Threshold 400A

[Airedale]

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 !

 

[Nelson Pass]

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.

 

[Airedale]

Thanks for the info Nelson !!

 

[Eric M]

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

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.

 

[Zen Mod]

any generic unbal to bal converter circuit will do the job

simplest will be 10K:10K+10K xformer

 

[Eric M]

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

any generic unbal to bal converter circuit will do the job

simplest will be 10K:10K+10K xformer

 

[Zen Mod]

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

 

[Eric M]

Thank you for that info. and thanks for the help!

Eric

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

 

[R-K Rønningstad]

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.

 

[Zen Mod]

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

 

[Eric M]

Would the same set up work for the Threshold Stasis 3 to run bridged?

Eric M.

 

[Zen Mod]

yup

 

[R-K Rønningstad]

It should work for all amplifiers. But if the amplifier is inverting you would like to figure out if you would do a different coupling at the XLR to 2xRCA or at the loudspeaker.

 

[Eric M]

Great!

Thanks again.