bizarre turn on humm-pop

[mazurek]

I have a bizarre problem related to the sequencing of turning on my active crossover, amplifiers and preamp.

If the active crossover is turned off, and then the crossover and amplifier are turned on, when the preamp turns on there is RFI sounding noise, and then a pop which moves the drivers out visibly.

If the crossover stays powered, there is no problem when turning on and off preamp/amp. This problem is always repeatable if the crossover is turned off and on when the amp/preamp are turned off. If the crossover is ommited entirely, there is no turn on issue. My other equipment is adcom preamp, and ucd power amps. I'm sure the crossover's turn on transient is not the problem, I can turn it on way ahead of time and still replicate the problem.

The active crossover has a opamp buffer stage to begin with, and 10kohm input resistance (I ran out of 100kohm and will order more). No dc should be reaching output, as all drivers have some highpass or rumble filter, output is straight from last filter stage through 200 ohm resistor to rca connector. There is no turn on/off muting in this version, but I still have problems even if I turn the crossover on way ahead of time. The crossover ground is connected to the power supply ground - connected to earth ground at one point. This problem is replicated with and without power supply ground connected to earth ground.

I am completely perplexed as to why this would happen. I eventually will upgrade the crossover to provide muting,etc, but am not sure this will fix the problem.

I believe the seas 27tdfc are very well made because my crossover abuses it a lot.

Thanks for any insight.
Lee

[pinkmouse]

Simple solution, just turn your power amp on last.

[mazurek]

I figured thats what people would say.

I was trying to automate everything easily with a 12volt trigger switch, but I think my preamp turns on its trigger too soon, maybe I need to mod the trigger switch with a delay circuit.

Psychologically, I hate leaving all the electronics I built plugged in all the time, it feels like I'm going to burn down my house.

Lee

[mazurek]

Well, apparently when the crossover turns off, it builds some crazy transients on the output. I guess dc potential remains on the circuit forever until the thing turns on again. The outputs are not grounded, so I guess the potential stays on forever. I would have thought that referencing the inputs to ground with a resistor would bring down the dc offset quicker when it turns on.