GB2429350A - An audio valve amplifier with a cascode input circuit - Google Patents

An audio valve amplifier with a cascode input circuit Download PDF

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Publication number
GB2429350A
GB2429350A GB0503798A GB0503798A GB2429350A GB 2429350 A GB2429350 A GB 2429350A GB 0503798 A GB0503798 A GB 0503798A GB 0503798 A GB0503798 A GB 0503798A GB 2429350 A GB2429350 A GB 2429350A
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GB
United Kingdom
Prior art keywords
amplifier
triode
circuit
input
tone
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.)
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Application number
GB0503798A
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GB0503798D0 (en
Inventor
Dennis William Marshall
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Individual
Original Assignee
Individual
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Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to GB0503798A priority Critical patent/GB2429350A/en
Publication of GB0503798D0 publication Critical patent/GB0503798D0/en
Publication of GB2429350A publication Critical patent/GB2429350A/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/22—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with tubes only
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10H—ELECTROPHONIC MUSICAL INSTRUMENTS; INSTRUMENTS IN WHICH THE TONES ARE GENERATED BY ELECTROMECHANICAL MEANS OR ELECTRONIC GENERATORS, OR IN WHICH THE TONES ARE SYNTHESISED FROM A DATA STORE
    • G10H3/00—Instruments in which the tones are generated by electromechanical means
    • G10H3/12—Instruments in which the tones are generated by electromechanical means using mechanical resonant generators, e.g. strings or percussive instruments, the tones of which are picked up by electromechanical transducers, the electrical signals being further manipulated or amplified and subsequently converted to sound by a loudspeaker or equivalent instrument
    • G10H3/14—Instruments in which the tones are generated by electromechanical means using mechanical resonant generators, e.g. strings or percussive instruments, the tones of which are picked up by electromechanical transducers, the electrical signals being further manipulated or amplified and subsequently converted to sound by a loudspeaker or equivalent instrument using mechanically actuated vibrators with pick-up means
    • G10H3/18—Instruments in which the tones are generated by electromechanical means using mechanical resonant generators, e.g. strings or percussive instruments, the tones of which are picked up by electromechanical transducers, the electrical signals being further manipulated or amplified and subsequently converted to sound by a loudspeaker or equivalent instrument using mechanically actuated vibrators with pick-up means using a string, e.g. electric guitar
    • G10H3/186—Means for processing the signal picked up from the strings
    • G10H3/187—Means for processing the signal picked up from the strings for distorting the signal, e.g. to simulate tube amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/08—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements
    • H03F1/22—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements by use of cascode coupling, i.e. earthed cathode or emitter stage followed by earthed grid or base stage respectively
    • H03F1/24—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements by use of cascode coupling, i.e. earthed cathode or emitter stage followed by earthed grid or base stage respectively in discharge-tube amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/181—Low-frequency amplifiers, e.g. audio preamplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G5/00—Tone control or bandwidth control in amplifiers
    • H03G5/02—Manually-operated control
    • H03G5/025—Equalizers; Volume or gain control in limited frequency bands
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G5/00—Tone control or bandwidth control in amplifiers
    • H03G5/02—Manually-operated control
    • H03G5/04—Manually-operated control in untuned amplifiers
    • H03G5/06—Manually-operated control in untuned amplifiers having discharge tubes
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10H—ELECTROPHONIC MUSICAL INSTRUMENTS; INSTRUMENTS IN WHICH THE TONES ARE GENERATED BY ELECTROMECHANICAL MEANS OR ELECTRONIC GENERATORS, OR IN WHICH THE TONES ARE SYNTHESISED FROM A DATA STORE
    • G10H2210/00—Aspects or methods of musical processing having intrinsic musical character, i.e. involving musical theory or musical parameters or relying on musical knowledge, as applied in electrophonic musical tools or instruments
    • G10H2210/155—Musical effects
    • G10H2210/311—Distortion, i.e. desired non-linear audio processing to change the tone color, e.g. by adding harmonics or deliberately distorting the amplitude of an audio waveform

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Multimedia (AREA)
  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Signal Processing (AREA)
  • Acoustics & Sound (AREA)
  • Amplifiers (AREA)

Abstract

An audio amplifier, which may be used with an electric guitar, has a preamplifier comprising a pair of triodes in a cascode connection for greater bandwidth and lower noise than a pentode preamplifier. Tone, drive, input impedance and output amplitude may be varied. A wireless remote controller for the amplifier is disclosed (figure 10). The amplifier may comprise a saturating drive circuit for the creation of "harmonic sustain" (figure 7). The resistor 41 may be of wirewound construction.

