Mini-MosFet Audio Amplifier

Mini-MosFet Audio Amplifier

Power Amplifier Circuit diagram:Power Amplifier Parts:

R1_______________2K2 1/4W Resistor
R2______________27K  1/4W Resistor
R3,R4____________2K2 1/2W Trimmers Cermet or Carbon (or 2K)
R5_____________100R  1/4W Resistor
R6_______________1K  1/4W Resistor
R7,R8__________330R  1/4W Resistors 

C1______________22µF  25V Electrolytic Capacitor
C2______________47pF  63V Polystyrene or Ceramic Capacitor
C3,C4__________100µF  50V Electrolytic Capacitors
C5____________2200µF  50V Electrolytic Capacitor 

Q1____________BC550C  45V 100mA Low noise High gain NPN Transistor
Q2___________IRF530  100V 14A N-Channel Hexfet Transistor (or MTP12N10)
Q3__________IRF9530  100V 12A P-Channel Hexfet Transistor (or MTP12P10)

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Comments:

This project was a sort of challenge: designing an audio amplifier capable of delivering a decent output power with a minimum parts count, without sacrificing quality.

The Power Amplifier section employs only three transistors and a handful of resistors and capacitors in a shunt feedback configuration but can deliver more than 18W into 8 Ohm with <0.08%>

Setting up the Power Amplifier:

The setup of this amplifier must be done carefully and with no haste:

1. Connect the Power Supply Unit (previously tested separately) to the Power Amplifier but not the Preamp: the input of the Power Amplifier must be left open.
2. Rotate the cursor of R4 fully towards Q1 Collector.
3. Set the cursor of R3 to about the middle of its travel.
4. Connect a suitable loudspeaker or a 8 Ohm 20W resistor to the amplifier output.
5. Connect a Multimeter, set to measure about 50V fsd, across the positive end of C5 and the negative ground.
6. Switch on the supply and rotate R3 very slowly in order to read about 23V on the Multimeter display.
7. Switch off the supply, disconnect the Multimeter and reconnect it, set to measure at least 1Amp fsd, in series to the positive supply (the possible use of a second Multimeter in this place will be very welcomed).
8. Switch on the supply and rotate R4 very slowly until a reading of about 120mA is displayed.
9. Check again the voltage at the positive end of C5 and readjust R3 if necessary.
10. If R3 was readjusted, R4 will surely require some readjustment.
11. Wait about 15 minutes, watch if the current is varying and readjust if necessary.
12. Please note that R3 and R4 are very sensitive: very small movements will cause rather high voltage or current variations, so be careful.
13. Those lucky enough to reach an oscilloscope and a 1KHz sine wave generator, can drive the amplifier to the maximum output power and adjust R3 in order to obtain a symmetrical clipping of the sine wave displayed.

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Preamp Circuit diagram:

Preamp Parts:

P1______________50K  Log. Potentiometer (or 47K)
 (twin concentric-spindle dual gang for stereo)
P2,P3__________100K  Linear Potentiometers
 (twin concentric-spindle dual gang for stereo) 

R1_____________220K  1/4W Resistor
R2_____________100K  1/4W Resistor
R3_______________2K7 1/4W Resistor
R4,R5____________8K2 1/4W Resistors
R6_______________4K7 1/4W Resistor
R7,R8,R13________2K2 1/4W Resistors
R9_______________2M2 1/4W Resistor
R10,R11_________47K  1/4W Resistor
R12_____________33K  1/4W Resistor
R14____________470R  1/4W Resistor
R15_____________10K  1/4W Resistor
R16______________3K3 1/4W Resistor (See Notes) 

C1,C2,C9_______470nF  63V Polyester Capacitors
C3,C4___________47nF  63V Polyester Capacitors
C5,C6____________6n8  63V Polyester Capacitors
C7______________10µF  63V Electrolytic Capacitor
C8,C10__________22µF  25V Electrolytic Capacitors
C11____________470µF  25V Electrolytic Capacitor (See Notes) 

Q1,Q3_________BC550C  45V 100mA Low noise High gain NPN Transistors
Q2___________2N3819   General-purpose N-Channel FET

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Comments:

The Preamp sensitivity and overload margin were designed to cope with most modern music programme sources like CD players, Tape recorders, iPods, Computer audio outputs, Tuners etc. The source selecting switches and input connectors are not shown and their number and arrangement are left to the constructor's choice.

To obtain a very high input overload margin, the volume control was placed at the preamp input. After a unity gain, impedance converter stage (Q1) a negative-feedback Baxandall-type Bass and Treble tone control stage was added. As this stage must provide some gain (about 5.6 times) a very low noise, "bootstrapped" two-transistors circuitry with FET-input was implemented. This stage features also excellent THD figures up to 4V RMS output and a low output impedance, necessary to drive properly the Mini-MosFet Power Amplifier, but can also be used for other purposes.

