Guitar Amplifier

Guitar Amplifier

Circuit diagram:Parts:

P1______________4K7  Linear Potentiometer
P2_____________10K   Log. Potentiometer
R1,R2__________68K   1/4W Resistors
R3____________220K   1/4W Resistor
R4,R6,R11_______4K7  1/4W Resistors
R5_____________27K   1/4W Resistor
R7______________1K   1/4W Resistor
R8______________3K3  1/2W Resistor
R9______________2K   1/2W Trimmer Cermet
R10___________470R   1/4W Resistor
R12_____________1K5  1/4W Resistor
R13___________470K   1/4W Resistor
R14____________33K   1/4W Resistor 

C1____________100pF   63V Ceramic Capacitor
C2____________100nF   63V Polyester Capacitor
C3____________470µF   35V Electrolytic Capacitor
C4____________220nF   63V Polyester Capacitor (Optional, see Notes)
C5_____________47µF   25V Electrolytic Capacitor (Optional, see Notes)
C6______________1µF   63V Polyester Capacitor
C7,C8,C9,C10___47µF   25V Electrolytic Capacitors
C11____________47pF   63V Ceramic Capacitor
C12__________1000µF   35V Electrolytic Capacitor
C13__________2200µF   35V Electrolytic Capacitor 

D1_____________5mm. Red LED
D2,D3________1N4004  400V 1A Diodes 

Q1,Q2________2N3819   General-purpose N-Channel FETs
Q3____________BC182   50V 200mA NPN Transistor
Q4____________BD135   45V 1.5A NPN Transistor (See Notes)
Q5____________BDX53A  60V 8A NPN Darlington Transistor
Q6____________BDX54A  60V 8A PNP Darlington Transistor 

J1,J2________6.3mm. Mono Jack sockets
SW1____________1 pole 3 ways rotary switch (Optional, see Notes)
SW2____________SPST Mains switch
F1_____________1.6A Fuse with socket 

T1_____________220V Primary, 48V Center-tapped Secondary
 20 to 30VA Mains transformer
PL1____________Male Mains plug

SPKR___________One or more speakers wired in series or in parallel
 Total resulting impedance: 8 or 4 Ohm
 Minimum power handling: 20W

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Circuit description:

The aim of this design was to reproduce a Combo amplifier of the type very common in the 'sixties and the 'seventies of the past century. It is well suited as a guitar amplifier but it will do a good job with any kind of electronic musical instrument or microphone.

5W power output was a common feature of these widespread devices due to the general adoption of a class A single-tube output stage (see the Vox AC-4 model).

Furthermore, nowadays we can do without the old-fashioned Vib-Trem feature frequently included in those designs.

The present circuit can deliver 10W of output power when driving an 8 Ohm load, or about 18W @ 4 Ohm.

It also features a two-FET preamplifier, two inputs with different sensitivity, a treble-cut control and an optional switch allowing overdrive or powerful treble-enhancement.

Technical data are quite impressive for so simple a design:

Sensitivity: 30mV input for 10W output
Frequency response: 40 to 20KHz -1dB
Total harmonic distortion @ 1KHz and 10KHz, 8 Ohm load: below 0.05% @ 1W, 0.08% @ 3.5W, 0.15% at the onset of clipping (about 10W).

Notes:

• SW1 and related capacitors C4 & C5 are optional.
• When SW1 slider is connected to C5 the overdrive feature is enabled.
• When SW1 slider is connected to C4 the treble-enhancer is enabled.
• C4 value can be varied from 100nF to 470nF to suit your treble-enhancement preferences.
• In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q4) should be in as close thermal contact with the output transistors as possible. Therefore a TO126-case transistor type was chosen for easy bolting on the heatsink, very close to the output pair.
• To set quiescent current, remove temporarily the Fuse F1 and insert the probes of an Avo-meter in the two leads of the fuse holder.
• Set the volume control to the minimum and Trimmer R9 to its minimum resistance.
• Power-on the circuit and adjust R9 to read a current drawing of about 25 to 30mA.
• Wait about 15 minutes, watch if the current is varying and readjust if necessary.

Mini Portable Guitar Amplifier

Mini Portable Guitar Amplifier

Circuit diagram:
Parts:

R1______________22K  1/4W Resistor
C1______________10µF  25V Electrolytic Capacitor
C2_____________100nF  63V Polyester or Ceramic Capacitor
C3_____________220µF  25V Electrolytic Capacitor
IC1__________TDA7052  Audio power amplifier IC
J1,J2__________6.3mm  Stereo Jack sockets (switched)
SPKR___________8 Ohm  Loudspeaker (See Notes)
B1________________9V  PP3 Battery or

3V  Battery (2 x 1.5V AA, AAA Cells in series etc.) 

Clip for PP3 Battery or socket for 2 x 1.5V AA or AAA Cells

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Comments:

This small amplifier was intended to be used in conjunction with an electric guitar to do some low power monitoring, mainly for practice, either via an incorporated small loudspeaker or headphones.

The complete circuit, loudspeaker, batteries, input and output jacks can be encased in a small box having the dimensions of a packet of cigarettes, or it could be fitted also into a real packet of cigarettes like some ready-made units available on the market.

This design can be used in three different ways:

• Loudspeaker amplifier: when powered by a 9V alkaline battery it can deliver about 1.5W peak output power to the incorporated loudspeaker.
• Headphone amplifier or low power loudspeaker amplifier: when powered by a 3V battery (2x1.5V cells) it can drive any headphone set type at a satisfactory output power level or deliver to the incorporated loudspeaker about 60mW of output power. This configuration is useful for saving battery costs.
• Fuzz-box: when powered by a 3V battery (2x1.5V cells) and having its output connected to a guitar amplifier input the circuit will behave as a good Fuzz-box, showing an output square wave with marked rounded corners, typical of valve-circuits output when driven into saturation.

Notes:

• For the sake of simplicity and compactness, this unit employs a dual bridge IC amplifier and a few other parts. For the same reason no volume or tone controls are provided as it is supposed that the controls already existing on the electric guitar will serve satisfactorily to the purpose.
• No power switch is used: the battery voltage will be applied to the circuit when the input plug will be inserted in the input jack socket J1. For this purpose be sure that the input plug is a common 1/4 inch guitar mono jack plug and J1 is a 1/4 inch stereo jack socket.
• The output jack socket J2 must be a switched stereo type. The changeover switching is arranged in such a way that, when a common headphones stereo jack plug is inserted into the socket, the loudspeaker will be disabled and the mono output signal will drive both the headsets in series, allowing full headphone reproduction. When used as a Fuzz-box output, a mono jack plug must be inserted into J2.
• If the amplifier is intended to be encased in a packet of cigarettes, standard loudspeaker diameter should be 57 or 50mm.

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Technical data:

Max output power: 1.5W @ 9V supply - 8 Ohm load; 60mW @ 3V supply - 8 Ohm load
Frequency response: Flat from 20Hz to 20kHz
Total harmonic distortion @ 100mW output: 0.2%
Max input voltage @ 3V supply: 8mV RMS
Minimum input voltage for Fuzz-box operation: 18mV RMS @ 3V supply
Current consumption @ 400mW and 9V supply: 200mA
Current consumption @ 250mW and 9V supply: 150mA
Current consumption @ 60mW and 3V supply: 80mA
Quiescent current consumption: 6mA @ 9V, 4mA @ 3V supply
Fuzz-box current consumption: 3mA @ 3V supply