500 Circuits: 2011

A1 is a single or dual opamp for audio: OPA134, 2134, NE5532, 5534.

It is a very useful thing , to have a small headphone amplifier , capable of driving a couple of pairs phones. Fortunately, the headphone amp has a much easier job to do, in that neither the output power requirements nor the load characteristics are so severe, since headphones typically have a load, impedance , higher of 50 ohm, (typical 600 ohm), and only require 1-2V RMS. max, for normal output. Since only a low power output is required, a Class A stage, is perfectly feasible. For adequate Class A operation the output transistors Q5-6, should pass say 100mA each. With ?15V supply this would mean 1.5Watts dissipation, so a smallish Heatsink, will be needed for each. With RV1 adjust input audio signal and Tr1 adjust the output DC Offset voltage for 0V (?30mV). For stereo application , you need two unit, of this amp. by L. Hood

R1-4= 1.2Kohm R12= 4.7 ohm C8-10= 470uF 25V
R2-3= 3.9Kohm RV1= 10Kohm Log. pot. C9-11= 100nF 100V ceramic
R5-10= 10Kohm TR1= 10Kohm Trimmer Q1-3= BC184
R6=100Kohm C1= 4.7uF 63V MKT Q2-4= BC214
R7-9= 2.2Kohm C2-7= 100uF 25V Q5= BD136 or BD538
R8= 150 ohm C3-5= 100nF 100V MKT Q6= BD135 or BD537
R11-13= 6R8 ohm C4-6= 100uF 16V All resistors is 1/4W 1%

R1=470K 0,5W
R13-21=820K 0.5W
C8-9=0.1uF 630V
R2-5= 2K2 0.5W
R14-22=5K6 0.5W
C10-14=0.47uF 630V
R3=150K 0.5W
R15-20= 680K 0.5W
C11-13=25uF 40V
R4= 220K 0.5W
R16-19=100K 0.5W
V1=E80CC
R6-10= 56K 0.5W
R17-18=3K3 1W
V2=E80CC
R7=3.9K 0.5W
R24=470R 2W
V3-4=EL34
R8= 220R 0.5W
TR1-2=470R 1W Variable (adj. 270?)
Rectifier tube= Z2C
R9= 1M 0.5W
C1-3-6-7=0.1uf 630V
T1=Audio Transformer for 2x EL34 Push Pull
R11= 39K 1W
C2=220pF 600v
R12-23= 180K 0.5W
C4-5=16uF 550V

Here is a little audio amplifier similar to what you might find in a small transistor radio. The input stage is biased so that the supply voltage is divided equally across the two complimentary output transistors which are slightly biased in conduction by the diodes between the bases. A 3.3 ohm resistor is used in series with the emitters of the output transistors to stabilize the bias current so it doesn't change much with temperature or with different transistors and diodes. As the bias current increases, the voltage between the emitter and base decreases, thus reducing the conduction. Input impedance is about 500 ohms and voltage gain is about 5 with an 8 ohm speaker attached. The voltage swing on the speaker is about 2 volts without distorting and power output is in the 50 milliwatt range. A higher supply voltage and the addition of heat sinks to the output transistors would provide more power. Circuit draws about 30 milliamps from a 9 volt supply.

R1= 22Kohm
C1-7-9= 100nF 1KV
V1= ECC81
R2-3= 1Kohm
C2= 220uF 350V
V2= 6BX7
R4-5= 1.5Kohm
C3= 150nF 400V
T1= 220V@2X250V/6.3V/6.3V
R6-7= 470Kohm
C4= 100uF 25V
T2=Audio transformer
R8-9= 1Kohm 2W
C6-8= 2X100?F 350V
RV1= 250Kohm Log. pot.
D1-2= 1N4007

R1=1Kohm
C2-6=100uF 25V
C6=100uF 25V
R2-3=12Kohm
C3=100nF 100V
IC1=LM359N
R4-5-6=10Kohm
C4=1pF ceramic
J1-2=BNC connector
C1=10nF 100V
C5=10nF 100V

Frequency 30 MHz
C1 150 pf
C2 15 pf
C3 39 pf
L1 1.5 uH
L2 1.2 uH
RFC 33 uH
Q1 2N5109

วันศุกร์ที่ 28 มกราคม พ.ศ. 2554