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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Update - HELP!! Amp oscillation!! posted by tlenthe on March 26, 2005 at 17:41:44:
you get an HF oscillation because the capacitive load of you cable gives a marginal stability to your amp, which, when interacting with the load as seen from the amp, gives way to this oscillation. So:
(1) fix it VERY SOON, as the oscillation can be very strong, even unnoticed from the output (because the two legs of the push-pull can oscillate in opposite directions, so, you won't see anything at the output) can make the transistors very hot, and you can get destructive runaway. And no protection circuitry will protect the transistors, as this protection circuitry is often high-cut filtered in order to avoid triggering on benign short peaks.
(2) the Zobel you installed does not alleviate the problem: the amp always sees the capacitive load of the cable, Zobel or not.
(3)you need a load in serie with you cable in order to mask the high capacitance of the load. Take a big 10W 4.7 ohm resistor, solder one end of a1.5mm enamel wire (motor store), wind 5 to 10 turns around the resistor, and then solder the other end to the other end of the resistor. So, you get a resistor of 4.7ohm in parallel with a 2 to 5 microhenry inductance. Solder it in serial with the hot wire of your speaker cable, on the amp side, not the speakers. Some thermoretractile tubing around the stuff to make it aesthetic and pleasanty looking, and it should work. Let us know ;-)
(4) zobel values. Another day, I'm tired and still have homework. Anyway, your values seem correct, for a single speaker (I'm a multiamped system afficionado!)
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Follow Ups
- Re: Update - HELP!! Amp oscillation!! - Jacques 08:37:42 03/27/05 (1)
- Re: Update - HELP!! Amp oscillation!! - djk 17:03:04 03/27/05 (0)
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