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Old 16th January 2005, 08:52 AM   #1
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Default Threshold 400A

I have a 400A but have long lost the manual - LOL. Can anyone tell me if this Amp can be easily bridged for a mono application ? If so can you tell me how to bridge it ? Will the unit still operate as Class A in Mono mode ? Thanks !
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Old 17th January 2005, 10:26 PM   #2
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If you have a source with 2 phases (+/-) also known
as a balanced source, you can feed each into an input
and operate the amplifier bridged. It will leave Class A
at some point short of 400 watts into 8, but I don't recall
offhand what that point might be.

If you don't have a balanced signal source, it is possible to
tap the output of one channel into the (-) input of the
differential pair of the other channel, but this gets a little
technical.
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Old 17th January 2005, 11:57 PM   #3
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Thanks for the info Nelson !!
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Old 19th December 2015, 03:59 PM   #4
Eric M is offline Eric M  United States
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I would love to use one of my 400a for the center channel in my surround system. But, it would be an unbalanced source. Nelson, could you post the details for bridging this amp for unbalanced inputs? Or, do you think this is just too much of a task for this particular amplifier?

Thank you,

Eric


Quote:
Originally Posted by Nelson Pass View Post
If you have a source with 2 phases (+/-) also known
as a balanced source, you can feed each into an input
and operate the amplifier bridged. It will leave Class A
at some point short of 400 watts into 8, but I don't recall
offhand what that point might be.

If you don't have a balanced signal source, it is possible to
tap the output of one channel into the (-) input of the
differential pair of the other channel, but this gets a little
technical.
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Old 19th December 2015, 05:15 PM   #5
Zen Mod is offline Zen Mod  Serbia
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any generic unbal to bal converter circuit will do the job

simplest will be 10K:10K+10K xformer
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Old 19th December 2015, 07:37 PM   #6
Eric M is offline Eric M  United States
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Thanks,

Would something like this do the trick?

Rolls DB24 - Stereo Direct Interface DB24 B&H Photo Video

I'm confused how I would make the connection from the XLR balanced output of the converter to the RCA input jacks of the 400a to make it operate in bridged mode?

I'm assuming I'd use the positive speaker posts of the left and right channel for my single speaker connection. Any idea how I'd determine which is the negative when operated like this?

Are there any internal modifications I will need to do for this? I did a Hafler 220 once and remember having to switch wires around on the circuit boards.

Thanks for the help.

Eric




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Originally Posted by Zen Mod View Post
any generic unbal to bal converter circuit will do the job

simplest will be 10K:10K+10K xformer
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Old 20th December 2015, 08:08 AM   #7
Zen Mod is offline Zen Mod  Serbia
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XLR balanced output of the converter to the RCA input jacks of the 400a :

XLR pin 1 to both RCA gnd

XLR pin 2 to right RCA hot

XLR pin 3 to left RCA hot

speaker leads to right and left output hots (same as with DH220)

I believe 400A is not flipping phase , but to be sure - make simple phase test (mono) , every test CD is having that track
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Old 7th January 2016, 09:06 PM   #8
Eric M is offline Eric M  United States
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Thank you for that info. and thanks for the help!

Eric



Quote:
Originally Posted by Zen Mod View Post
XLR balanced output of the converter to the RCA input jacks of the 400a :

XLR pin 1 to both RCA gnd

XLR pin 2 to right RCA hot

XLR pin 3 to left RCA hot

speaker leads to right and left output hots (same as with DH220)

I believe 400A is not flipping phase , but to be sure - make simple phase test (mono) , every test CD is having that track
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Old 7th January 2016, 11:48 PM   #9
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Quote:
Originally Posted by Zen Mod View Post
XLR balanced output of the converter to the RCA input jacks of the 400a :

XLR pin 1 to both RCA gnd

XLR pin 2 to right RCA hot

XLR pin 3 to left RCA hot

speaker leads to right and left output hots (same as with DH220)

I believe 400A is not flipping phase , but to be sure - make simple phase test (mono) , every test CD is having that track
Absolute phase preserved on my 400A. Mighty Zen is right as always.
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Old 7th January 2016, 11:58 PM   #10
Zen Mod is offline Zen Mod  Serbia
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as I said before ..... when I'm writing rubbish , that's Mighty Moi ;

when I'm right , that's Pa in fact , using my account

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