Reversing speaker selector switch. Need advice.

maurycy · 18th January 2008, 02:24 AM

This is a follow up to my previous post . Basically I am trying to build a small switch box that will allow me to connect one speaker pair to two audio sources (my Denon receiver and my newly built gainclone amp). Finally I have found a speaker selector switch on Ebay for $2.99 that has no protection built in. It is just a rotary switch that connects wires. I have opened the case and peeked inside to check the wiring. My concern is that the negative speaker wire is not connected thru the switch. It just splits from input and goes to both speaker outputs. Would that cause any problems if I simply reverse the switch?

Thanks.

Iain McNeill · 18th January 2008, 02:50 AM

As long as your amps aren't bridged you should be OK. You do, however, have to make sure that all the ground returns are commoned and you're only switching the actual amplifier outputs. If you get the polarity wrong and common all the amp outputs and try to switch the ground returns, bad things could happen.

maurycy · 18th January 2008, 10:51 PM

Iain, could you enlighten me what a bridged amplifier is? I am noob when it comes to electronics.

Thanks.

Iain McNeill · 21st January 2008, 02:47 AM

A way of getting more power is two use two amplifiers each driving one terminal of the speaker but feeding the amplifiers in anti-phase. You get a doubling of the voltage across the speaker. This is called bridging an output (or a pair of amps)

Where this is important is if your switch needs one wire to be commoned between the amplifiers for each speaker channel. If the commoned wire is ground on both ampifiers then everythings OK you connect ground to ground. However, if one (or both) of the amplifiers is bridged i.e driving both output terminals, then when you common the two amp wires in the switch, you'll short out the bridged amp channel to the ground of the other amp.

maurycy · 21st January 2008, 02:31 PM

Thanks for the explanation.

As far as I know, the gainclone amp that I have built is not a bridged amp. It is just a stereo non-inverting amplifier. But how can I check if my Denon DRA-295 is bridged or not?

18th January 2008, 02:24 AM	#1
maurycy diyAudio Member Join Date: Dec 2005 Location: NJ	Reversing speaker selector switch. Need advice. This is a follow up to my previous post . Basically I am trying to build a small switch box that will allow me to connect one speaker pair to two audio sources (my Denon receiver and my newly built gainclone amp). Finally I have found a speaker selector switch on Ebay for $2.99 that has no protection built in. It is just a rotary switch that connects wires. I have opened the case and peeked inside to check the wiring. My concern is that the negative speaker wire is not connected thru the switch. It just splits from input and goes to both speaker outputs. Would that cause any problems if I simply reverse the switch? Thanks.

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18th January 2008, 02:50 AM	#2
Iain McNeill diyAudio Moderator Join Date: Oct 2007 Location: Santa Cruz, California	As long as your amps aren't bridged you should be OK. You do, however, have to make sure that all the ground returns are commoned and you're only switching the actual amplifier outputs. If you get the polarity wrong and common all the amp outputs and try to switch the ground returns, bad things could happen.

18th January 2008, 10:51 PM	#3
maurycy diyAudio Member Join Date: Dec 2005 Location: NJ	Iain, could you enlighten me what a bridged amplifier is? I am noob when it comes to electronics. Thanks.

21st January 2008, 02:47 AM	#4
Iain McNeill diyAudio Moderator Join Date: Oct 2007 Location: Santa Cruz, California	A way of getting more power is two use two amplifiers each driving one terminal of the speaker but feeding the amplifiers in anti-phase. You get a doubling of the voltage across the speaker. This is called bridging an output (or a pair of amps) Where this is important is if your switch needs one wire to be commoned between the amplifiers for each speaker channel. If the commoned wire is ground on both ampifiers then everythings OK you connect ground to ground. However, if one (or both) of the amplifiers is bridged i.e driving both output terminals, then when you common the two amp wires in the switch, you'll short out the bridged amp channel to the ground of the other amp.

21st January 2008, 02:31 PM	#5
maurycy diyAudio Member Join Date: Dec 2005 Location: NJ	Thanks for the explanation. As far as I know, the gainclone amp that I have built is not a bridged amp. It is just a stereo non-inverting amplifier. But how can I check if my Denon DRA-295 is bridged or not?

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