Description

1 mp1ifier 3 The present invention relates to an amplifier and in 4
particular to an amplifier for amplifying an audio signal which is the output of a pick-up from an electric or 6 semi-acoustic guitar.
8 In general, amplification is usually provided by either a 9 solid state integrated circuit or by a thermionic valve amplifier.
12 In the case of valve amplifiers, particularly those for 13 use with guitars, the same basic circuit and the same 14 valve have been used for a number of years namely a single stage triode valve usually ECC83/12AX7. However 16 there is an inherent problem with this circuit in that a 17 loss of frequency response and dynamics occurs as the 18 guitar signal is amplified in the first stage of 19 amplification. In addition, there is noisy electron flow from the triode valve. To date it has always been 21 considered acceptable to compensate for this type of 22 signal loss at later stages in the circuit. However, 23 there is a fundamental degradation in the quality of the 1 output when part of the signal is lost during the first 2 amplification stage.
3 Accordingly, if it were possible to achieve more 4 efficient transfer of the signal during first stage amplification then improvements in the overall output 6 signal would arise.
8 In the 1950's manufacturers building valve radio 9 frequency receivers used a particular circuit called a cascode circuit to amplify high frequency signals. UK 11 Patent No. 993657 discloses a cascode circuit arrangement 12 for such high frequency receivers. However, the frequency 13 response of these valve radio frequency receivers is too 14 high thereby allowing interference from external RF sources. Circuits of this type are too sensitive for use 16 with a music output such as a guitar output which has a 17 peak to peak value of around lOOmV to 2V. A typical RF 18 aerial output is between 2 and lOmV. In addition, the 19 carbon resistors described in the RF circuit are too noisy.
22 It is an object of the present invention to provide an 23 improved amplifier.
In accordance with the first aspect of the invention here 26 is provided an amplifier for amplifying an audio signal, 27 the amplifier comprising: 28 an input; 29 an output; and amplification means comprising a first triode and a 31 second triode, the input being connected to the grid of 32 the first triode to amplify the input signal; 1 the plate of the first triode being connected to the 2 cathode of the second triode; and a bias point connected 3 to the grid of the second triode; 4 wherein the bias point is held at a substantially constant voltage and wherein the amplified output of the 6 first triode drives the amplification of the second 7 triode to produce an amplified output.
9 The triode acts as a cascode operable at audio frequencies providing a very low noise output.
12 The use of back to back connected triode valves allows 13 the amplifier of the present invention to mimic the 14 performance of a pentode valve and accordingly removes the miller capacitances which would cause treble response 16 of a triode amplifier to be attenuated at frequencies of 17 greater than 12 1KHz.
19 The arrangement provided in the present invention differs from a pentode valve per se because it has a very low 21 noise output.
23 Substantially all of the gain in the circuit can be 24 provided by the triode amplification means.
26 Preferably, the bias point is coupled to a resistor.
28 Preferably, the output of the second triode is coupled to 29 a load resistor.
31 Preferably, the output of the second triode is coupled to 32 a capacitor and variable resistor connected to a 33 switching means.
2 Preferably, the amplifier of the present invention 3 further comprises a variable impedance matching circuit 4 connected between the input and the grid of the first triode.
7 Preferably, the variable impedance matching circuit 8 comprises at least one variable resistor connected across 9 the input.
11 Preferably, the amplifier further comprises a tone 12 control circuit.
14 Preferably, the tone control circuit is provided with a plurality of frequency filters designed to allow the 16 alteration of the frequency response of the input signal.
18 Preferably, the frequency filter is provided with a 19 plurality of serially connected capacitors connected to one or more variable resistors.
