• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Get free circuit help 24/7

New Projects | Privacy Policy | About us | Contact | Disclaimer | Copyright | Videos | Circuits for Beginners | Basic Circuits | Hobby Projects | Transistor Circuits | LED Drivers 

You are here: Home / Power Supply Circuits / Soft-Start Power Supply for Amplifier Loudspeakers

Soft-Start Power Supply for Amplifier Loudspeakers

Last Updated on May 5, 2022 by Swagatam 9 Comments

caution electricity can be dangerous

The proposed slow-start power supply circuit is specially designed for power amplifiers to ensure that the loudspeaker connected with the amplifier do not generate the loud and unwanted "thump" sound during power switch ON.

This also implies that the power supply will safeguard or protect the loudspeaker from the sudden inrush current transient from the power supply, and ensure long life for the loudspeakers.

With this power supply, the connected amplifier and its loudspeaker could be operated safely without the need of other form of protections, such as fuses, delay ON circuits etc.

Power Switch-ON Transient

Most of the amplifier designs, whether DIY or commercial built units, are accompanied with the downside of the generation a loud 'thump' sound on every power switch ON occasions. Normally, this is because of too rapid charging of the output filter electrolytic capacitors, which is unable to stop the initial sudden switch ON transient.

If this problem arises in a high-power amplifier circuit, there may be a high possibility of loudspeakers getting shorted anytime and burned.

An alternate idea is to upgrade the unpredictable amplifier with a slow rising voltage power supply circuit which is discussed in this article. It is fundamentally a basic transistorized regulator, enhanced with a slow-start or soft start feature.

How the Circuit Works

The complete circuit diagram of the slow soft start amplifier power supply is shown below:

The crude supply is supplied by rectifier B and smoothing capacitor CO. Zener diode D1 offers the reference voltage, since the output voltage is lower, at around 600 mV. If it is essential, the intended voltage could be built applying a couple of series connected zeners diodes.

The overall zener voltage could be selected in between 28 V and 63 V (approximately). Switch S1 toggles the supply on and off (connected to the mains AC switch). Whenever it is closed or powered ON, the voltage across C1 goes up in around One second upto its working threshold.

The output voltage begins climbing in accordance with the rising voltage across C1 until the level where the zener diode becomes conductive or the firing threshold of the zener.

When S1 is not closed, or is open, the C1 voltage begins dropping down within approximately Five seconds, caused by the leakage through the base current feed for the transistor T1. In case the amplifier exhibits no significant switch-off voltage spikes, so that no specific turn-off procedure is necessary, it may be possible to totally eliminate the switch S1, and connect the S1 points with a wire link..

The unregulated voltage at C1 must not go beyond 80 V. It must be selected to ensure that there is sufficient voltage drop over T3 to deal with regulation specifications.

Way too high a drop would be a waste of power and even an unnecessary involvement of pricey heat sink.

The basic theory is that, with the supply input fully loaded and the inbound mains AC voltage at its minimum (anticipated) range, there should be approximately 2 volts over the series transistors on the troughs in the ripple waveform.

Alternatively, an acceptable rule of thumb, would be to allow for around 10 volts over T3 (without any load), and expect T3 will, under all circumstances require a minimal heat sink (e.g. 2 mm thick shiny aluminum, about 10 cm by 10 cm).

In severe conditions this might be furthermore essential to enhance T2 with a cooling fins or extensions.

The value of 1000 µF capacitor presented for Cv is merely indicated as a representation.

If you would be interested to precisely design the basic transformer/bridge supply also, coupled to a compatible optimum load, that could be easily calculated through the formula Q = CV (keeping in mind that the rectifier produces one hundred ripples every second.

