Clip Indicator (LED) for Any Power Amp




Introduction: Clip Indicator (LED) for Any Power Amp

About: Music: my profession for over 40 years... Electronics: my beloved hobby always.

A power amplifier cannot deliver an output wave wider than its power supply voltage. When you reach the limit, increasing gain may sound louder but sound will be distorted and can even damage speakers .This simple clipping indicator circuit will announce with an LED that you have reached that limit.

Step 1: Circuit Diagram & Main Components

Q1 BC547NPN transistor

Q2 BC557PNP transistor

D1-D3 1N4148diode

note: If your amp V+ voltage is higher than 45v use BC546/BC556(up to 65v) or other higher voltage ones.

also increase R4 for a led current of 30mA. ( R=v/a )

Step 2: Q1: Emitter Follower

Step 3: Q2: Led Driver

Step 4: C1: Peak Hold

For longer "peak hold" time increase R3 up to 100K

Step 5: D1-D3 Voltage Drop

Step 6: For More Datails, Watch Video. Thank You!

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32 Discussions


First of all thank you very much for the video and the help. But I would need a circuit for my car audio amplifier class A / B (2 channels) 2x800w 1X 1500 Wrms at 2 ohm.

I have read your website since there are people who asked for an 800W amplifier and the scheme varies. but I still do not know how to draw a scheme for my amplifier (since the 800W boy sent another circuit, mine guess it will be even bigger).

I would appreciate the help.

How to make amplifier limiter on relay, that turns off speaker then amplifier is overloading?

Hi I designed a PCB according to the improved version of this clipping indicator. I have a peak rail voltage of 82v-0-82v and when the amp loads to full just before clipping the supply sags to around 70v. I also built an opposing circuit to go with the negative rail so that I can monitor both channels. I changed the transistors to 2N551 and 2N5401. These can handle 160v. My problem is that the clip indicator is very sensitive on the input and even if I touch it with my finger the led lights up. One other problem is that as I go beyond 30v on the rail voltage the led starts to light up prematurely and the difference between the rail voltage and speaker input voltage starts growing and goes beyond 15v or more. Have you some advice how can I correct this. Thankyou

hi! i have read the comments but im sorry to say that i still dont know how to connect this to a subwoofer amplifer. so the v+ goes to 12v+ in the input of the amp, the v- go to ground or battery negative pole? and the "from power amp output" is one off the speaker outputs? but which of them? + or -. i have not built one but if it works and is preatty simple, i migth do, but im not very good at circuitry. but i maybe send to someone more professional to build to me. but i really want this to work on my car amplifier!

1 reply

Speakers use AC like your house, not DC like a battery. So with AC there is no + or - unless you're concerned with Phase, either side of the speaker will work.

Hi, nice work on your circuit design... few questions...

It would appear the LED is only lit while the output is clipping, if that is for fractions of a second then the led may not be visible... would i be correct to say adding a capacitor between the LED anode and the 0v rail will allow the led to stay lit while the capacitor discharges through the LED?

if i want to connect this clip indicator with a car audio amplifier i have to find the internal power supply output or it has another way like a portable oscilloscopebut instead of monitor we can user led just to tell us if the output is not clean???

2 replies

Can you describe components parameters ?
Voltage of capacitor and led, and power of input resistor ?
Input voltage in my case is 25V. Output amp power 150W

So I just checked on a scope and noticed that the clip LED comes on slightly prematurely, is there any way of fine tuning when it comes on? maybe increasing the value of R4 will reduce the diode current so that it doesn't drop as much forward voltage?

1 reply

OK I scoped the saturation voltage of the LM386 and the top transistor is the worst with 1.9v across it when it clips, should this be what I aim for when selecting the top LED/diode series string?

Could I replace the x3 diodes with a single LED? As the circuit continuously drains several milliamps but putting a power indicator LED in there would put that current drain to good use especially when powered by a battery.

2 replies

Hi! yes you can, but make sure the forward voltage (Vf) drop of the led is close to 2v. Lower Vf, and indicator wont light. Higher Vf, and the indicator will light prematurely.

in this chart you will find the typical Vf´s of different color leds.

Greetings & thanks!

Oh that's handy then, a green LED will drop around 2.1v which is very close to the 2.2v I measured being dropped by the diodes.

I just signed up to say that I made this and it works great with my crappy little LM386 amp. Its easily one of the most underrated audio instructables around.


1 year ago

i already build this but i have a problem whenever i connect it to my amp. the led lights turn on steadyly how do i properly connect it from the power supply (30 o 30) vac toriod transformer thanks in advance!

1 reply

HI! in this same comment section you can find a reply (7 months ago) to your question. That circuit diagram is suitable for your amp (higher voltage supply). In that case it was +30V / -30V. Extreme caution when opening your amp as you will have around 85v between + and - rails. Capacitors may hold the charge for a long time even after disconnecting the amp from the mains..

Nice tut. Just wondering, in the 80's some speaker cabinets (see photo on the right side) got a overload indicator, any idea's how these work?

1 reply

Another one that got this feature, it is a passive speaker (like the other example), not an active one.

technics sb-r3.PNG