Ultra-low quiescent current AF power amplifier

Power Amplifier 300W

POWER OUTPUT:

• 200W rms/8 ohm 
• 310W rms/4 ohm
• 800W rms/8 ohm (Bridge mode)

FREQUENCE RESPONSE 

• 20HZ-20KHZ +/-0.5dB 

INPUT SENSITIVITY 

• 1V for 200W/300W 

HUM AND NOISE

•  -105dB 

THD 

• <0.1% 

DAMPING FACTOR

•  65

Part list:

R1-19= 1Kohm 5W	R34-35= 0.1ohm 5W	C14-17= 100uF 100V
R2-3= 4.7Kohm	R36-43= 39ohm	C15= 100nF 250V polyester
R4-5= 22ohm	R37-42= 5.6Kohm 1W	Q1-2-3= BC547
R6-14= 10Kohm	R38-41= 220ohm 5W	Q4-5-6= BC557
R7-8= 1Kohm	R39-40= 0.1ohm 5W	Q7-11-12= BD140 or BC640
R9-23*=10K ohm	R44-45= 0.1ohm 5W	Q8= BC549
R10= 10ohm *see circuit sch.	R46= 4.7ohm 2W	Q9-10-15= BD139 or BC639
R11-13= 2.2Kohm	R47= 100ohm	Q13-14= MJ15004
R12= 22Kohm	C1= 2.2uF 25V	Q16-17= MJ15003
R15-16= 22ohm	C2-6= 330pF ceramic	TR1= 2K2 Trimmer
R17-18=  4.7Kohm	C3-8= 100uF 100V	F1-2= 5A Fuse Fast
R20-25= 390ohm	C4-9= 100nF 250V	D1-3= 5.1V 0.5W Zener
R21= 6.8Kohm	C5= 100nF 100V polyester	D2= 62V/5W Zener or 47v and 15V in series
R22=  4.7Kohm	C7= 100uF 25V	D4-5= 1N4004
R24-26-33= 220ohm	C10= 1.5nF 100V polyester	L1=10 turns diameter 1mm in 15mm diameter tube
R27-32= 100ohm 1W	C11-12= 1.5nF 100V polyester
R28,29,30,31= 100ohm	C13-16= 100nF 250V polyester	*Use R23=6k8 for 4 ohm loudspeakers

Audio amplifier 16 W

All resistors are 5 or 10 percent tolerance, 1/4-watt all capacitors are 10 percent tolerance, rated 35 volts or higher this circuit provides 16 watts of amplification. it is built using two LM383 power audio.

U1 U2	LM383 8 watt audio amplifier ic
R1, R3	220 ohm resistor
R2, R4	2.2 ohm resistor
R5	1 megohm resistor
R6	100k audio taper potentiometer
C1, C7	10uf electrolytic capacitor
C2, C5	470uf electrolytic capacitor
C3, C4, C6	0.2uf ceramic capacitor
SPKR1	4 to 8 ohm speaker (up to 8 inches diameter)

4 watt audio amplifier circuit

I have recently included a page about AF amplifers for use with Homebrew rigs. In this I mentioned that I may include a practical one-watt circuit, complete with PCB foil and layout. Here it is, but I have taken the liberty of engineering it to provide 4-watts of AF output and with a frequency response almost suitable for Hi-Fi applications.

The circuit is very simple and incorporates darlington output transistors that will provide more than enough output current than is needed to drive a 3-ohm speaker. The gain may be pre-set for a variety of input levels, making it suitable for amplifying computer and cassette-deck Line-output levels. The input level is also suitable for use with the TDA7000 receiver. All components are easily available and I will shortly be making this project available as a kit. Naturally, the project will be built on a PCB which will also be available separately. Here is the first PCB, assembled and working.

