Mystery RC circuit in TS482IDT Audio Amplifier.

[Kenny03]

Hey,

I'm currently working on upgrading an audio amplifier design I inherited. I've gone through the circuit in detail and I think I've got a handle on most of it. But I'm stumped by the purpose of the highlighted RC circuit. Anybody have any ideas on why it's there? Or maybe could point me in the right direction to figure it out?

Cheers,

 

[AScha.3]

This RC present a RF load, to prevent Oszillation of the amp.

 

[Piranha]

Also those high-pass filters are set to 13263 Hz, which is somewhat suspicious.

[LCE]

It's easier to understand if you see the source impedance (okay, very low resistance and inductance), then it becomes a low pass filter.

The resistor mostly reduces the "direct" capacitive load for the amplifier.

Corner frequency in this configuration rather depends on the amplifier's impedance with the 100 nF cap, so it will be quite high, assuming low Z output.

If that's really needed is another question... I'd rather expect the snubber directly at the DAC or class-D output.
Maybe that amp needs it in non-inverting configuration.

And make sure to not use any ceramic caps, except for NP0.

[Kenny03]

Thanks for the tips. The 13kHz cutoff is indeed low but probably has to with the fact that this audio circuit is only used for voice and words, not music. Hence why it's not the full 20kHz.

Also, Curious to know why not x7r ceramic? but yeah the current capacitor is ceramic x7r.

[AScha.3]

1. there is no cutoff ! this R-C is just a Boucherot cell

https://en.wikipedia.org/wiki/Boucherot_cell

2. just for hi-end audio class2 ceramics making some 0.1% distortion , if used for coupling.

but here you use it for Boucherot_cell and not coupling and not hi-end-audio, so your x7r is perfect here.