22 Preferably, the tone circuit separates out frequency 23 ranges from the input audio signal such that frequencies 24 in said ranges are transmitted through the tone control circuit in parallel.
27 Preferably, the tone control circuit is provided with a 28 relay coupled to one or more capacitors, the relay 29 functioning to shift the frequency range of the one or more of the frequency filters.
32 Optionally the frequency shift is 150 Hz.
1 Preferably, the amplifier further comprises a drive 2 circuit for creation of harmonic sustain in the 3 amplifier.
Preferably, the drive circuit comprise a dc blocker.
7 Preferably, the drive circuit further comprises one or 8 more triode circuits adapted to saturate the input 9 signal.
11 Preferably, the amplifier of the first aspect of the 12 invention is a pre-amplifier.
14 Preferably, the amplifier is suitable for use with an electric guitar.
17 Preferably, the variable impedance matching circuit has 18 components selected to be suitable for impedance matching 19 the input signal from a guitar pick-up.
21 Preferably, the amplifier further comprises control 22 means.
24 Preferably, the control means is capable of controlling the drive and/or tone of the amplifier.
27 Preferably, the control means further controls the 28 overall signal output of the amplifier.
Preferably, the control means is operatively connected to 31 a power amplifier.
1 Preferably, the control means is wirelessly coupled to 2 the amplifier.
4 Optionally, the control means is coupled to the amplifier by means of a wire.
7 The present invention will now be described by way of 8 example only, with reference to the accompanying drawings 9 in which: 12 Figure 1 is a block diagram of an amplifier in accordance 13 with the present invention; Figure 2 is a block diagram of the preamplifier used in 16 an amplifier in accordance with the present invention; 18 Figure 3 is a circuit diagram of the preamplifier used in 19 accordance with the present invention; 21 Figure 4 is a circuit diagram of an example of an 22 impedance dynamic control circuit used in accordance with 23 the present invention; Figure 5 is a circuit diagram showing the back to back 26 triode arrangement used in accordance with the present 27 invention; 29 Figure 6 is a circuit diagram of a tone circuit used in accordance with the present invention; 32 Figure 7 is a circuit diagram of a drive circuit used in 33 accordance with the present invention; 2 Figure 8 is a circuit diagram of a second embodiment of a 3 tone circuit used in accordance with the present 4 invention; 6 Figure 9 is a circuit diagram of a switch circuit used in 7 accordance with the present invention; 9 Figure 10 is a circuit diagram of a telemetry circuit used in accordance with the present invention; and 12 Figure 11 is a circuit diagram of a power circuit used in 13 accordance with the present invention.
Figure 1 shows the amplifier arrangement 1 having a power 16 source 3, a switching circuit 5, a telemetry circuit 7 17 and a preamplifier 9. The preamplifier contains an 18 impedance dynamic control 11 coupled to amplification 19 means 13 which is connected via a switch to a tone control circuit 15 and to a drive control circuit 17.
21 Switches are provided to allow the signal out of the 22 amplification means to bypass both the tone control 15 23 and the drive circuit 17.
Figure 2 shows the preamplifier 9 and provides more 26 information on the function of each of the components 27 previously referred to with reference to figure 1.
29 The impedance dynamic control is provided with a variable resistor circuit 19. The amplification means 13 is 31 provided with a first triode 21 and a second triode 23 32 which are coupled in a back to back arrangement. The tone 33 control 15 includes signal filtration means 24, 25, 27 1 and 29 that allows the base signal, the mid-signal, the 2 treble signal and the high frequency signal respectively 3 to be filtered. The drive circuit 17 is used to drive the 4 output from the amplifier or the amplifier and tone control circuit to be driven to saturation. Accordingly 6 this circuit includes a DC filter 31 and two triodes 33 7 and 35.
9 Details of this example of the present invention will now be provided with reference to figures 3 to 7.
12 Figure 3 shows the overall preamplifier circuit used in 13 accordance with the present invention and figures 4 to 7 14 show various parts of this circuit separated out for the sake of clarity.