The completed unit is 60mm x 75mm and only 30mm deep. The depth could be reduced to 10mm if the output capacitor is mounted at the speaker and the on-board electrolytics are mounted horisontally. Here are the typical performance figures that may be expected from the finished amplifer using a 3-ohm load with a 13.8-volt supply. I see no reason why the supply voltage cannot be increased a little to obtain more output power:

Parameter	Minimum	Maximum	Units
Supply voltage	8	15	volts
Output power	-	5.4	Watts
I/P for full O/P	30	4000	mV (RMS)
Noise O/P no I/P	-	0.0005	Volts RMS
Supply current (no-signal)	-	50	mA
Supply Current (Full O/P)	-	1.9	Amperes
3dB Frequency Response	42	34000	Hertz
6dB Frequency Response	21	62000	Hertz
Distortion at 2-watts	-	0.01	% (Vgain=10)

No heatsinking is required for the output transistors when running at a modest output level with either speech or music. A small heatsink should be fitted to the two TIP41 transistors if running a constant tone level. The heatsink could be bolted directly to the TIP41s without electrical isolation if the heatsinks are not going to touch anything. A heatsink with a 15-square surface area is all that is required. Here is the circuit of the amplifer.

The gain of the amplifer is set by selecting the value of the feedback resistor (Rf) on the PCB. The value of Rf is equal to 4700 / (Vgain -1) where Vgain is the voltage gain required. 4-volts RMS is the full-output level. Here is a guide for selecting the resistor.


ValueVgainTypical use
2K2 3 1300mV RMS - High levels (Small radio speaker)
470R 11 400mV RMS - e.g. computer/tape-deck Line-out
100R 48 80mV RMS - e.g. from TDA7000 RX
33R 143 30mV RMS (e.g. from microphones)


The distortion and noise levels may increase at higher gain levels, but the test board was measured with Vgain = 10 and was driving a 3-ohm car Hi-Fi speaker. With higher-impedance speakers the frequency response will become wider but the output power will reduce a little. There was no trace of instability throughout the AF range and up to 150KHz so I thought it unncecssary to include a Zobel network. Incidentally, four-watts of AF will have the wife banging on the workshop walls, so do not underestimate QRP AF!

Subwoofer Amplifier

The fins were added to a simple flat aluminium panel, and are made from 20 x 20 x 3mm aluminium angle. Their purpose is threefold - they improve the performance of the plate as a heatsink (although this is not necessary with the BP4078 PWM amp), they make the panel a lot more rigid, and provide essential protection for the volume control and phase switch. It also looks better IMO - it looks like it means business, rather than looking like one of those wimpy 50W plate amps you see advertised.

Complite, original article sourse and right reserverd here

Power amplifier 65W with HEXFET

A medium power amplifier that is characterized by a lot of good sound quality, but simultaneously is very simple in the construction. full article here

Telephone Headphone Amplifier

Compact, inexpensive and low component count telecom head- set can be constructed using two readily available transistors and a few other electronic components. This circuit is very useful for hands-free operation of EPABX and pager communication. Since the circuit draws very little current, it is ideal for parallel operation with electronic telephone set. Working of the circuit is simple and straightforward. Resistor R1 and an ordinary neon glow- lamp forms a complete visual ringer circuit. This simple arrangement does not require a DC blocking capacitor because, under idle conditions, the telephone line voltage is insufficient to ionise the neon gas and thus the lamp does not light. Only when the ring signal is being received, it flashes at the ringing rate to indicate an incoming call. The bridge rectifier using diodes D1 through D4 acts as a polarity guard which protects the electronic circuit from any changes in the telephone line polarity. Zener diode D5 at the output of this bridge rectifier is used for additional circuit protection. Section comprising transistor T1, resistors R2, R3 and zener diode D6 forms a constant voltage regulator that provides a low voltage output of about 5 volts. Dial tone and speech signals from exchange are coupled to the receiving sound amplifier stage built around transistors T2 and related parts, i.e. resistors R7, R6 and capacitor C5. Amplified signals from collector of transistor T2 are connected to dynamic receiver RT-200 (used as earpiece) via capacitor C7. A condenser microphone, connected as shown in the circuit, is used as transmitter. Audio signals developed across the microphone are coupled to the base of transistor T1 via capacitor C3. Resistor R4 determines the DC bias required for the microphone. After amplification by transistor T1, the audio signals are coupled to the telephone lines via the diode bridge. The whole circuit can be wired on a very small PCB and housed in a medium size headphone, as shown in the illustration. For better results at low line currents, value of resistor R2 may be reduced after testing