Bottlehead Forum
Bottlehead Kits => Kaiju Stereo 300B amp => Topic started by: Larpy on July 20, 2020, 10:50:46 AM
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Not sure if my thread subject is worded properly. Here's my situation: I'm using the Kaiju to drive full range drivers that have a piercing peak at 6.5K Hz. I built a LCR notch filter that shunts the peak frequencies to ground (it's wired across the FR driver's terminals). The Re of the driver is 6.5 ohms, and I've been experimenting with different values of the resistor in the LCR notch filter. I started at an 8 ohm resistor and wanted more attenuation, so I tried an 5 ohm resistor. Better, but can I go even lower? Is there a point where the resistance gets too low for the Kaiju and will make it unstable? I guess I'm wondering if the resistance gets low enough, will the Kaiju think there's a short circuit?
I'm a hobbyist, not an EE, and I confess that I know enough to calculate the LCR notch filter (and to build it) but not enough to fully understand its implications for the amplifier that drives it.
So I thought I'd turn to the experts before I go any further.
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The Kaiju is unconditionally stable. Is there a corresponding impedance bump where that 6.5kHz peak is? You may end up just flattening that out with your network in the end.
Ultimately if you go too low, THD will rise at the notch frequency, but nothing harmful will happen to the amp.
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Thanks for the quick response, PB.
No, there's no corresponding impedance spike at 6.5K Hz, at least according to the specifications given by the driver manufacturer. The driver has a whizzer cone, and I wonder if that accounts for the spike.
What is "too low" in terms of producing more distortion? 2 ohms? 1 ohm? I'm using the 8 ohm tap on the Kaiju's OPTs.
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You could try the other notch filter arrangement that puts the components in series with the driver. This arrangement gives super high impedance at your target frequency rather than low impedance.
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OR you can build a "bridged-T" filter which maintains a constant resistance through the notch.
But to get it right, you should determine the impedance of the driver at 6.5kHz - it will be much higher than 8 ohms in most cases! The impedance is also likely to have an inductive component, in which case a Zobel may be in order.