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[Ivan Beaver]

I have searched, but cannot seem to find an answer.

When you bridge a QSC PL380, does the GAIN (Not concerned with the POWER capability) of the amp go up 6dB (as most do), or is there a gain reduction in the setting that keeps the overall gain of the bridged configuration the same as a single channel, but allows for 6dB greater output-due to the bridging?

Any help would be appreciated.

Thanks

[John Roberts {JR}]

Since they label a specific voltage gain on the switches, it "should" compensate to deliver the same specified voltage gain in bridge mode or not.

"Should" does not mean does... you know the drill ask QSC or measure one.

JR

[Ivan Beaver]

Since they label a specific voltage gain on the switches, it "should" compensate to deliver the same specified voltage gain in bridge mode or not.

"Should" does not mean does... you know the drill ask QSC or measure one.

JR

Of course if I had one I would measure it.  That is always the best way.

Part of the question is obviously looking for an answer, but the other "hidden part", is to help educate people who may not think about the 6dB of added gain (by doubling the output voltage) when you bridge an amp.

I made a mistake years ago (last century), at my first rap show.  Outside at a football stadium.

I decided at the last minute to bridge my Crown MA2400s into my double 18 subs to get "more headroom".

The limiters on my BSS360s were set for normal operation.

I "forgot" about the added gain when bridging, and blew up all my subs.  Yes, 4 times the power and sine waves will do that

Luckily I had a whole pile of 15" drivers for lows and made it through the show with compliments that it was better than the last one they had.

[Mark Wilkinson]

Hi Ivan, bridge mode puts out +6......no automatic compensation

[Ivan Beaver]

Hi Ivan, bridge mode puts out +6......no automatic compensation

Thanks.  I know most amps will have the 6dB of gain.  I can't remember the ones, but I know some will drop the level 6dB to keep it the same.

But that takes more circuitry than a simple switch.

And the +6dB makes is louder-so that is a good thing-right??   

[John Roberts {JR}]

Thanks.  I know most amps will have the 6dB of gain.  I can't remember the ones, but I know some will drop the level 6dB to keep it the same.

But that takes more circuitry than a simple switch.

And the +6dB makes is louder-so that is a good thing-right??   

Yes it could require another pole on the bridge switch if switched physically. Not only must you change one input to get an inverted version of the other, but to keep voltage gain correct you need to attenuate both. When routing signals around inside power amps there is strong motivation to keep it simple and straightforward.

A fair compromise in my opinion would be to list both voltage gains on the sensitivity switch labels showing the bridged voltage gain also. The larger sin is not how you handle the bridged gain, but to force the customer to guess.

JR

[Kemper Watson]

Of course if I had one I would measure it.  That is always the best way.

Part of the question is obviously looking for an answer, but the other "hidden part", is to help educate people who may not think about the 6dB of added gain (by doubling the output voltage) when you bridge an amp.

I made a mistake years ago (last century), at my first rap show.  Outside at a football stadium.

I decided at the last minute to bridge my Crown MA2400s into my double 18 subs to get "more headroom".



The limiters on my BSS360s were set for normal operation.

I "forgot" about the added gain when bridging, and blew up all my subs.  Yes, 4 times the power and sine waves will do that

Luckily I had a whole pile of 15" drivers for lows and made it through the show with compliments that it was better than the last one they had.

Need to borrow one??

[Ivan Beaver]

Need to borrow one??

You could always do a real quick test for me.

Simply put a sine wave into channel 1 (turn Channel 2 all the way down) in stereo operation

Measure the voltage across the output terminals of channel 1.  It doesn't matter what it is-10-20 30Volts etc.  Just make sure the amp is not clipping.

Now-without changing anything level, put the amp into bridge (it is always a good idea to turn the amp off-flip the switch-then turn it back on).

No measure across the bridge outputs (the red terminals).

If the voltage doubles, there is no gain compensation.  If it stays the same, there is gain compensation

[Ben Mehlman]

You could always do a real quick test for me.

Simply put a sine wave into channel 1 (turn Channel 2 all the way down) in stereo operation

Measure the voltage across the output terminals of channel 1.  It doesn't matter what it is-10-20 30Volts etc.  Just make sure the amp is not clipping.

Now-without changing anything level, put the amp into bridge (it is always a good idea to turn the amp off-flip the switch-then turn it back on).

No measure across the bridge outputs (the red terminals).

If the voltage doubles, there is no gain compensation.  If it stays the same, there is gain compensation

I think it would be.. if it doesn't change, there's no compensation.  If it goes down, then there is.

[Mac Kerr]

I think it would be.. if it doesn't change, there's no compensation.  If it goes down, then there is.

Why would that be, since you would be measuring across the hots of 2 identical but different polarity terminals. The voltage swing should be twice as much as across only 1ch.

Mac

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