17 Figures 3 and 4 show the input 37 to the preamplifier and 18 the impedance dynamic control circuit 11 which consists 19 of a variable resistor 39 in series with a second resistor. The impedance dynamic control 11 is used to 21 allow the impedance of the input signal from, for example 22 a magnetic guitar pickup, to be matched with the 23 impedance of the circuit. Typically, the input impedance 24 from a guitar pick-up will be in the range 250-400 kQ.
Circuit 11 is capable of reducing the input impedance to 26 around 10 kO. Having matched impedance allows the power 27 output of the circuit to be opt.imised.
29 Figures 3 and 5 show the cascode/triode circuit. This circuit contains a pair of triodes 21 and 23. The grid of 31 triode 21 receives the input from the impedance dynamic 32 control circuit 11. The output cathode of triode 21 is 33 fed into the anode of the triode 23. Amplification of the 1 input signal by triode 21 drives the triode 23. In 2 addition by holding the bias point 43 at a fixed voltage 3 a larger voltage swing is created across the wire wound 4 load resistor 41. This produces an extremely low noise output signal, the qualities of which are enhanced by use 6 of a wire-wound resistor which further reduces the noise 7 of the amplified signal and produces an inductive effect 8 which smoothes' the sound output from the amplifier.
9 The output at this stage is l2OV peak-to-peak.
11 Advantageously all of the amplification of the input 12 signal occurs by means of the cascode circuit 13 incorporating the triodes 21 and 23. The remaining 14 circuitry contained within the preamplifier is used to modify this signal and the overall attenuated output from 16 the preamplifier circuit has a voltage output of around 17 20 volts peak-to-peak.
19 Figures 3 and 6 show an embodiment of a tone circuit used in accordance with the present invention. The tone 21 circuit 15 comprises filter capacitors 47, 49, 51 and 54 22 which are combined with other components such as inductor 23 56 to create a series of frequency filters. These filters 24 are connected across variable resistors 59, 61, 63 and 65 to produce high frequency tone control 59, treble tone 26 control 61, mid-range tone control 63 and bass tone 27 control 65.
29 In addition switch 53 can be used to couple additional capacitors 55 into the circuit which shifts the mid-range 31 frequency band by 150 Hz. This circuit provides parallel 32 paths for different parts of the sound spectrum.
1 Figures 3 and 7 show the drive circuit 17 used in this 2 example of the present invention. The drive circuit is 3 used to saturate the amplified signal and comprises DC 4 blocking circuitry 73 comprising a resistor plus capacitor combination. The input level control 79 is 6 coupled to a pair of high gain triodes 75 and 77.
8 Figure 8 is an alternative embodiment of the tone 9 circuit. In this example a more sophisticated mid-range shifting switch is provided using a relay attached to 11 capacitors. In addition the filtering capacitors are 12 coupled to circuit lmQ resistors 95.
14 Figure 9 shows the switching circuit comprising transformers 99 and 101 along with triodes valves 103, 16 105, 109 and 111. Output 113 is situated to the left of 17 the diagram. The gain of the above circuit is 20. In an 18 alternative circuit, the gain can be increased to 50 to 19 allow the device to be used with a wider range of external effects units.
22 Figure 10 shows a telemetry system whereby the amplifier 23 of the present invention may be controlled via a wireless 24 link. The loop switch, tone, block switch and drive block switch 117, 119 and 121 respectively are shown in figure 26 10.
28 Figure 11 shows a suitable circuit 3 for use in 29 accordance with the present invention.
31 Advantageously the present invention provides a circuit 32 with an extremely low noise output signal. In addition, 33 by providing substantially all of the amplification of 1 the input music signal at an initial stage using a 2 cascade circuit camprising a pair af back ta back 3 triades, the present inventian preserves the musical 4 features af the input signal cantained in the third ar higher harmanics af that signal. These signal subtleties 6 are very af ten remaved during amplificatian when using 7 priar art amplifiers.
9 Impravements and madificatians maybe incarparated herein withaut deviating fram the scape af the inventian.