You'll also like:

  • 1.  1A Step-Down Voltage Regulator Circuit – Switched Mode 78XX Alternative
  • 2.  5V, 12V Buck Converter Circuit SMPS 220V
  • 3.  50 Watt Sine Wave UPS Circuit
  • 4.  Laboratory Power Supply Circuit
  • 5.  Higher Variable Output Voltage from IC 7812
  • 6.  Making a Regulated 9V Battery Eliminator Circuit

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

Reader Interactions

Comments

    Have Questions? Please post your comments below for quick replies! Comments should be related to the above artcile Cancel reply

    Your email address will not be published. Required fields are marked *

  1. Len Jeffrey says

    June 9, 2022

    I have been trying to wire up a circuit that uses p-channel and n-channel fets [two of each] that sense instantaneous positive or negative voltage spikes. The fets turn on either a green or red led. Ideally the green led would sense the negative spike and the red led would sense the positive spike. As each led comes on, the other led would be cancelled or blocked from coming on. Plus the lit led would be delayed going off, maybe 3 seconds. I have been working with 2sk170 and 2n5462 transistors which I have at hand. I can supply the circuit that I have drawn out. Thank you for any help that you can give me.

    mosfet high low pulse detector circuit

    Reply
    • Swagatam says

      June 9, 2022

      The circuit looks OK to me except the two diodes which are placed across the 220K resistor at the gate of the bottom left p channel mosfet. These diodes must be connected between the positive line and the 220k resistor ends.

      Reply
  2. Loraine Mudlong says

    June 6, 2022

    Hello, I have power amplifier equiped in an active loudspeaker, if you turn on the soft start act very fast causing thump sound in the driver.. what would be the problem. Please help me

    Reply
    • Swagatam says

      June 6, 2022

      Hi, did you build the circuit which is shown in the above article?

      Reply
  3. Evans says

    September 17, 2020

    Hello sir,I like the idea, please sir do you have any for Inverter? I would like to have my Inverter start softly.

    Reply
    • Swagatam says

      September 17, 2020

      Evans, the soft-start facility is already included in SG3525 IC, so you can use it for the purpose

      Reply
      • Evans says

        September 17, 2020

        But sir,what of cd4047????

        Reply
        • Swagatam says

          September 17, 2020

          you can try connecting pin9 with ground through a 10k resistor and then add a 10uF capacitor across the positive line and pin9

          Reply
          • Evans says

            September 17, 2020

            Okay sir,let me try

            Reply

Primary Sidebar

Calculators

  • 3-Phase Power (15)
  • 324 IC Circuits (19)
  • 4017 IC Circuits (52)
  • 4060 IC Circuits (25)
  • 555 IC Circuits (98)
  • 741 IC Circuits (19)
  • Arduino Engineering Projects (83)
  • Audio and Amplifier Projects (114)
  • Battery Chargers (82)
  • Car and Motorcycle (94)
  • Datasheets (46)
  • Decorative Lighting (Diwali, Christmas) (33)
  • Electronic Components (100)
  • Electronic Devices and Circuit Theory (36)
  • Electronics Tutorial (116)
  • Fish Aquarium (5)
  • Free Energy (34)
  • Fun Projects (13)
  • GSM Projects (9)
  • Health Related (20)
  • Heater Controllers (29)
  • Home Electrical Circuits (102)
  • How to Articles (20)
  • Incubator Related (6)
  • Industrial Electronics (28)
  • Infrared (IR) (40)
  • Inverter Circuits (98)
  • Laser Projects (12)
  • LED and Light Effect (93)
  • LM317/LM338 (21)
  • LM3915 IC (25)
  • Meters and Testers (65)
  • Mini Projects (148)
  • Motor Controller (67)
  • MPPT (7)
  • Oscillator Circuits (26)
  • PIR (Passive Infrared) (8)
  • Power Electronics (34)
  • Power Supply Circuits (77)
  • Radio Circuits (10)
  • Remote Control (48)
  • Security and Alarm (61)
  • Sensors and Detectors (120)
  • SG3525 IC (5)
  • Simple Circuits (75)
  • SMPS (29)
  • Solar Controllers (60)
  • Timer and Delay Relay (53)
  • TL494 IC (5)
  • Transformerless Power Supply (8)
  • Transmitter Circuits (40)
  • Ultrasonic Projects (16)
  • Water Level Controller (45)

Calculators

  • AWG to Millimeter Converter
  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Small Signal Transistor(BJT) and Diode Quick Datasheet
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator

© 2023 · Swagatam Innovations