catman Posted May 23, 2017 Share Posted May 23, 2017 G'day all, a technical question for anyone familiar with the present range of Cambridge Audio integrated amplifiers and whether the line level inputs are DC coupled without capacitors. For a while I've noticed my CA amp in here apparently going into intermittent shut down and the muting (protection) relay operating for no apparent reason. I have one of my DIY AM detector boards plugged in to one of the 'line' level inputs and I've realised that there is a small DC offset present on the output, and I wonder if this might be causing the intermittent amplifier shutdown if the CA line level inputs are direct coupled without DC blocking capacitors. I am now more suspicious of this possibility as I am presently using another AM detector that does include an output blocking capacitor, and so far this strange shut down fault hasn't appeared, so I am wondering about this possibility. Any thoughts or comments? Regards, Felix. Link to comment Share on other sites More sharing options...
eltech Posted May 23, 2017 Share Posted May 23, 2017 (edited) If the problem only occurs with one particular source (the DC coupled AM detector) then you are probably correct about your your reasonable assumption. Edited May 23, 2017 by eltech 1 Link to comment Share on other sites More sharing options...
PonyTail Posted May 23, 2017 Share Posted May 23, 2017 Felix, just measure the DC offset at the amplifier output. Any offset will cause DC to flow in the speakers and cause excessive amplifier power dissipation, not to mention the heating and possible destruction of your woofer voive coils. Link to comment Share on other sites More sharing options...
catman Posted May 23, 2017 Author Share Posted May 23, 2017 G'day all, yes I've just done that and there is a solid 9 Volts DC offset on the detector output, and higher than I thought it was. So I've just soldered in an output capacitor so I'll see if the fault recurs with this detector now. Interesting. Regards, Felix. Link to comment Share on other sites More sharing options...
andyr Posted May 24, 2017 Share Posted May 24, 2017 On 23/05/2017 at 5:44 PM, catman said: G'day all, yes I've just done that and there is a solid 9 Volts DC offset on the detector output, and higher than I thought it was. So I've just soldered in an output capacitor so I'll see if the fault recurs with this detector now. Interesting. Regards, Felix. 9000mV - WOW!! AIUI, offsets should be < 10mV - certainly no more than 20mV. Andy Link to comment Share on other sites More sharing options...
Addicted to music Posted May 24, 2017 Share Posted May 24, 2017 16 minutes ago, andyr said: 9000mV - WOW!! AIUI, offsets should be < 10mV - certainly no more than 20mV. Andy Just as well it looks like the CA has protection by shutting down. Link to comment Share on other sites More sharing options...
catman Posted May 24, 2017 Author Share Posted May 24, 2017 G'day all, well the output capacitors seem to have completely solved the problem, no more amplifier shutdown, and I could be imagining it but things also seem to be sounding better now. Is that possible? Regards, Felix. Link to comment Share on other sites More sharing options...
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