding-biasQuestion output current (bias) change under dynamic conditions
Low distortion from 40Hz - 20kHzOpen loop -3dB to 40kHzRFI input filter curve shown
7
![Page 62: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/62.jpg)
“Other“Amplifiers
Comparator
Class D operation
1993 G.J. CohenTransmission line transformers. AES Preprint 3692
1995 G.J. CohenDual Single Ended Amplifier. AES Preprint 4028
Linear OutputCurrent
Test Circuit
1995 G.J. CohenDual Single Ended Amplifier.(Showing Distortion Reduction)
1995 G.J. CohenDual Single Ended Amplifier.(Showing Distortion Reduction)
Class “D” efficient operationUses pulse width modulationLow pass filter before speakerPossible radiation of switching noise
Bifilar auto-transformer (No DC)Triode anode and cathode outputLower turns, tighter couplingTwo floating power supplies
2 single ended Class “A” per channelTest circuit to generate current O/P to compare P-P, and 2 Class “A”, added
Two single ended transformers showing some distortion reduction
8
Individual waveforms approaching overload Combined waveforms
![Page 63: Audio Power Amplifiers - Leon Audio · Audio Power Amplifiers History and design of the audio amplifier Graeme J Cohen AES Sept 25 2012 Early High Quality Sound The Loftin-White circuit](https://reader030.vdocuments.net/reader030/viewer/2022021602/5e7367a296bec97a6a0276de/html5/thumbnails/63.jpg)
Bipolar Characteristics
MOSFET Characteristics
Voltage Output Amplifier Current Output Amplifier
2010 E. MerilainenCurrent Driving of Loudspeakers
2011 G.J. CohenValve - FET Amplifier
1943 ZenithHearing Aid Amplifier
2012 G.J. Cohen Headphone Amp
Field Effect Transistor curvesGentle gradient, lower gainGradual turn-onReduced current with higher temp.Zero temperature coefficient at“A” to “AB” transition
Current drive to speakersPlus: holds current at resonanceMinus: has low damping for transientsSpeakers are usually designed for voltage (low impedance) drive
Valve input & driver with FET outputValves for voltage gainFETs for current gainValve amp with no O/P transformer2 coupling caps. Min. phase shiftNo bypass caps. in feedback path
1943 Hearing aid amplifierValves developed for this in 1942Inbuilt mic. above clip for coat pocketSeparate batteries and earpiece
Output impedance setable from one ohm up to 120 ohms (DIN Spec)Valves are low distortion types
Bipolar junction transistor curvesSteep gradient due to high gainHas sharp turn-on for voltage drivePossible thermal run-away
9