In this post we learn how to make a 10 step sequentially switching latch circuit which is used for switching ON 10 high power amplifiers sequentially. The idea was requested by Mr. Jerry B. Williams

Circuit to Switch ON Power Amplifiers in Sequence

My circuit question will be more detailed than you really care to know about, but it is my wish for you to understand my entire application. Hopefully, you will be able to assist me here in my endeavor!!! First…..I am – NOT – a circuit designer!!! I am a – BUILDER – of electronic equipment. You give me a schematic and I can design the PCB – and – the mechanical chassis the PCB will go into.

However, I do not have an understanding about all of the electronic components.

My circuit application — will be used to sequentially power-on the high-power audio power amplifiers used in sound-reinforcement systems for concerts in arenas and stadiums.

The amplifiers are mounted in 19″ racks and when AC-power is applied to the racks, instead of ALL of the amplifiers turning on simultaneously at the same time, I would like for the amplifiers to be turned-on sequentially with a time-delay.

The amplifiers themselves will be controlled by a high-current solid-state relay (i.e. LED). So, here is what I would like to obtain…..

A schematic of a sequential power-on circuit capable of driving 10 LED’s. Upon the circuit being powered-up with its DC voltage, there would be a 3 – 5 second delay for the circuit to stabilize and then the first “ON” pulse would be initiated to turn-on the first LED (which is actually inside the solid-state relay). – ALL – of the LED’s are to remain “ON” until eventually powered “OFF”!!! After a 3-second delay, the second “ON” pulse is initiated and then it also remains “ON”.

After another 3-second delay, the third “ON” pulse is initiated and it also remains “ON” and the sequence continues until all 10 LED’s (solid-state relays) are turned-on and remain “ON” until eventually powered “OFF” after the concert is over and the audio racks are powered down to be loaded into their trucks. As I mentioned earlier, the driven LED’s are actually the LED’s inside of a 25-Amp solid-state relay.

The AC-load side of these solid-state relays will be wired to U.S. standard “wall-outlet plugs” on the rear panel of a rack-mount chassis which will be mounted to the rear of the amplifier racks.

I do understand already that the circuit will need its own DC power-supply and I am planning on designing a PCB for this circuitry and a small AC/DC power-supply module. Should you respond back to me directly with an e-mail, I could respond back to you with a photograph showing some of these audio racks.

Each rack outputs 10,000 Watts of audio power!!! I use either Altium or CADENCE/OrCAD for my schematics and PCB designs. If you are unable to provide me with a circuit schematic designed to fulfill the requirement as I detailed above, then perhaps you can provide me the name of someone who can.

However, as I read through your article above, you do seem to be quite capable in the design of timing circuits. THANKS!!!

One final comment…..this circuit – MUST – be ultra-reliable and – NOT – fail, as any type of “OFF” failure could very easily bring to an end a major concert by a world-famous artist, band and/or musician!!!



Jerry B. Williams

The Design

The requested design for a 10 step sequential latch switch circuit with adjustable delay is presented in the below shown diagram, and can be understood with the help of the following explanation:

The circuit design employed here is basically a standard IC 4017 and IC 555 based chaser, wherein the IC 555 sends the clocks to pin#14 of the IC 4017 enabling its output to generate a sequential chasing output across its pin#3 to

However as per the internal specification of the IC 4017 which is a 10 stage Johnson decade counter, register IC, the sequencing logic highs across its output pinouts shut-off sequentially as the logic jumps from one pinout to the other.

In order to ensure that the sequencing logic get latched across the pinouts, we introduce SCRs for triggering the external load. SCRs as we know have the property of getting latched to DC switching in response to a single trigger to their gates, and we take the advantage of this characteristic of this device for acquiring the latched sequencing outputs from the 4017 pinouts.

Circuit Diagram

As per the request the sequencing must freeze when all the 10 outputs are switched ON, we achieve this by linking pin#11 of the IC with pin#13, which ensures that the IC simply locks down itself as soon as the logic reaches the last pinout in the order: pin#11.

The delay time for the sequencing shifts can be set by adjusting the 100k pot associated with the IC 555.

This circuit fulfills the intended 10 step sequential switching latch circuit which is applied for amplifiers, nevertheless the design being too flexible can be customized for any other similar application need.

Parts List

All SCR gate resistors: 1K, 1/4 watt
All other resistors can also be 1/4 watt rated
All SCRs can be BT169, the mentioned C106 is not appropriate and must be ignored.
The SSR modules can be as per the user presfrence.

Need Help? Please send your queries through Comments for quick replies!