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Old 7th May 2008, 10:05 PM   #1
gupsta is offline gupsta  United Kingdom
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Default balanced signal

Hi

I should be getting a bk electronics mfx600 soon, which has balanced outputs. xlr i think. Don't know alot about balanced

signals, but my understanding based on reading around is that there are two signals (+/-) and earth. And when they are

recombined the -ve is subtracted from the +ve giving twice the output signal strength (x-(-x) =2x).

Anyway the bit i'm lost on is how the signal is supposed to get recombined before going into the passive crossover/speaker cone.

I'm guessing i'll need to add something inside the speaker cabinet to do the job but don't know what. Any ideas ?

Thanks
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Old 8th May 2008, 12:50 AM   #2
gni is offline gni  United States
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A balanced output on a power amplifier is different than
a balanced input signal. . . The inputs of a balanced amplifier
use three conductors. . .the output of a balanced power
amplifier use only two.

Many amplifiers use the input (-) signal and ground point and
output (-) as the same reference. . .balanced amplifiers create
a new (-) signal that is controlled by the amplifier circuit. It should
never be connected back to the (-) input signal. . . only connect
the (-) output to a speaker. . .it is more a matter of phase
correct in the balanced amps. . .check out Pass Labs articles.

Many if not all Class-D/Class-H/Class-S/Class-T amps use this
topology. . .Some Class-A and Class-AB use it also. . . in the
end it means that the (-) is not really based on the ground
reference. . .

The amp should provide a dedicated ground connection for a true
ground reference. . . both the (-) and the (+) output will have
electric potential. . . both can shock you!

You will not have to make changes to your loudspeaker inputs. . .
the balanced output amplifier will drive them with two conductors. . .

A lot of scattered points. . .pick the one you like.

I couldn't find that model on the internet. . .will do more of a search
after I post.
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Old 8th May 2008, 08:39 AM   #3
gupsta is offline gupsta  United Kingdom
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Thanks. The current version of the amp is here bk electronics . The only difference as far as i know of is that the older model i am getting uses xlr instead of speakon type connectors.
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Old 8th May 2008, 10:23 AM   #4
sreten is offline sreten  United Kingdom
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Default Re: balanced signal

Quote:
Originally posted by gupsta
I should be getting a bk electronics mfx600 soon, which has balanced outputs. xlr i think.

Quote:
Originally posted by gupsta
The only difference as far as i know of is that the older model i am getting uses xlr instead of speakon type connectors.

Hi,

I think you are confused. It may have balanced inputs. XLR cannot
be used instead of speakon and XLR is never a speaker output.

/sreten.
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Old 8th May 2008, 10:58 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
it is possible that an older unit uses the XLR socket as the speaker output.
But, only the two poles required for the speaker are used to connect the cable to the speaker.

I see they specify 220W into 8r0 and 310W (-1.52dBV) into 4r0. The output current into low impedance loads is crippled by some bottleneck in the design.
Three output pairs should get to near 390W (-0.5dBV) into 4r0.
I suggest that this amp is used to drive 8ohm speakers.
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Old 8th May 2008, 04:05 PM   #6
gni is offline gni  United States
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You will have to wait until the unit arrives and send
a photo of the back. . .if the unit comes with XLR on the
outputs. . .then I wouldn't hesitate to change them to
some sort of binding post. . .someday someone will
think it is a good idea to connect it to another piece
of equipment and kill the second unit. . .

I have seen XLR used for power supply to unit connects
and I don't like it. . .makers of electronics really need to
use XLR for balanced signals only and use other connectors
for speaker level signals and still another for power connections.

From the pictures it looks as if there is enough room to
modify the unit with suitable binding posts. Apparently
some countries (According to Pass Labs) are no longer
allowing amplifier binding posts to accept banana plugs. . .
probably a good call since banana plugs are used in test
equipment that are outputs and thus the ability to destroy
one or the other or both pieces of equipment. Spades are
good but I use spades on my Rane VP12! Mixing high level
signals and low with the same connectors is not good.
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Old 8th May 2008, 04:19 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
banana plugs are banned in the EC for the few manufacturers that care to take the safety of their users into account.
The reason being that the plugs can be inserted into some unshuttered mains sockets. Shuttered sockets can be overridden but are generally safer.
Similarly high output voltages on the banana sockets could come into contact with inquisitive & wet baby fingers.

Many manufacturers ignore this safety ruling and for some reason the Authorities allow importation of substandard equipment.
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Old 8th May 2008, 04:36 PM   #8
gni is offline gni  United States
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That is interesting that the mains in England/Europe are the
same type of connection. . .That is really scary. . . .Maybe a good
time to stop the use of banana plugs. . . .
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Old 8th May 2008, 05:03 PM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
UK & EC are different.
But they have tried to unify the rules. (and still trying).
UK uses 13A shuttered square pin sockets/plugs. The old unshuttered 15A, 5A & 2A round pins plugs/sockets although not obsolete are not generally used for power distribution.
But, on the Continent, a variety of shuttered and unshuttered round pin standards are in use/misuse daily.
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Old 8th May 2008, 05:36 PM   #10
rob3262 is offline rob3262  United States
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Default Re: Re: balanced signal

Quote:
Originally posted by sreten

Hi,

I think you are confused. It may have balanced inputs. XLR cannot
be used instead of speakon and XLR is never a speaker output.

/sreten.

Agreed - XLR is line level input/output, not amplified signal.
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