I could be wrong. Appears that bass gets more prominent after 3 hours with Pass Xa 100.8. First hour bass is a light. Then up to 3 hours sounds in good proportion to rest of frequencies. Thereafter bass becomes over prominent up to 100 hz. Does anybody have similar experience.
Hi alfa100,
I have a XA160.5 driving Wilson Sasha speakers and have experience a similar effect and have a possible solution. Here is some information to set up my findings. Your XA100.8 like my XA160.5 are both class A amplifiers that for all practical listening levels will always draw the same amount of current from the power line. Let’s call this MAX current draw, since it is likely not going to be higher for any practical listening levels.
The Pass Labs amplifiers are designed to run at around 53 degrees C on their heatsinks. The reason for this is that the MOSFET output devices sound their best at that temperature. This is why the amplifiers take about 3 hours to start sounding their best coming from standby. It takes that long for the mass of the amplifiers and heatsinks to get to a stable temperature equilibrium with the ambient temperature of the room. During this time the power system powering the amplifier is also gradually heating up given the amplifier is drawing MAX current all the time. The power cords, outlets and any downstream conditioning equipment (in my case a 5 KW isolation transformer) are also heating up gradually.
In my system I observed significant sound quality (SQ) improvement during the 3 hours during amplifier temperature stabilization, then slower SQ improvement to the fourth hour, but then in the fifth to sixth hour the system started losing SQ and sounded less detailed. It had a warner overall balance that was not as neutral sounding and loss of bass definition. Your XA100.8 having very different feedback may manifest the bass difference differently your power system difference I found in my system that was the culprit.
I was using Porter Port AC outlet for the power amplifiers. I believe it was warming up over time and the grip on the AC plugs was relaxing. To use my ISO transformer in a balanced power configuration it forces me to have only one output; thus, one outlet for both amps. The MAX current draw of both amps on that single outlet causes a lot of heating compared to if I only had one amp plugged into it. Since heating is a current squared times resistance relationship if I had two separate outlets the heating effect would be 4 time less.
So what was my solution? I replaced the Porter Port with an Oyaide R1 outlet. I’m not going get into the fact that the Oyaide R1 outlet sound different than other outlets and took a significant amount of time to break in. I’m going to make the point that the Oyaide R1 has a better grip than most outlets and that the degradation of SQ that I heard in the fifth to sixth hours of operation with my XA160.5 has gone away in my system with everything else being the same. I seldom have the amps on for more than 10 or 12 hours at a time, so I cannot speak to running times longer than that. I do not notice SQ changes anymore for the longer periods I have the amps turned on has been my experience.
My next move is to implement a different ISO transformer that has 3 separate 20 Amp balanced outputs, which I will be able to have a separate 20 Amp outlet for each mono amplifier.
Hope this helps if you might be experincing the same issue....