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Yes, let's talk about low pas LCLC filters.

Hi.

In switching amps, the low pass filter can cure or kill the sonic performance of the amp. It plays the crucial role of removing the triangle high frequency carrier (say switching frequency of 100KHz & up up), plus its multi high order harmonics & permitting uncontaminated continuous music sine wave signals to pass to the loudspeaker load.

We are talking about some 1A no-signal current & full load currents of many amperes at over 100KHz, depending on the rated O/P power of the amp.

Wires of large size & of very low skin effect material must be used in the inductors to prevent high frequency loss along with high permeability large ferrite cores adequately gapped to prevent core saturation & for linear B/H operation.

Unlike linear/analolgue amps handling only audio signals, momentary no load, like loudspeaker wires detached, can generate large enough voltage monentarilly at the junction of the filter inductors to push the cores into saturation, blowing the filter caps, & could even blow the switching power transistors.

The choice of the inductor leads to receive the input signals is critical to reduce capacitance induced RFI. So effective RF layout of the low pass filter is very helpful.

The filter capacitors must be high voltage (up to 100VDC) for the reason above, & high Q to handle min 100KHz. So non-polar multi-layer film caps should be used.

Again, design of the low pass filter is normally based on a fixed norminal resistive dummy load of say 8R. The reative impedance of any loudspeakers swing up & down like a yo-yo. This makes the design of a proper low pass filter more complex.

To anwer your question, anywhere upstream of the low pass filter is digital where loop feedbacks should be executted for data correction & control.

c-J


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  • Yes, let's talk about low pas LCLC filters. - cheap-Jack 08:21:16 08/25/06 (0)
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