John Curl's Blowtorch preamplifier part II

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A good design allows for no obvious added inductance. Of course you have the wiring to the output of the case, AND you don't expect anybody to do anything STUPID, like put the precise worse case value of capacitance directly on the output of the power amp internally. Almost anything can at least be made to ring, if not oscillate.
However, decades ago, I was shown in a personal demonstration by a colleague that even 2uH could be audible, so I elected to lower its value as far as I could.
And THEN the Taiwanese designers had succeeded in using NO obvious output inductor in one of their prototypes, and we progressed from there.
The ONLY seeming drawback that I have found is that super fast designs that could have 500V/us or so, only to have 150V/us or so. This seems to be the tradeoff. I think that Nelson Pass would agree with me, as he did it first.
 
Think 1 pr represents much , try these on for size ... :)
 

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Oscillation detector?

Yes, only Zobel.
Zobel to flatten impedance

I usually omit zobel, or use minimal value of capacitor (22nF). If this zobel is to flatten impedance, isn't it speaker designer's decision to give one (on the tweeter) or not? Giving one in amplifier output seems a bit of gambling.

Zobel or resistance, at amplifier or at speaker?

At speaker, we can put the component on the right driver. For example, critical is to put resistance in series with woofer and not with tweeter. I have many flat/foil inductors but I think I will never buy such coil again. Low DCR is a good think when too sensitive tweeter is an issue, but I found extra resistance in series with woofer is a good thing sound wise.

Zobel for oscillation protection

I don't know if it is effective to ground the VHF signal, to protect oscillation from happening, so how about a led indicator that is lit up when enough current is flowing thru the zobel resistor. By this, amplifier user is helped to avoid giving bad loads to the amplifier. Why it is not done in commercial amps, what is the issue?

ADD:

I forgot there's already speaker protector?
 
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