Originally Posted by 3X0
I'll be the first to admit that I have a fairly limited understanding of what such factors mean in practical applications (i.e. outside of circuit topology theory and conversation topics for electrical engineers).
In particular I'm unsure of the implications of damping factor and slew rate in the electrostatic realm.
That's why I'm genuinely curious as to how and when the theoretical limits of electrostatic amplification might be breached, particularly from individuals who have first-hand experience with such audible distortion/clipping. This is not just for something like a SRM-252S or SRM-323S or SRM-T1, but also for justifying the increments from a KGSS to a KGSSHV to a BHSE to a SRM-T2.
I have the money for just about anything short of a SRM-T2/DIY-T2, but I just can't justify the outlay. Let me say that my first-hand experience with the KGSSHV was less than revelatory.
The slew rate is how fast the output voltage can change. If you ever hit the slew rate limit, there is substantial distortion because the output can't "keep up" with the input. You shouldn't actually ever be breaching this if the amplifier is properly built for the load it drives. I measured my Blue Hawaii's unloaded slew rate at about 125V/uS (it is entirely possible the BHSE has superior slew rate, I didn't spend a whole lot of time tuning my DIY BH for slew rate, and the published schematic has typos so every DIY BH is going to be a little different). This means that at full 800Vp-p output, there is no slew rate distortion up to 50kHz. I always forget to measure it with headphone load when I have it in the shop, but it is safe to say it's going to be quite a bit lower.
Basically, since the slew rate limit is caused by the amplifiers inability to provide sufficient current to the load to slew its voltage. Since the current required to slew a capacitor is proportional to the capacitance, adding more capacitance will directly decrease the slew rate of the system.
I think it was stated that slew rate doesn't matter, because it actually doesn't unless you're hitting the wall. At reasonable volume levels with a reasonably quality amp, you're just not hitting the slew rate limit. But the thing is, if you start adding long cables and multiple headphones, you might. Now, that's not to say there aren't other forms of distortion caused by increasing the capacitive load. But calling any of those slew rate limitations is an incorrect use of terminology.
It blows my mind that industry standard is to put two output jacks on electrostatic amplifiers. It is completely absurd to listen to an amplifier with two headphones attached. Sure, this might not matter on a T2, but just about everything else including the Blue Hawaii does not have enough power to recklessly be throwing away slew rate and capacitive loading distortion. I believe it started as amps having two jacks, one pro bias and one standard bias, and now it just kind of stuck because your amplifier would look worse with only one jack. But in fact, the second jack should NEVER be used if you care about sound quality. Those of us who build electrostatic headphones have noticed that etching away even one or two square inches of unnecessary stator area affects the sound produced, especially in the trebles where the slew rate is much higher. Now add a second pair of headphones...