Positive(+) to Negative(-) Voltage Inverter

This simpe circuit will convert the positive input voltage become negative voltage.

Schematic diagram:

Component list:

Part	Total Qty.	Description
R1	1	24K 1/4 Watt Resistor
R2	1	56K 1/4 Watt Resistor
C1	1	3300pF 25V Ceramic Capacitor
C2	1	47uF 25V Electrolytic Capacitor
C3	1	10uF 25V Electrolytic Capacitor
D1, D2	2	1N4148 Silicon Diode
U1	1	555 Timer
MISC	1	Wire, Board

Notes:

1. V+ can be anywhere from 4 to 16V. -V is one volt less than V+. So for -12V output, use +13V input. The maximum current output of the circuit is about 280mA, more than enough for a few op amps.
2. For better regulation, a 79LOxx series regulator can be used.
3. A zener diode may also be used to regulate the output voltage.

3-30 V/2.5 A Adjustable Stabilized Power Supply

This is Simple 3-30 volt adjustable and stabilized power supply circuit. You can use this circuit for general purpose.

Here the schematic diagram:

Component list:

R1 = 560R 1/4W	C1 = 100nF
R2 = 1,2 K 1/4W	C2 = 2200uF 35-40V
R3 = 3,9 K 1/4W	C3 = 100 pF
R4 = 15K 1/4W	C4 = 100uF/ 35V
R5 = 0,15R 5W
D = B40 C3300/2200, 3A rectifier bridge
P1 = 10K potesiometer	TR1 = BD 135
IC = LM723	TR2 = 2N3055

PCB layout:

Components placement:

For complete explanation, circuit's works and how to build this circuit into the box, download the full tutorial here

Universal Pre-Amplifier

Here the universal pre-amplifier schematic diagram for common input device:

Download the schematic in PDF format

2 Way Cross-Over 3500 Hz (bass and treble)

This is 2 way cross-over for your speaker system. This circuit will handle 2 speaker that are woofer (low frequency) an tweeter (high frequency).

The result will shown as below picture:

Here the schematic diagram of the circuit:

Visit this page for PCB layout and complete explanation about the circuit.