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Regulated Power Supply Circuit diagram:

Regulated Power Supply Parts:

R1_______________3R9 1 or 2W Resistor
R2______________22R  1/4W Resistor
R3_______________6K8 1/4W Resistor
R4_____________220R  1/4W Resistor
R5_______________4K7 1/2W Resistor

C1____________3300µF  50V Electrolytic Capacitor (or 4700µF 50V)
C2,C5__________100nF  63V Polyester Capacitors
C3______________10µF  63V Electrolytic Capacitor
C4_____________220µF  50V Electrolytic Capacitor 

D1_____Diode bridge  100V 4A
D2___________1N4002  200V 1A Diode
D3______________LED  Any type and color 

IC1___________LM317T 3-Terminal Adjustable Regulator
Q1____________TIP42A  60V 6A PNP Transistor
SW2_____________SPST  Mains switch
T1_____________230V Primary, 35-36V (Center-tapped) Secondary,
 50-75VA Mains transformer (See Notes) 

PL1____________Male Mains plug with cord

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Comments:

A very good and powerful Regulated Power Supply section was implemented by simply adding a PNP power transistor to the excellent LM317T adjustable regulator chip. In this way this circuit was able to deliver much more than the power required to drive two Mini-MosFet amplifiers to full output (at least 2Amp @ 40V into 4 Ohm load) without any appreciable effort.

Notes:

• Q2 and Q3 in the Power Amplifier must be mounted each on a finned heatsink of at least 80x40x25mm.
• Q1 and IC1 in the Regulated Power Supply must be mounted on a finned heatsink of at least 45x40x17mm.
• A power Transformer having a secondary winding rated at 35 - 36V and 50VA (i.e. about 1.4Amp) is required if you intend to use Loudspeaker cabinets of 8 Ohm nominal impedance. To drive 4 Ohm loads at high power levels, a 70 - 75VA Transformer (2Amp at least) will be a better choice. These transformers are usually center tapped: the central lead will be obviously left open.
• For the stereo version of this project, R16 and C11 in the Preamp will be in common to both channels: therefore, only one item each is necessary. In this case, R11 must be a 1K5 1/2W resistor. The value of C11 will remain unchanged.

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Technical data:

Output power:

18 Watt RMS into 8 Ohm (1KHz sine wave) - 30 Watt RMS into 4 Ohm
Input sensitivity of the complete Amplifier:
160mV RMS for full output
Power Amplifier Input sensitivity:
900mV RMS for full output
Power Amplifier Frequency response @ 1W RMS:
flat from 40Hz to 20KHz, -0.7dB @ 30Hz, -1.7dB @ 20Hz
Power Amplifier Total harmonic distortion @ 1KHz:
100mW 0.04% 1W 0.04% 10W 0.06% 18W 0.08%
Power Amplifier Total harmonic distortion @10KHz:
100mW 0.02% 1W 0.02% 10W 0.05% 18W 0.12%
Unconditionally stable on capacitive loads
Preamp Maximum output voltage:4V RMS
Preamp Frequency response:flat from 20Hz to 20KHz
Preamp Total harmonic distortion @ 1KHz:
1V RMS 0.007% 3V RMS 0.035%
Preamp Total harmonic distortion @10KHz:
1V RMS 0.007% 3V RMS 0.02%
Bass control frequency range referred to 1KHz:
±20dB @ 40Hz
Treble control frequency range referred to 1KHz:
+18dB/-20dB @ 20KHz

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.

60W Bass Amplifier

60W Bass Amplifier

Amplifier circuit diagram:
Amplifier parts:

R1__________________6K8    1W Resistor
R2,R4_____________470R   1/4W Resistors
R3__________________2K   1/2W Trimmer Cermet
R5,R6_______________4K7  1/2W Resistors
R7________________220R   1/2W Resistor
R8__________________2K2  1/2W Resistor
R9_________________50K   1/2W Trimmer Cermet
R10________________68K   1/4W Resistor
R11,R12______________R47   4W Wirewound Resistors

C1,C2,C4,C5________47µF   63V Electrolytic Capacitors
C3________________100µF   25V Electrolytic Capacitor
C6_________________33pF   63V Ceramic Capacitor
C7_______________1000µF   50V Electrolytic Capacitor
C8_______________2200µF   63V Electrolytic Capacitor (See Notes) 

D1_________________LED    Any type and color
D2________Diode bridge   200V 6A  

Q1,Q2____________BD139    80V 1.5A NPN Transistors
Q3_____________MJ11016   120V 30A NPN Darlington Transistor (See Notes)
Q4_____________MJ11015   120V 30A PNP Darlington Transistor (See Notes) 

SW1_______________SPST Mains switch
F1__________________4A Fuse with socket 

T1________________220V Primary, 48-50V Secondary 75 to 150VA
 Mains transformer (See Notes) 

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: 75W

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Preamplifier circuit diagram:

Preamplifier parts:

