Is it possible to bridge two subwoofer plate amps between circuit boards?? - diyAudio
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Old 15th February 2014, 09:16 AM   #1
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Default Is it possible to bridge two subwoofer plate amps between circuit boards??

I have a pair of NHT closeout sale Foster sub amps. There are instructions for bridging these amps with external connections requiring very careful manual adjustment of controls on both amps.

I wonder if it's not possible to bridge the amplifier section of one amp to another, bypassing the controls and merely bridging the amplifier section. One amp being the "slave" with non functioning volume control and the the other's volume control being the main.
This is the schematic. Is it possible to point out where I might solder such a jumper/bridge between the two circuit boards?

Last edited by peace brainerd; 15th February 2014 at 09:19 AM.
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Old 19th February 2014, 09:32 AM   #2
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For the apparent embarrassment of wealth of genius in this forum section I thought this would be a slam dunk.

Can someone at least disabuse me of the idea?
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Old 19th February 2014, 09:53 AM   #3
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There is an article on Rod Elliot's ESP site, called something like simple bridging adapter, that shows what you need to do. Basically you need to configure the slave amp as a unity gain inverting amp and run it from the output of the master.
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Old 19th February 2014, 10:22 AM   #4
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Maybe guys are suggesting somehow, you perhaps try the subwoofer forum.

The main consideration when bridging amplifiers is at what risk to the power amplifiers? Sales guys don't care too much about what Joe Public does after goods are sold unless they have to cover accidental damage under warranty. All they need to do is say yes, you can bridge it because that's what most guys ask - it does seem like free power, no?

According to the schematic, you only have a single pair of TO3P output transistors running on 50V rails. This is not suited to bridging since you effectively halve the load impedance from say 8 to 4 ohms for each amplifier when you try to get full available power. If you start with a 4 ohm speaker, the bridged amplifiers effectively "see" only 2 ohms and so on. So you won't achieve much, other than put the amplifiers in current limiting protection mode, assuming that works properly.

Better to simply run 2 subwoofer systems in parallel, with their own speakers - giving full rated 8 ohm power within rated specs. when using typical 8 ohm sub. speakers.
No extra fuss or risk then.

Last edited by Ian Finch; 19th February 2014 at 10:28 AM.
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