The speaker has a pop sound

When I add the Zobel circuit, the speaker will make a popping sound like this.
And this is my circuit.


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The purpose of a Zobel network is to prevent the amp's output seeing a light or inductive load at very high frequencies, which could lead to destructive VHF instability of the output stage itself. It's needed with non-global-feedback amps too.

It must be before any inductor for this reason, and as close to the output devices as you can make it. 100nF is plenty, do not use more or you may burn out the resistor. The resistor should be about the nominal amplifier load, so 10 ohms for an 8 ohm amp is commonly used. Thus at very high frequencies this resistor is seen as the main load, making it definitely resistive upto 100MHz or beyond. This prevents the output stage from being an inadvertent RF oscillator.

A 22uF capacitor will likely be inductive at VHF and allows the audio signal to heat up the resistor excessively. Use 100nF unless you have a very good reason not to.

The inductor (air-cored, several µH) is to avoid the amp seeing an overly capacitive load from long cables, which can oscillate the GNFB loop by adding more phase shift. This is not needed if there is no global feedback loop.
If open the DC power supply ( 16V ,- 16V , 0.4A , 0.4A ) About 0.25V.
With speaker connected, the output offset should not be more than maybe 50mVDC.

As there's no popping without signal, I wouldn't worry.
After all you're switching in and out a small extra load.

Use the Zobel values 0.1µ/10R as recommended above.
Should also lower the popping.

Last edited:

Deleted member 550749

R u trying to boost wattage from lm1875 by adding another output transistor, if yes then shearch for propper schematic , don't play with this beautiful ic otherwise that gonna fry 😉 search , search, search until u get the proper one or two some expert, who makes amp like this, circuit is basic opamp direct coupled amp but I thing there will be more circuitry