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In Reply to: RE: Actively Triamping Magnepan ribbons..do you protect them or not ? posted by Satie on July 21, 2015 at 21:11:24
I hope you're not suggesting removing the 1.12mH inductor and leaving the 12.1uF capacitor in place. That will not work.
Dave.
Follow Ups:
I was talking of replacing the inductor with a line level RC LP - is the shunt capacitor on its own not going to do its function as a pole in the LP filter because it would be a HF short for the amp?
So the only choices are to run the entire 2nd order LP filter at line level or to leave one smaller value inductor for the second pole and reproduce the original inductor's pole in the PLLXO.
Correct. The shunt capacitor will no longer perform its function if the inductor is removed.
You need to be much more careful with your advice here.
Cheers,
Dave.
IMO, I don't think that a cap is needed for protection with a well-behaved amplifier (no dc offset). The best protection for the tweeter is to multiamp, isolating the tweeter from clipping caused by large power draws by the woofer. But just for my edification, would a shunt inductor (say 0.47 -1 mH) provide the same protection as a series cap but shunting low frequency rather than blocking it with the advantage that signal of interest would not be going through any extra devices.
Edits: 07/23/15
I agree. A series capacitor is not preferable and the best safety device for direct connection to a true-ribbon is the amplifier itself. It needs to be well-behaved at turn on/off and exhibit no DC offset. A series capacitor could still allow significant thumps (the larger capacitor the worse the thumps) to the tweeter on amplifier turn on/off. The only thing it will accomplish is to block steady-state DC.
A shunted inductor will not accomplish the protection goal either. A thumping amplifier (that's a good voltage-source) will still happily deflect the tweeter even though the impedance of the inductor is much lower than the tweeter at low frequencies and DC.
Also, some amplifiers may not like the short circuit at low frequencies.
Cheers,
Dave.
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