Plate amp speaker input impedance and running speakers and sub in parallel - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 4 Old 06-29-2012, 12:53 PM - Thread Starter
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Not the normal type of question for this forum, but I knew that the people that know the most about plate amps hang out here smile.gif

Two questions:

1) What is the impedance of the speaker level inputs on a plate amp? Specifically the kind that doesn't have any pass through for speaker level output?
2) Is it reasonable to run a pair of 8 ohm speakers in parallel with the sub--connected by the speaker level inputs--of a 2 channel amp?

Sorry for the oddball question, but here's the situation. I have an old HK 35 AVR that all the DSP burned out. Only the front L/R are left, and it still sounds great with a pair of speakers in a budget computer 2.0 setup. The HK can run 4 ohms no problem.

I'd like to hook a sub up to it. But since the sub line out is gone on the receiver and there is on the L/R out, that limits my options to budget subs that have speaker inputs and outputs, which is very limiting on the choices. On the other hand, if I can hook a sub with speaker level inputs in parallel with the speakers, that opens up my options a lot.

I've seen this kind of problem pop up in other budget 2.1 setups.

Thanks!

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post #2 of 4 Old 06-29-2012, 02:43 PM
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Yes, it is reasonable. It is typically a high-resistance, voltage divider network. Whether it has a pass-through is a matter of convenience, as the pass-throughs are usually equipped with a simple 6dB hp filter. I just looked at a Klipsch BASH amp schematic. It looks like the high level inputs will present roughly a 220ohm load. In the electronics world, any parallel, resistive load that is 10x higher can safely be ignored. Hope this helps.

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post #3 of 4 Old 06-29-2012, 02:52 PM - Thread Starter
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Cool. I was wondering if it would be that high. I wonder if the plate amps on all commercial subs are likely that high?

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post #4 of 4 Old 06-29-2012, 06:54 PM
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I'd guess so, since most are expected to be run with front mains as well. I wouldn't think they'd include high-level inputs, if they didn't make sure it would not be a significant load on your amp or receiver.

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