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Junior Varsity
Power amplifier sensitivity question....
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<blockquote data-quote="Michael John" data-source="post: 4058" data-attributes="member: 830"><p>Hi,</p><p></p><p>I've been looking at various power amplifier specs and I'm wondering why amp manufacturers quote really large maximum input levels?</p><p></p><p>Here's an example using manufacturer supplied numbers for a QSC PL325:</p><p></p><p>The rated input sensitivity is 1.2 Vrms (approximately +4 dBu).</p><p>The rated amp gain is 34.5 dB</p><p>Therefore for a sine wave @ 1.2 Vrms, the output voltage will be 63.7 Vrms or 90 Vpeak.</p><p>63.7 Vrms into 8 ohms is approximately 507 Watts RMS. This matches the QSC quoted number of 500W into 8 ohms (EIA 1 kHz 1% THD).</p><p></p><p>Now here's the problem.</p><p></p><p>For a 1.2 Vrms input sensitivity, QSC states a maximum input voltage of 11 V. (I assume peak.)</p><p>Using the rated amp gain of 34.5 dB, this input peak equates to an output voltage of 584 Vpeak.</p><p>Clearly the amplifier's output cannot go this high.</p><p></p><p>This is a class H amp and I guestimate that the maximum output voltage is a little above the 90 Vpeak from above, but nowhere near 584 Vpeak.</p><p></p><p>In reality, the amp will clip with input signals only a fraction larger than the 1.2 Vrms input sensitivity. So why the maximum rated input of 11 volts?</p><p></p><p>Is amp output clipping somehow preferred over the input circuit clipping?</p><p></p><p>[These calculations are for the 1.2V input setting, but the questions still arise for the 32 dB and 26 dB settings.]</p><p></p><p>Best,</p><p>Michael</p></blockquote><p></p>
[QUOTE="Michael John, post: 4058, member: 830"] Hi, I've been looking at various power amplifier specs and I'm wondering why amp manufacturers quote really large maximum input levels? Here's an example using manufacturer supplied numbers for a QSC PL325: The rated input sensitivity is 1.2 Vrms (approximately +4 dBu). The rated amp gain is 34.5 dB Therefore for a sine wave @ 1.2 Vrms, the output voltage will be 63.7 Vrms or 90 Vpeak. 63.7 Vrms into 8 ohms is approximately 507 Watts RMS. This matches the QSC quoted number of 500W into 8 ohms (EIA 1 kHz 1% THD). Now here's the problem. For a 1.2 Vrms input sensitivity, QSC states a maximum input voltage of 11 V. (I assume peak.) Using the rated amp gain of 34.5 dB, this input peak equates to an output voltage of 584 Vpeak. Clearly the amplifier's output cannot go this high. This is a class H amp and I guestimate that the maximum output voltage is a little above the 90 Vpeak from above, but nowhere near 584 Vpeak. In reality, the amp will clip with input signals only a fraction larger than the 1.2 Vrms input sensitivity. So why the maximum rated input of 11 volts? Is amp output clipping somehow preferred over the input circuit clipping? [These calculations are for the 1.2V input setting, but the questions still arise for the 32 dB and 26 dB settings.] Best, Michael [/QUOTE]
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