Claims (1)

1 Claims 3 1. An amplifier for amplifying an audio signal, the 4 amplifier
comprising: an input; 6 an output; and 7 amplification means comprising a first triode and a 8 second triode, the input being connected to the grid of 9 the first triode to amplify the input signal; the plate of the first triode being connected to the 11 cathode of the second triode; and a bias point connected 12 to the grid of the second triode; 13 wherein the bias point is held at a substantially 14 constant voltage and wherein the amplified output of the first triode drives the amplification of the second 16 triode to produce an amplified output.
18 2. An amplifier as claimed in claim 1 wherein, the bias 19 point is coupled to a resistor.
21 3. An amplifier as claimed in claim 1 or claim 2 22 wherein, the output of the second triode is coupled to a 23 load resistor.
4. An amplifier as claimed in any preceding claim 26 wherein, the output of the second triode is coupled to a 27 capacitor and variable resistor connected to a switching 28 means.
5. An amplifier as claimed in any preceding clai, 31 further comprising a variable impedance matching circuit 32 connected between the input and the grid of the first 33 triode.
2 6. An amplifier as claimed in claim 5 wherein, the 3 variable impedance matching circuit comprises at least 4 one variable resistor connected across the input.
6 7. An amplifier as claimed in any preceding claim 7 wherein, the amplifier further comprises a tone control 8 circuit.
8. An amplifier as claimed in claim 7 wherein, the tone 11 control circuit is provided with a plurality of frequency 12 filters designed to allow the alteration of the frequency 13 response of the input signal.
9. An amplifier as claimed in claim 8 wherein, the 16 frequency filter is provided with a plurality of serially 17 connected capacitors connected to one or more variable 18 resistors.
10. An amplifier as claimed in any of claims 7 to 9 21 wherein, the tone circuit separates out frequency ranges 22 from the input audio signal such that frequencies in said 23 ranges are transmitted through the tone control circuit 24 in parallel.
26 11. An amplifier as claimed in claims 7 to 10 wherein, 27 the tone control circuit is provided with a relay coupled 28 to one or more capacitors, the relay functioning to shift 29 the frequency range of the one or more of the frequency filters.
32 12. An amplifier as claimed in claim 11 wherein, the 33 frequency shift is 150 Hz.
2 13. An amplifier as claimed in any preceding claim, 3 further comprising a drive circuit for creation of 4 harmonic sustain in the amplifier.
6 14. An amplifier as claimed in claim 13 wherein, the 7 drive circuit comprise a dc blocker.
9 15. An amplifier as claimed in claim 13 or claim 14 wherein, the drive circuit further comprises one or more 11 triode circuits adapted to saturate the input signal.
13 16. An amplifier as claimed in any preceding claim 14 wherein the amplifier is a pre-amplifier.
16 17. An amplifier as claimed in any preceding claim 17 wherein, the amplifier is for use with an electric 18 guitar.
18. An amplifier as claimed in claim 5 wherein, the 21 variable impedance matching circuit has components 22 selected to be suitable for impedance matching the input 23 signal from a guitar pick-up.
19. An amplifier as claimed in any preceding claim 26 wherein, the amplifier further comprises control means.
28 20. An amplifier as claimed in claim 19 wherein, the 29 control means is capable of controlling the drive and/or tone of the amplifier.
1 21. An amplifier as claimed in claim 19 or claim 20 2 wherein, the control means further controls the overall 3 signal output of the amplifier.
22. An amplifier as claimed in any of claims 19 to 21 6 wherein, the control means is operatively connected to a 7 power amplifier.
9 23. An amplifier as claimed in any of claims 19 to 22 wherein, the control means is wirelessly coupled to the 11 amplifier.
13 24. An amplifier as claimed in any of claims 19 to 22 14 wherein, the control means is coupled to the amplifier by means of a wire.
GB0503798A 2005-02-24 2005-02-24 An audio valve amplifier with a cascode input circuit Withdrawn GB2429350A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0503798A GB2429350A (en) 2005-02-24 2005-02-24 An audio valve amplifier with a cascode input circuit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0503798A GB2429350A (en) 2005-02-24 2005-02-24 An audio valve amplifier with a cascode input circuit

Publications (2)

Publication Number Publication Date
GB0503798D0 GB0503798D0 (en) 2005-03-30
GB2429350A true GB2429350A (en) 2007-02-21

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB0503798A Withdrawn GB2429350A (en) 2005-02-24 2005-02-24 An audio valve amplifier with a cascode input circuit

Country Status (1)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0210155A2 (en) * 1985-07-25 1987-01-28 William Z. Johnson Cascode amplifier
US5450034A (en) * 1994-07-28 1995-09-12 Aphex Systems, Ltd. Reflected plate amplifier
US6737915B1 (en) * 2002-11-13 2004-05-18 Stephen Arthur Harner Tube input JFET output (TIJO) zero feedback audio amplifier

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0210155A2 (en) * 1985-07-25 1987-01-28 William Z. Johnson Cascode amplifier
US5450034A (en) * 1994-07-28 1995-09-12 Aphex Systems, Ltd. Reflected plate amplifier
US6737915B1 (en) * 2002-11-13 2004-05-18 Stephen Arthur Harner Tube input JFET output (TIJO) zero feedback audio amplifier

Also Published As

Publication number Publication date
GB0503798D0 (en) 2005-03-30

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