60w bass amplifier circuit diagram explanation

Output power: 40W into 8 ohms, 60W into 4 ohms

Amplifier circuit schematic:

Amplifier Section:

1W resistor R1 6K8

R2, R4 470R 1/4W resistor

R3 2K 1/2W Metal Ceramic Trimmer

R5, R6 4K7 1/2W resistor

R7 220R 1/2W resistor

1/2W resistor R8 2K2

R9 50K 1/2W Metal Ceramic Trimmer

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

C71000μF50V electrolytic capacitor

C8 63V2200μF electrolytic capacitor (see notes)

D1 LED any type and color

D2 diode bridge 200V 6A

Q1, Q2 BD139 80V 1.5A NPN transistor

3rd MJ11016 120V 30A NPN Darlington transistor (see notes)

Q4 MJ11015 120V 30A PNP Darlington transistor (see notes)

SW1 Single Pole Single Throw (SPST) Power Switch

F1 4A fuse socket

48-50V Secondary 75 to 150VA Power Transformer T1 Primary 220V

PL1 power plug

SPKR wiring one or more speakers in series or parallel. Total impedance: 8 or 4 ohms. Minimum power handling: 75W

Preamplifier circuit schematic:

Preamplifier Section:

P1 10K linear potentiometer

P2 10K resistor. Potentiometer

R1, R2 68K 1/4W resistor

1/4W resistor R3 680K

1/4W resistor R4 220K

R5 33K 1/4W resistor

1/4W resistor R6 2K2

1/4W resistor R7 5K6

R8, R18 330R 1/4W resistor

R9 47K 1/4W resistor

R10 18K 1/4W resistor

R11 4K7 1/4W resistor

R12 1K 1/4W resistor

1/4W resistor R13 1K5

R14, R15, R16 100K 1/4W resistor

R17 10K 1/4W resistor

C1, C4, C8, C9, C10 10μF 63V electrolytic capacitors

C247μF63V electrolytic capacitor

C3 47PF 63V ceramic capacitor

C5 220nF capacitor 63V polyester

5233 470NF 63V Polyester Capacitor

C7 100nF 63V polyester capacitor

C112 20μF 63V electrolytic capacitor

Q1, Q3 BC546 NPN transistor 65V 100mA

Q2 BC556 65V 100mA PNP transistor

J1, J2 6.3 mm. mono jack,

SPST switch SW1

Circuit Description:

The design uses a complete power amplifier circuit, using a single power supply of about 60V, OTL circuit structure, and the output level is coupled to the speaker via capacitors. The preamplifier is powered by the same 60V single power supply as the power amplifier.

Technical data:

Sensitivity:

40W output into 8 ohms, 70mV input

60W output into 4 ohms, 63mV input

Frequency response:

50Hz to 20KHZ - 0.5dB; 1.5dB @ 40Hz - 3.5dB @ 30Hz

Total Harmonic Distortion @ 1KHz and 8 Ohm load:

Less than 0.1% up to 10W; 0.2% @ 30W

Total Harmonic Distortion at 10KHz and 8 ohm load:

Less than 0.15% up to 10W; 0.3% @ 30W

Total Harmonic Distortion @ 1KHz and 4 Ohm load:

Less than 0.18% up to 10W; 0.4% @ 60W

Total Harmonic Distortion at 10KHz and 4 ohm load:

Less than 0.3% up to 10W; 0.6% @ 60W

Bass Control:

Fully clockwise = 13.7 dB @ 100 Hz; 23 dB @ 10 kHz

Center position = 4.5 dB @ 100 Hz

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 recommended minimum. A 3300μF capacitor or two 2200μF capacitors wired in parallel would be a better choice.

Such a design may be too large for the Darlington transistor types listed on the market. You can also replace them with MJ11014 (Q3) and MJ11013 (Q4) or TIP142 (Q3) and TIP147 (Q4).

The T1 transformer can also be a 24+24 or 25+25V type (i.e. a 48V or 50V center tap). Obviously, the center tap must be left floating.

SW1 switch inserts the low-cut function on.

In all cases where a Darlington transistor is used as an output device, it is essential that the sensing transistor (Q2) should be in as close thermal contact as possible with the output transistor. Therefore, a TO126 case transistor type is chosen to easily bolt the heat sink, very close to the output pair.

R9 must be trimmed from the positive lead of C7 and ground so as to measure about half the supply voltage. A better setup can be achieved by using an oscilloscope at maximum output power to obtain a symmetrical output waveform without clipping.

To set the quiescent current, temporarily remove fuse F1 and insert the AVO meter's long probes into the two wires of the fuse holder.

Set the volume control to minimum and trim R3 to its minimum resistance.

Power on the circuit and adjust R3 to read the current graph for a current of approximately 30-35mA.

Wait about 15 minutes and watch if the current changes and adjust if necessary.