@jwpstayman - I am simply relating to my experience with Naim amps
This NAIM forum thread states the problem quite clearly
- I believe Mike B. works for NAIM
Mike-B1Jun ’19 anon64018693:Question is: what is the electrical purpose of approaching Naim’s recommended values, notably for inductance? Is it exclusively to provide compensation for the lack of inductor coil or does it also allow the amplifier to express itself more comfortably in terms of musicality?
Solid state amplifier output stages become unstable due to capacitive reactance. The effects can be audible distortion caused by low level ringing up to the output devises overheating and in some cases destroyed.
To counter this all solid state power amplifiers have a Zobel network across the output stage to damp this oscillation; the conventional Zobel circuit consists of a series capacitor and resistor with values around 100nF and 10 Ohm. The capacitor begins to conduct as frequency rises and the 10 ohm resistor becomes the damping element shunting the circuit Q. With the variable capacitive reactance of the speaker load coupled to a length of speaker cable the Zobel circuit alone may not be enough. This is commonly solved by placing an inductor in series with the amplifier output downstream from the Zobel shunt circuit. The inductor value is set low enough to avoid high frequency roll-off in the audio range but high enough to provide the required damping at frequencies above that.
Amplifiers with a series inductor can use any type of speaker cable, however with a high inductance or excessive length of cable added to the amplifiers internal inductor it risks some roll-off at high frequencies.
Some manufacturers such as Naim do not have an internal inductor and choose instead to use only the speaker cable to provide inductance.
ALSO as stated above - the acquaintance that experienced the oscillation issue when he damaged his Ayre amp using the TOTL (high capacitance) CARDAS speaker cables. He also damaged a loaner Gryphon amp immediately after using the same cables.
Once the unit was repaired he used lower capacitance speaker cables without any issues.
BTW - The Cardas cables were also tested for short circuit and none were found
Coincidence? I do not believe so !
Mis-information? I do not believe so !
But if people want to try this for themselves - Good Luck, but don’t say you weren’t warned !
I do concede that not ALL Cardas speaker cables have sufficient capacitance to cause oscillation issues
But this issue IS NOT a problem for NAIM amps only.
Regards - Steve