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Old 23rd March 2003, 11:08 PM   #1
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Question bridging amps?

i would appreciate any links as i have searched but cant find any info online...


i need some solid facts not opinion and vagueness hehe

i have a 100watt amp @ 4ohms and am thinking of buying another module to bridge it with.
>how many watts will i have at 4ohms,and at 8hms(as i may have to buy an efficient 8ohm speaker)

all i know is that i will have half as much power at 8ohms than 4.



bridging home audio sub amps.


thanks alot! ..

btw. to post in the other parts of diyaudio do u have to subscribe to it first?
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Old 23rd March 2003, 11:14 PM   #2
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Default check this out...

Check out this link:
http://sound.westhost.com/project14.htm

the latter part of the article explain bridging,
there is also another bridging adapter on this great site

Pete McK
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Old 23rd March 2003, 11:37 PM   #3
haldor is offline haldor  United States
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Hi Mike,

Rod Elliot has a discussion about Bridging amps on his website at:

http://sound.westhost.com/bridging.htm

Bridging is a way of taking two mono amps (or both sides of a stereo amp and using them to power one speaker. How it works is you need a signal inverter (can make one pretty easy with an op-am in an inverting configuration at a gain of 1). The original signal is fed to one amp and the inverted signal is fed to the second amp.

The speaker is connected across the two hot outputs of the amps (the ground speaker connections are not used). What happens when you do this is the speaker sees double the voltage signal from the amp (one terminal is going + while the other terminal is going -). This effectively makes the speaker look to the amp like it is half it's original impedance. End result is you get the same power that would normally be delivered into each channel with a 4 ohm load only it's fed into a single 8 ohm load. This is normally what you want for a subwoofer.

You do need to watch out that your amp is able to handle the strain of doing this. For example, connecting a 4 ohm speaker to a bridged amp demands the same current as connecting a pair of 2 ohm speakers to the amp (one on each output in stereo mode). Not very many home stereo amps are able to handle loads below 4 ohm's, so when used bridged they should be limited to an 8 ohm load. If you amp is not able to handle a 4 ohm load then it is not a good candidate for bridging.

Now you make ask yourself, self, why do people do this? Three reasons:

First: Just about all car amps are used in bridged mode. This is so you can get a much power as possible from the 12 VDC battery supply (double what you would otherwise be able to get). This is the reason why most "hi-power" car receivers are often limited to about 24W per channel (unless they are lying about how much power they output).

Second: Most amps are stereo (2 channel). Bridging permits you to take a stereo 100W amp and end up with a 200W mono amp.

Third: Most amps will deliver much more power into a 4 ohm load than they do into an 8 ohm load. If you have an 8 ohm sub then you are not getting close to the full power out of the amp. By running it in bridged mode you get as much amp into that single 8 ohm speaker as the amp would deliver into two 4 ohm speakers.

Phil
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Old 23rd March 2003, 11:39 PM   #4
haldor is offline haldor  United States
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Location: Columbus, Ohio
Default Re: check this out...

Quote:
Originally posted by PeteMcK
Check out this link:
http://sound.westhost.com/project14.htm

the latter part of the article explain bridging,
there is also another bridging adapter on this great site

Pete McK
Pete jumped in with his post while I was composing my usual novel. I do recommend anyone interested in audio design to read through Rod's website, lots of usefull info.

Phil
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Old 24th March 2003, 03:08 AM   #5
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Talking amp

Thanks very much guys!
the theory makes sense.


>>>This effectively makes the speaker look to the amp like it is >>>half it's original impedance. End result is you get the same >>>power that would normally be delivered into each channel >>>with a 4 ohm load only it's fed into a single 8 ohm load.

so my 8ohm speaker appears to be 4ohms when bridged...

and my 2x100watt @ 4ohm amps will give 200watts into this speaker.

am i understand ing it correcly ?

(some one told me this,but i didnt beleive him i thought id get 200watt at 4ohms and 100watt at 8ohms hehe)




if so,that is very good for me!

i just need to buy a toroid for it,

28/28V and 5.3A is that enough for both 100watt modules
(they reccomend 28/28 2.2A (which is probaby abit under rated))
i mean,,
i actualy only need 150watts 200 is heaps :-D

i could almost run a shiva off that much.but its 4ohm and those amps ,,im not sure if they would like 2ohms! :-D (and buying yet another more high power transformer lol)

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