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driving old sub amp with pre-amp out instead of speaker out
driving old sub amp with pre-amp out instead of speaker out
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Old 2nd July 2020, 10:07 PM   #11
Perplexed1ne is offline Perplexed1ne
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driving old sub amp with pre-amp out instead of speaker out
That’s helpful. From this link I have leaned what a voltage divider is and that:

If learning Ohm's law was like being introduced to the ABC's, learning about voltage dividers would be like learning how to spell cat.

LOL

Many thanks
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Old 3rd July 2020, 09:07 AM   #12
ubergeeknz is offline ubergeeknz  New Zealand
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I've just been watching a couple of videos which really cover this stuff well. Check this channel out:

YouTube
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Old 3rd July 2020, 11:58 AM   #13
bentoronto is offline bentoronto  Canada
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Location: Toronto and Delray Beach, FL
driving old sub amp with pre-amp out instead of speaker out
Quote:
Originally Posted by ubergeeknz View Post
Here's an example, probably fairly typical. From a JBL sub plate amp.Attachment 857408

If I read it right, the speaker-cable input has a load resistor of 100 Ohms. Some pre-amps might play OK into that load albeit with a low voltage signal but doesn't sound really acceptable.

But the speaker-cable input is reduced to 10% (compared to the pre-amp jack) before continuing on its path in the amp. Which may mean that your amp (which expects a speaker-cable signal) is expecting a signal 10X what a pre-amp would typically supply. Again, might work OK even with that head-wind, but doesn't sound really sensible.

Sticking with the schematic, if you open the amp, you might find something like that 100kOhm resister or some voltage divider being used to cut down the speaker-cable input before the first amplification stage. A simple matter to disable the voltage division.

You are also using a coax output from your pre-amp into unshielded in the amp. For most pre-amps, it shouldn't introduce too much noise. But take care about ground connections.

BTW, "10X" is like 20dB voltage increase which is like what the amp portion of an amplifier would typically provide. So it makes sense to see that inside the pictured schematic.

B.
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Last edited by bentoronto; 3rd July 2020 at 12:05 PM.
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Old 3rd July 2020, 12:28 PM   #14
ubergeeknz is offline ubergeeknz  New Zealand
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Fair to say, depending on the exact design of your particular subwoofer amp, you may be able to change a few components and adapt it for your intended use, but it's unlikely to work well without modification.

May be an interesting challenge if you want to figure out how this all works driving old sub amp with pre-amp out instead of speaker out
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