Hi Randy
You've got great advice from everyone in this thread about troubleshooting circuits but as I thought it might be worthwhile taking another look at the amp itself. I've never heard it so I checked the specs which generally look pretty good but this commentary about the signal to noise ratio caught my eye. As we all know the M80s are very transparent because they are so linear so those tweeters will be more sensitive to any HF noise. The following discussion was from the Audioholics article. Gene DellaSalla's measurements showed an unflattering noise profile for this amp.
"Signal to Noise Ratio (SNR) Measurements
Measuring the Signal to Noise ratio of this amplifier proved to be quite challenging due to the lack of proper LPF for limiting the bandwidth to below the switching frequency.
By applying A-weighting response curve, I was able to achieve partially reasonable measurements of 82dBA (A-wt) at 1 watt or about 102dBA at 270wpc.
From Emotiva Engineering Labs:We perform my signal to noise ratio test a little different than you do. We base our measurement strictly on the rms voltage as measured on the AP with a <10Hz to 30Hz bandwidth selected. No other weighting is applied. The amplifier is connecting to a purely resistive load, in this case 4 ohms. We measured a noise floor voltage of 268uV using the balanced output of the AP with a 50 ohm output impedance - generator selected to off to terminate the input to the amplifier. From this starting point we let the AP do all the work. We select the output level from which I want the S/N ratio to be referenced at and call that the 0dB point. Below are some measurements we have taken:
102dB ref 300W
101dB ref 270W
87 dB ref 10W
77dB ref 1W
These numbers should be more consistent with what you are hearing from the amplifier. Also, we believe these numbers represent a best case scenario because we are using the balanced input. The key to this test is the noise floor of the amplifier. This can change significantly if power cables are inducing 60Hz into signal, other equipment could be radiating noise, etc.
In any event, the 77dB @ 1 watt number isn’t flattering to say the least, but given the unique amplifier topology, I suspect the out of band switching noise is producing a non representative number since noise was never an audible issue in real world listening tests. When using the Yamaha RX-V2500 as the preamp for the Emotiva MPS-1, the set-up was dead quiet and sounded as silent as other amps I have measured with significantly lower noise floors. "
I also noticed that he ranked the signal to noise ratio lowest among his performance parameters. I know you tested the Denon as well but it may be worth focussing on the amp itself as a noise source. Sometimes its a compatiblity issue with the pre-amp. If you were nearby I'd lend you one of my Brystons for comparison.
http://www.audioholics.com/productreviews/avhardware/emotivaMPS1p5.php