P1_________________10K   Linear Potentiometer
P2_________________10K   Log. Potentiometer
R1,R2______________68K   1/4W Resistors
R3________________680K   1/4W Resistor
R4________________220K   1/4W Resistor
R5_________________33K   1/4W Resistor
R6__________________2K2  1/4W Resistor
R7__________________5K6  1/4W Resistor
R8,R18____________330R   1/4W Resistors
R9_________________47K   1/4W Resistor
R10________________18K   1/4W Resistor
R11_________________4K7  1/4W Resistor
R12_________________1K   1/4W Resistor
R13_________________1K5  1/4W Resistor
R14,R15,R16_______100K   1/4W Resistors
R17________________10K   1/4W Resistor 

C1,C4,C8,C9,C10____10µF   63V Electrolytic Capacitors
C2_________________47µF   63V Electrolytic Capacitor
C3_________________47pF   63V Ceramic Capacitor
C5________________220nF   63V Polyester Capacitor
C6________________470nF   63V Polyester Capacitor
C7________________100nF   63V Polyester Capacitor
C11_______________220µF   63V Electrolytic Capacitor 

Q1,Q3____________BC546    65V 100mA NPN Transistors
Q2_______________BC556    65V 100mA PNP Transistor 

J1,J2___________6.3mm. Mono Jack sockets 

SW1_______________SPST Switch

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Circuit description:

This design adopts a well established circuit topology for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker(s). The advantages for a guitar amplifier are the very simple circuitry, even for comparatively high power outputs, and a certain built-in degree of loudspeaker protection, due to capacitor C8, preventing the voltage supply to be conveyed into loudspeakers in case of output transistors' failure.

The preamp is powered by the same 60V rails as the power amplifier, allowing to implement a two-transistors gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability.

Technical data:

Sensitivity:

70mV input for 40W 8 Ohm output
63mV input for 60W 4 Ohm output

Frequency response:

50Hz to 20KHz -0.5dB; -1.5dB @ 40Hz; -3.5dB @ 30Hz
Total harmonic distortion @ 1KHz and 8 Ohm load:
Below 0.1% up to 10W; 0.2% @ 30W
Total harmonic distortion @ 10KHz and 8 Ohm load:
Below 0.15% up to 10W; 0.3% @ 30W
Total harmonic distortion @ 1KHz and 4 Ohm load:
Below 0.18% up to 10W; 0.4% @ 60W
Total harmonic distortion @ 10KHz and 4 Ohm load:
Below 0.3% up to 10W; 0.6% @ 60W

Bass control:

Fully clockwise = +13.7dB @ 100Hz; -23dB @ 10KHz
Center position = -4.5dB @ 100Hz
Fully counterclockwise = -12.5dB @ 100Hz; +0.7dB @ 1KHz and 10KHz

Low-cut switch:

-1.5dB @ 300Hz; -2.5dB @ 200Hz; -4.4dB @ 100Hz; -10dB @ 50Hz

Notes:

• The value listed for C8 is the minimum suggested value. A 3300µF capacitor or two 2200µF capacitors wired in parallel would be a better choice.
• The Darlington transistor types listed could be too oversized for such a design. You can substitute them with MJ11014 (Q3) and MJ11013 (Q4) or TIP142 (Q3) and TIP147 (Q4).
• T1 transformer can be also a 24 + 24V or 25 + 25V type (i.e. 48V or 50V center tapped). Obviously, the center-tap must be left unconnected.
• SW1 switch inserts the Low-cut feature when open.
• In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q2) 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.
• R9 must be trimmed in order to measure about half the voltage supply across the positive lead of C7 and ground. A better setting can be done using an oscilloscope, in order to obtain a symmetrical clipping of the output wave form at maximum output power.
• 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 R3 to its minimum resistance.
• Power-on the circuit and adjust R3 to read a current drawing of about 30 to 35mA.
• Wait about 15 minutes, watch if the current is varying and readjust if necessary.

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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

IR Remote-Control Checker

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Suitable for any Infra-red emitting device -- 3V battery supply

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Circuit diagram:

Parts:

R1_____________470K  1/4W Resistor
R2______________47R  1/4W Resistor
D1______________LED  (Any dimension, shape and color)
Q1____________Infra-red Photo Transistor (Any cheap type)
Q2____________BC327   45V 800mA PNP Transistor
SW1____________SPST  Toggle or Slide Switch (Optional, see Note)
B1_______________3V Battery (2 x 1.5V AA, AAA or smaller type Cells in series)

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Comments:

A very simple device allowing a quick check of common Infra-red Remote-Controls can be useful to the electronics amateur, frequently asked to repair or test these ubiquitous devices.

A reliable circuit was designed with a handful of components: the LED will flash when any of the Remote-Control pushbuttons will be pressed. The side of the Remote-Control bearing the IR emitting diode(s) must be directed towards the Photo Transistor (Q1) of the checker circuit: maximum distance should not exceed about 20 - 25cm.

Note:

• Current drawing of the circuit is less than 1mA when the LED illuminates and 0mA when no signal is picked-up by the Photo Transistor: therefore, SW1 can be omitted.