Audio Precision AUX-0025 Switching Amplifier Measurement Filter 

available in the UK from TTi

  Audio Precision AUX-0025 available from TTi in the UK & Eire

  AUX-0025 Switching Amplifier Measurement Filter

  
  AUX-0025 Switching Amplifier Measurement Filter. Click for larger image.

Class D amplifiers use a switching process that adds fast-rising edges at the switching frequency to the audio output signal, presenting a difficult signal for audio analysis.

 
 

The solution is to precondition the signal before presentation to the analyzer using a low-pass filter that reduces the out-of-band switching components (the fast edges) while passing the audio signal intact.

The Audio Precision AUX-0025 Switching Amplifier Measurement Filter is a dual-channel passive filter that provides the necessary attenuation of out-of-band signals.
 

AUX-0025 features

The Audio Precision AUX-0025 Switching Amplifier Measurement Filter is a dual channel multi-pole LRC passive filter that provides the necessary attenuation of out-of-band signals and reduces the steepness of the fast switching edges.

Since all Audio Precision analyzers provide two input channels, the AUX-0025 is a two-channel device. The input connectors replicate the input connectors found on analyzer inputs: XLR female and banana jacks. The output connectors are XLR male. Since loading capacitance is an issue, two short low-capacitance color-coded XLR male to XLR female cables are included for connection to the analyzer.

Switching amplifier output signal, unfiltered                          Switching amplifer output signal, filtered through AUX-0025

Switching amplifier output signal, unfiltered.       Switching amplifier output signal, filtered through AUX-0025.

The oscilloscope traces above illustrate the effect the filter has on the unfiltered output of a typical switching amplifier. The photo on the left shows a signal from a switching amplifier. The photo on the right shows the same signal at the output of the amplifier filtered by the AUX-0025 low-pass filter, which attenuates the out-of-band frequencies to permit distortion, noise and other performance measurements. Notice how the unfiltered signal masks other components modifying the sine wave, affecting the capability of an analyzer to properly characterize the performance of the amplifier.
 
 

AUX-0025 Specifications

AUX-0025 overall response curve. Click for larger image.        AUX-0025 passband response. Click for larger image

AUX-0025 overall response.            AUX-0025 passband response.


Frequency Response: ±0.05 dB, 10 Hz to 20 kHz

Insertion loss: Typically 0.05 dB

High Frequency Rejection: Typically >50 dB, 250 kHz to 20 MHz

Maximum Input: ±200 Vpeak

Interchannel Crosstalk: >90 dB at 20 kHz

Distortion: < –110 dB harmonic (measured at 70 Vpp, 1 kHz)
                < –100 dB IMD (at 70 Vpp with 18 kHz and 20 kHz dual tone test signal. IMD components are at 2 kHz,
                   16 kHz, and 22 kHz)
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Thurlby Thandar Instruments Limited
Glebe Road, Huntingdon, Cambridgeshire PE29 7DR
Tel: 01480 412451  Fax: 01480 450409  Web: www.tti.co.uk  Email: sales@tti.co.uk