I have a friend's Denon AV receiver which I am testing at the moment. It is rated at 65W/channel "DIN" power rating 1kHz into 4R. I have the schematic and the supply rails for the amp section are shown as +/- 46V (no load, no signal) and these are the value I get with no load/no signal
. When I run a 1kHz sine wave through for testing, with an 8R load attached, it starts to clip at 23V peak-peak, or around 12V peak, way less than the 46V rail. The rails at clipping are still +/-45V. From my calcs this would imply an RMS power rating of only 9W into 8R. This amp has blown a couple of woofers.
Any suggestions as to why it would be clipping at such a low voltage and how does the power I am measuring at clipping equate to the rated 65W?
Thanks
. When I run a 1kHz sine wave through for testing, with an 8R load attached, it starts to clip at 23V peak-peak, or around 12V peak, way less than the 46V rail. The rails at clipping are still +/-45V. From my calcs this would imply an RMS power rating of only 9W into 8R. This amp has blown a couple of woofers.
Any suggestions as to why it would be clipping at such a low voltage and how does the power I am measuring at clipping equate to the rated 65W?
Thanks
i work on Denon AVRs all the time. try measuring ALL of the channels. you will find that some of the channels clip at 23Vp-p and some at 90V p-p. i haven't had the time to find out why. i work in a production environment, and don't get a chance to dig into some of the "whys" of various designs unless the amp seems to be misbehaving in that particular area. i will check further. it may have something to do with the DSP "preclipping" the signal. center channels are usually the ones to clip at full output, with the rest "scaled down" according to their relative levels. this way, all channels clip at the same time, rather than having the center clip first, and then the others. at least that's what it seems like when i check surround amps.
Thanks for the response. This is a simple 2 channel receiver and both channels seem to be the same.
Check the voltage on the supply rails going to the voltage amp stages.
The RC decoupling feeding these may have gone faulty.
R gone high resistance or C gone open circuit.
The RC decoupling feeding these may have gone faulty.
R gone high resistance or C gone open circuit.
check the voltage output from the +/- 15V regulators and check R105 which is the dropping resistor for both diff amp's negative rail. one other question..... did you check the rail voltages with the same oscope you measured the output waveform, or did you measure the rails with a meter? the reason i ask is that one thing that happens often, is that the oscope input channel variable gain pot (usually the middle knob in the input attenuator) gets nudged out of it's "CAL" click stop, and so all voltage measurements are incorrect.
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