Expert: Cleggsan - 10/8/2008

Question
QUESTION: can you bridge a Sansui Home Audio Power Amp B-3000? Would like to put the 2x120 watt stereo ouputs into one x 240 mono? I can't see any provisions for this on the rear of unit.

ANSWER: On this amp the bridging would be done from the back panel.  Usually it requires a switch somewhere.

If you know how to do it you can convert it for mono use by adding an inverter on one channel and connecting the speaker between the two positive terminals at the output.  Do you know what I am talking about?

(NOTE: The bridging conversion does not apply to amplifier circuits that have capacitor coupling at the output - in most cases.)

PS: I just found a photo of the back side of this amp and do not see any evidence of bridging, but this is not necessarily conclusive.


C



---------- FOLLOW-UP ----------

QUESTION: I guess I don't see how a battery  D/C voltage invertor is going to bridge the audio output on a A/C music power amp. Just can't picture it in my mind. Thanks for your reply and I'll keep thinking on it awhile.
Me thinks we got our wires crossed.
Thanks
Oz

ANSWER: No, no, no. Sorry.  Not a battery, power inverter, but an audio signal inverter.

To bridge an amplifier one channel is driven with an out-of-phase signal such that when one channel of the stereo amp is going positive with the music signal the other channel is going negative.  That produces twice the voltage at the output terminals for the speaker.

Amps that have bridge connections built in have this extra signal inverter built in and when the amp is switched over to bridge it puts the signal inverter into one channel.....   Got it?  

A bridging configuration only works well with amplifiers that have direct coupled output stages.

See the middle of this page which shows the concept for a bridged amplifier:

http://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers

Hope this clears it up.

c


---------- FOLLOW-UP ----------

QUESTION: i got you now...
I need an audio power invertor,
and follow that schematic you sent the link for thanks for the extra input!!
Crystal clear understanding now.
thanks much

Answer
By the way, another way to input a stereo amplifier so that it can be bridged at the output is to use a center tapped audio transformer on the input.  The center tap is grounded and one side drives one channel and the other side drives the other channel.  The input signal drives the primary side of the transformer.  The speaker is then connected across the two plus terminals at the output...   

Good luck,
C