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Old 26th December 2011, 06:19 PM   #1
reins is offline reins  Germany
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Default Briged amp from Balanced Input Signal

Hi,

Following setup:
- I have a balanced signal from the source (DI-Box)
- I would like to go into a hifi amp, with '+'-signal on right and '-'-signal on left.
- now I would expect the reverse audio signal on the both amp-outputs.
- feed a 8Ohm speaker with right channel 'hot' and left channel 'hot'

Would this work?
Should I connect the ground-output posts?

Thanx
Stephan
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Old 26th December 2011, 06:49 PM   #2
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It should work,providing that the amps have identical gain.
And if the driving signals have an Identical voltage level.
No you do not need the ground posts.

Jer
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Old 27th December 2011, 01:18 AM   #3
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One issue that you encounter with the idea you propose is the due to the behavior of the amp channels with respect to the speaker and each other, the impedance of the speaker will appear to be half what it is specified as on the speaker. In other words, the amp would think that an 8 ohm speaker is a 4 ohm speaker, etc. This is ok if the speaker impedance is high enough, and the amp is built well. However, if the amp doesn't have a lot of extra current capability on the output, and/or the speaker impedance is below 8 ohms, then you may destroy the output of the amp, and maybe more.

Peace,

Dave
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Old 27th December 2011, 09:43 AM   #4
reins is offline reins  Germany
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Quote:
Originally Posted by dave_gerecke View Post
One issue that you encounter with the idea you propose is the due to the behavior of the amp channels with respect to the speaker and each other, the impedance of the speaker will appear to be half what it is specified as on the speaker. In other words, the amp would think that an 8 ohm speaker is a 4 ohm speaker, etc. This is ok if the speaker impedance is high enough, and the amp is built well. However, if the amp doesn't have a lot of extra current capability on the output, and/or the speaker impedance is below 8 ohms, then you may destroy the output of the amp, and maybe more.

Peace,

Dave
That is one reason for bridging, that I would be able to get more power into the 8Ohm speaker
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Old 27th December 2011, 09:44 AM   #5
reins is offline reins  Germany
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Quote:
Originally Posted by geraldfryjr View Post
It should work,providing that the amps have identical gain.
And if the driving signals have an Identical voltage level.
No you do not need the ground posts.

Jer
By the way, what will happen, if the voltage level of the two channels differs by a higher margin?
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Old 27th December 2011, 05:27 PM   #6
reins is offline reins  Germany
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Talking Bridged amp from Balanced Input Signal

I checked it today, it works!

Thanx
Stephan
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Old 28th December 2011, 02:59 AM   #7
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It should also work if you connect the + output from the source to BOTH the + inputs of RIGHT and LEFT, then connect the - output from the source to the signal ground on BOTH the RIGHT and LEFT inputs.

In this configuration, your speaker would be connected to + on the right and - on the left.

Same result either way.
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Old 28th December 2011, 04:53 AM   #8
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Quote:
Originally Posted by barnabas1969 View Post
It should also work if you connect the + output from the source to BOTH the + inputs of RIGHT and LEFT, then connect the - output from the source to the signal ground on BOTH the RIGHT and LEFT inputs.

In this configuration, your speaker would be connected to + on the right and - on the left.

Same result either way.
No that will not work !

The Inputs to the amps must be out of phase what you just described, The phase of the input signals will be the same and then you will get 0V difference between the two outputs regardless of what the input signal level is.

Also if the signals are not of equal value then you will have one channel fighting the other and the uneven cancellations will result in higher distortions.

Anyway I am glad to hear that you got it working !!!

Cheers !!

jer
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Old 28th December 2011, 12:59 PM   #9
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Quote:
Originally Posted by geraldfryjr View Post
No that will not work !

The Inputs to the amps must be out of phase what you just described, The phase of the input signals will be the same and then you will get 0V difference between the two outputs regardless of what the input signal level is.
The phase of the OUTPUT signals will be 180 degrees out of phase... that is why I said to connect your speaker + to the LEFT and speaker - to the RIGHT. The + outputs of the amp will be IN PHASE, but the opposite outputs will be OUT OF PHASE.

If it won't work, then my amplifier must exist in a parallel universe where everything works opposite of how it works in our universe.
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Old 28th December 2011, 01:45 PM   #10
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"The + outputs of the amp will be IN PHASE".
No this will not work !
That will work as a paralleled amp operation, But, not a Bridge Tied load configuration ( hence BTL or Bridged).
The outputs of the amp must be out of phase with each other.

In order to make this work.
1# the source ground goes to the amp inputs ground.
2# the source + connected to the right amp input.
3# the source - connected to the left amp input.
4# the speaker + connected to the right amp + output.
5# the speaker - connected to the left amp + output.

This way the amp signals will be out of phase as they need to be in order for it to work, and, the speaker will be in phase with the source signal.
Both amps - output (or ground) are not connected to any thing at all.


jer

Last edited by geraldfryjr; 28th December 2011 at 01:50 PM.
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