I do most of my audio on the cheap, so my current digital media set up us driven with smart phones and small usb/bluetooth dacs. They're designed to drive ear buds, so they usually have filterless class D amps on the output. The dacs are reasonable high-resolution devices, but the outputs are noisy at high frequencies
I use a 100mH inductor when I want to scope signals off of them, but I was wonder if there were "boxed" solutions to filter these types of designs.
Edit: if this post isn't diy enough or class d design enough, I can repost. I am willing to build something, but I also don't want to reinvent the wheel.
I use a 100mH inductor when I want to scope signals off of them, but I was wonder if there were "boxed" solutions to filter these types of designs.
Edit: if this post isn't diy enough or class d design enough, I can repost. I am willing to build something, but I also don't want to reinvent the wheel.
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Boxes which provide standardized low-pass responses for measuring classD amplifiers exist - Audio Precision makes (for example) AUX-0025 : AUX-0025 / 0040 / 0100 Switching Amplifier Measurement Filters - Audio Precision
They do the job very well but they're not cheap.
I wouldn't expect a 100mH inductor to provide much filtering by itself in series with an oscilloscope probe. Partly because 'scopes have high input impedance and secondly because a 100mH inductor is very likely to have a self-resonant frequency below the switching frequency of a classD amp. Meaning it'll look like a capacitor rather than an inductor.
They do the job very well but they're not cheap.
I wouldn't expect a 100mH inductor to provide much filtering by itself in series with an oscilloscope probe. Partly because 'scopes have high input impedance and secondly because a 100mH inductor is very likely to have a self-resonant frequency below the switching frequency of a classD amp. Meaning it'll look like a capacitor rather than an inductor.
If the output's lightly loaded an RC filter is the simplest, perhaps two stage RCRC, with the
R values much less than the preamp input impedance. Designing an LC filter is trickier, but doable, you'll need a suitable load resistance on the output, and find a filter design app, either 2 or 4 pole LP Butterworth at 25..30kHz cutoff sounds about right. If the load is chosen at
30 ohms or so the network could be used with earphones directly too.
R values much less than the preamp input impedance. Designing an LC filter is trickier, but doable, you'll need a suitable load resistance on the output, and find a filter design app, either 2 or 4 pole LP Butterworth at 25..30kHz cutoff sounds about right. If the load is chosen at
30 ohms or so the network could be used with earphones directly too.