Crown 460 CSL Mono Bridge Problem - diyAudio
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Old 29th December 2009, 04:16 PM   #1
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Question Crown 460 CSL Mono Bridge Problem

Hi.

I just bought a used Crown 460 CSL Amplifier.
Both channels work great in stereo mode but i'm having a problem with mono bridge mode.
I've been searching all over the internet for information about this and couldn't find much information.
I've been through the service manual many times.

My problem is that when the amplifier is set to operate in mono bridge, i can barely hear the sound coming from my speaker (turning the gain knob doesn't help).
I am using an unbalanced 1/4" jack connection for the input (channel 1).
Outputs are going from both Red connections from Channel 1 & 2.
Switch is set to Mono Bridge.

When both channels are driven independantly in stereo mode, everything is great, sound comes out loud and clear.
Though, since i'm trying to drive a single 400w 18" sub, this use is impractical and i require the mono bridge operation.

Since i do not have much experience repairing amplifiers, i am a bit stuck.

I was wondering if anyone might have suggestions of things i could try so i can diagnose the problem and maybe find a solution ?
Anything will be much appreciated.

Thanks !
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Old 29th December 2009, 06:00 PM   #2
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By the way, these are the schematics for the amplifier :

http://www.crownaudio.com/pdf/legacy...-j0694-0_c.pdf
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Old 29th December 2009, 10:02 PM   #3
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I would assume that the amp must be running in parallel mono instead of bridge mono.
In Parallel Mono both outputs are the same phase and voltage.
The Speaker wires are connected -Ve to the ground and +Ve wire is connected to both positive outputs. This is suitable for a 2 to 4 Ohm Load.

In Bridge mono the outputs are out of phase with each other, and the speaker wires are connected individually to the positive connections.
This works well for 8 to 16 ohm speakers.

What is the speaker impedance you are trying to drive?
If you connect the speaker to the individual channel binding posts are both channels working (in the bridge switch position)?
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Old 30th December 2009, 07:12 PM   #4
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The impedance of the sub is 8 Ohm.
Yes, both channels are working independantly when the switch is in the "Mono Bridge" position.
While opening and looking inside the amp, i noticed it has been fiddled with by the previous owner.
I will call him and see if he knows anything about this issue.

Your hypothesis about Parallel Mono makes alot of sense.

Though, I am really not sure how i would go about fixing that.

Last edited by janvitos; 30th December 2009 at 07:23 PM.
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Old 30th December 2009, 09:44 PM   #5
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Just to let you know, while the amp is set to "Mono Bridge", I tried switching my input between both input 1 and 2.
I get the same low sound from both channels while my output is plugged as bridged (both red terminals).
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Old 31st December 2009, 01:17 AM   #6
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Parallel mono does not work the same as bridged mode. parallel mode simply is a way to connect one input to both channels, you connect the speakers to the red/black binding post's as you would in stereo. again this simply connects both inputs together.

BRIDGED mode inverts the polarity of one channel so you can connect the speaker across the red post's. If you have no, or little sound in this mode. I would suspect that the switch is bad/dirty or broken. and one channel is not being inverted. In Bridged mode you are hearing the difference signal between channels. if the signal of both channels is the same, you get no sound.
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Old 31st December 2009, 03:08 AM   #7
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So let's say the switch is defective, or somewhere else in the amplifier, the signal is not being phased out properly.
Assuming the bridge module might be broken, since i am getting sound in both channels, might there be a way to manually bridge the amplifier ?
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Old 1st January 2010, 04:28 PM   #8
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Quote:
Originally Posted by janvitos View Post
So let's say the switch is defective, or somewhere else in the amplifier, the signal is not being phased out properly.
Assuming the bridge module might be broken, since i am getting sound in both channels, might there be a way to manually bridge the amplifier ?
A quick fix might be to make a custom lead using the amplifier balanced inputs
Link the inputs together but change the polartity on XLR pins 2 & 3.
Run the amp in stereo mode setting - You would need to adjust both volume controls together. This should phase the outputs, and allow you to run the speaker bridged across the positive terminals, without changing the amplifier internals.
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Old 27th February 2015, 12:07 PM   #9
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I've had this same issue using a direct connection to the speaker, however in stereo mode with chinch connectores, the sound was louder.

I've wired the speaker directly to the amp in parallel mono mode 4 Ohm and the speaker imploded & started smoking up fumes immediately.
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