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Firezog Mod Question


unclej

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as i was wiring up the firezog line out mod that lk turned me onto i came up with a question. it's obvious that when the speaker is unplugged the resistor in line there subs for the speaker impedance. but what happens to the overall impedance if you wanted to use the amp with both the speaker plugged in and the line out plugged into a house pa or another amp? there's a sentence at the bottom of the directions that says "a reactive load may also be plugged into the speaker jack, if desired." i'm not at all sure what a reactive load is but does that mean it's safe to use both at the same time?

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as i was wiring up the firezog line out mod that lk turned me onto i came up with a question.  it's obvious that when the speaker is unplugged the resistor in line there subs for the speaker impedance.  but what happens to the overall impedance if you wanted to use the amp with both the speaker plugged in and the line out plugged into a house pa or another amp?  there's a sentence at the bottom of the directions that says "a reactive load may also be plugged into the speaker jack, if desired."  i'm not at all sure what a reactive load is but does that mean it's safe to use both at the same time?

I'm not entirely sure what you are asking.. but a reactive load would be a dummy coil as opposed to a strictly resistive load, like a resistor based attenuator or dummy load. Weber Speakers sells all kinds of attenuator and speaker load products.. the active loads are basically speakers without cones. Provides the most natural load for your output amp, and to it.. feels just like a speaker.

Generally speaking, a line out shouldn't have anything to do with the speaker output.. as the lineout is unamplified and the speaker output is. The line out should exit the amps circuitry just before entering the power amp section.

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http://home.cfl.rr.com/dbhammond/Firezog.gif

sorry, should have included the link. ok, i see what they mean about the reactive load but with this mod the line out appears to exit at the same place the speaker jack does. to clarify the question: can you use both the line out and the speaker at the same time without danger to the amp?

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Oh i see.. it's just pulling the power down out of the amps output to a line level.. interesting. The weber guy I mentioned has calculators on his site for figuring resistor ratings to match different output ohms and wattages. I used his info to build an attenuator for my tube amp.. I've seen attenuators with a line out option, looks like the same concept.

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BTW, if you're using this for anything with appreciably higher power than the Firefly, I'd recommend bumping up the resistor power ratings to match.

actually this is going into the little champ i'm building. i assumed that since the speakers are only a 4ohm load that i should drop the 10ohm/5w down to a 5ohm/5w. is that not right?

The weber guy I mentioned has calculators on his site for figuring resistor ratings

thanks, i'll check that out this evening.

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