Why does my system now have shrill top end.

Kosst, my hypothesis is not predicated on the cables having changed in any way whatsoever. If it wasn’t clear, when I referred to the condition being "sufficiently marginal that minor aging effects or perhaps even a change in AC line voltage have put it over the edge," resulting in ringing or oscillation, I was referring to minor aging effects in the amplifier. Which in turn might have made the amplifier more prone to ringing or oscillation as a result of the heavy capacitive load.

Admittedly, though, the fact that both channels are exhibiting the problem does **somewhat** lessen the likelihood of my hypothesis accounting for the problem.

Also, Peter (Pbnaudio), thanks for your comment. As many here are aware, Peter is a highly experienced designer of well regarded audio electronics and speakers.

Regards,
-- Al

Have your listening habits changed? My system sounds much brighter if I listen when I’m fatigued/tired.

Otherwise, it’s most likely that your amp needs service, or you need to listen with a Shakti stone taped to your head.

@almarg 

I would be genuinely shocked to discover a Pass XA30.8 exhibiting ringing. Nelson believes in wide bandwidth but also takes great care to avoid ringing in his amps. He once built an amp at Threshold that became unstable into cables such as we're describing and it released the magic smoke. Since then he's made it a point to avoid designs with that possibility. The F5 is an exception to that where he specifically warns against exotic cables that are good at transmitting high frequencies, like Litz wire, because of the DC-1MHz bandwidth of the amp. I suppose it's technically possible something could fail to allow that, but I think we'd be talking about a short or a resistor failing closed and that would lead to far more drama than a shrill top end. 

I have not read every post in this thread, but how old are you, and have you ruled out hearing loss? - Gerry

Al,

I agree the speaker cables should be replaced with something else to conduct a test. The most the OP will be out is a few bucks and a little of his time. The OP can pick up something cheap speaker cable at Best Buy or Home Depot.

Al,

What are the chances the OP could connect the Linn Linto Phono Preamp directly to the inputs of the Pass amp without it playing too loud for a test. That would take the Pass XP 20 out of the equation.

SPECS

Input connectors: gold-plated direct circuit board mounted RCA jacks
Output connectors: two pairs jacks (as above)
Audio input level: 150 microvolts nominal, High Gain
500 , Low Gain
Input Impedance: 150 Ohms, in parallel with 4.7nF
Output impedance: 100 ohms both pairs of outputs
Gain: 64dB at 1KHz, High Gain
54dB at 1 KHz, Low Gain
Power consumption: 6 watts, 12VA approximately
Dimensions: 320 x 320 x 80mm
Weight 1.5kg

https://www.audaud.com/audaud/JUL-AUG02/EQUIP/equip2JUL02.html

Unplug the Pass XP 20 from the power outlet.

 Try the Linn Linto Phono Preamp first plugged into the P5. If the " shill" sound is still present plug the phono preamp directly into the wall outlet. Unplug the P5 from the wall outlet.

Jim