Can any amplifier be bridged?

Surtsey

Member
2019-09-21 4:51 pm
I embark on weird projects to keep me out of trouble. Recently I acquired a microsystem - JVC UX-J55v. It's knackered, neither the CD or cassette player works but one aspect of the specs intrigued me: 60w + 60w RMS.

I want to use the PSU and amplifier board to power my active subwoofer project. Is this even possible? I can design the sub to use 2 x 5" drivers but I'd prefer to drive a single 6.5" in mono.

Can I get a little help?
 

rayma

Member
2011-04-29 8:37 pm
You need a unity gain inverting op amp circuit on one of the inputs, and then you can use a regular stereo amp
(the negative output terminal must be grounded on each channel) as a mono bridged amp.
Make sure the speaker's impedance is at least twice the minimum impedance rating of either channel.
If one channel of your amp can drive 6R, then the woofer should be 12R or higher.
 
Last edited:

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Surtsey,
I wouldn't bridge that amplifier for one of two reasons.

1.) It may already be in bridge mode for each channel, so bridging it further buys you nothing.
2.) Bridging the amplifier will make an 8 ohm load look like a 4 ohm load to the amplifier. It would probably be beyond it's safety margins leading to amplifier failure.

Use it in straight stereo mode for the sub. Use only one channel if you can't use a pair of 6 1/2" speakers.

Best, Chris
 
I embark on weird projects to keep me out of trouble. Recently I acquired a microsystem - JVC UX-J55v. It's knackered, neither the CD or cassette player works but one aspect of the specs intrigued me: 60w + 60w RMS.

I want to use the PSU and amplifier board to power my active subwoofer project. Is this even possible? I can design the sub to use 2 x 5" drivers but I'd prefer to drive a single 6.5" in mono.

Can I get a little help?

Any stereo amplifier that is not already bridged can be bridged. The real question is the practicality of it. As others have pointed out you have to be careful with loading, using higher impedance speakers and avoiding complex crossovers. There is also some consideration to be given to the power supply, since some, especially in entry level equipment, will be over-taxed by the constant currents of BTL operation.

To bridge an amp you need a phase splitter. Although easily built, these can cost you the price of a new Class D board to use in your subwoofers. I would suggest some shopping around before you do this.
 
Most STEREO amplifier can usally be bridged, however the total load must be 2x rated load. If min load is 4 ohms the total must be 8 ohms or greater. This mod changes the way each amplifier is driving the total load. Now each amplifier drives ½ (or 4 ohms) of the total load.

One of the amplifiers must be modified to become a unity gain inverting amplifier.

Short the input signal of the undriven amplifier and add a new resistor to the feedback. If the feedback resistor is say 47.5k (output to summing junction) then add a 47.5k resistor to the output of the driven amplifier.

This mod makes the slave amplifier a unity gain inverting amplifier.

Duke
 
One of the amplifiers must be modified to become a unity gain inverting amplifier.

Short the input signal of the undriven amplifier and add a new resistor to the feedback. If the feedback resistor is say 47.5k (output to summing junction) then add a 47.5k resistor to the output of the driven amplifier.

This mod makes the slave amplifier a unity gain inverting amplifier.

Simplest Ever Bridging Adapter for Amplifiers
 

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