I have built a number of Naim NAP250 clones with 20Ω Draloric AC wirewound resistors in their Zobel networks (as in the originals, I believe).
But I've recently understood that their inductance can swamp their resistance at high frequencies, and if said high frequency is less than the fT of the output stage then you've essentially got no Zobel network for half of each cycle.
So I thought I'd better find out what the inductance of my wirewounds is. Of course the datasheet doesn't spec it. 🙁
Being that I'm in no great hurry I fired off an email to Draloric/Vishay. This was around 11pm on a Sunday.
I get a reply at 5am Monday morning: 0.26µH. Now that's customer service!
(And for those of you curious my resistors turn inductive at a bit over 12MHz. Probably another reason NAP250's had a tendency to fail with no load hooked up.)
But I've recently understood that their inductance can swamp their resistance at high frequencies, and if said high frequency is less than the fT of the output stage then you've essentially got no Zobel network for half of each cycle.
So I thought I'd better find out what the inductance of my wirewounds is. Of course the datasheet doesn't spec it. 🙁
Being that I'm in no great hurry I fired off an email to Draloric/Vishay. This was around 11pm on a Sunday.
I get a reply at 5am Monday morning: 0.26µH. Now that's customer service!
(And for those of you curious my resistors turn inductive at a bit over 12MHz. Probably another reason NAP250's had a tendency to fail with no load hooked up.)