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renfrow 21st November 2006 08:32 PM

How do you tell if an amp is bridgeable?
Ok, what I'm actually asking about is a receiver. I have boatloads of jazz and classical music from the 50's and earlier that is mono. What I'd like to do is build a single speaker just for listening to this, and hook it up to the B outputs of a receiver. I'd prefer to not to have to build an amp (sorry :cannotbe: ) just for this, though I'm willing to build a speaker ;).


mikee55 21st November 2006 09:58 PM

Bridge circuit needed
Hi renfrow,
Why don't you just listen in mono from the stereo you have? Mono comes out in mono on a stereo.
Briding an amp is adding distortion. When a class a/b amp is used as most are, you have a crossover distortion, yeah? If you bridge you'll get twice the crossover distortion, and supposedly more power avaiable to a speaker. Why don't you use a splitter and split the mono to Left and Right inputs or better still use a PC audio editor and create a synthesized stereo. Apparently, if you put a mono signal into a stereo reverb, technicaly the output is stereo. I think if you try and add just a slight echo and try and create the ambience of an average sized studio (or hall if a live recording), this wouldn't too far from mono rather than pan and expand(which could create a hole in the soundstage), and would be an interesting project. Am I to assume your recordings are vynil? Archiveing them digitaly would allow you to preserve the originals. I'm no expert, but going the digital route with an editor such as Wavelab or Soundforge, (there is Freeware editors out there on the www too), and if you had a decent soundcard and cd writer, you wouldn't go far wrong.

What do you think?

Cheers Mike:)

K-amps 22nd November 2006 11:01 AM

Hello Tom:

Let me try and answer the question without being a prude :D .

Your amp is bridgeable if it's outputs are grounded one one side. i.e. the "black" speaker posts have zero volts while driving the load and the "red" posts provide the voltage/current.

It both sides are hot i.e. drving the load, then it is already bridged and cannot be bridged again.

As far as how you bridge it is another story...

sreten 22nd November 2006 11:46 AM


Some of us prefer the "floating" presentation of mono material over
a stereo pair of speakers but if you want one speaker fair enough.

Also note addding a mono button to your turntable (if the amplifier
doesn't have one) will significantly reduce apparent surface noise.

If you add a mono button simply use one speaker off one B-channel,
the other channel you can put a dummy load on, say a 50R 3W resistor.


jackinnj 22nd November 2006 12:09 PM

Re: Bridge circuit needed

Originally posted by mikee55

Briding an amp is adding distortion. When a class a/b amp is used as most are, you have a crossover distortion, yeah?

Do you want to demonstrate that empirically?

mikee55 22nd November 2006 09:21 PM


jackinnj 22nd November 2006 09:40 PM

Here's what I found (empirically) -- both amps were run from the same power supply with the identical signal source.

K-amps 23rd November 2006 12:32 AM

As far as non-empirical evidence goes, I have always liked the less grainy and less fatiguing sound of bridged amps.

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