Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on December 17, 2010, 03:28:39 pm
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What should be taken into account when connecting two identical power amps to a bridge circuit?
Is that at all possible if the channels have a common ground?
How should I wire a 4-pole Speakon jack having markings 1+, 1-, 2+, 2-
a) if I just replace a traditional 1/4" jack with it
b) if I want to give a possibility to use the output for bridge circuit?
/Leevi
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(http://upload.wikimedia.org/wikipedia/en/thumb/8/8e/Bridge_amp.GIF/200px-Bridge_amp.GIF)
Example. Two amplifiers, each rated 100 watts maximum into 4 ohms, in bridge mode they will appear as a mono amp rated 200 watts into 8 ohms. This is the most commonly misunderstood mode of operation and it requires additional circuitry to implement if the pair of amplifiers does not have the facility built in. The image shows two identical amplifiers A1 and A2 connected in bridge mode. The signals presented to each amplifier of the pair are caused to be in anti-phase. In other words, as the signal in one amplifier is swinging positively, the signal in the other is swinging negatively. If, for example the maximum output voltage swing of each amplifier is between a peak of + and – 10 volts, when the output of one amplifier is at + 10volts the output of the other will be at –10 volts, which means that the load (a loudspeaker) now sees a 20 volt peak difference between the “hot” (normally red ) output terminals.
(http://upload.wikimedia.org/wikipedia/en/thumb/4/4d/Parallel_amp.GIF/220px-Parallel_amp.GIF)
The image shows two identical amplifiers A1 and A2 connected in parallel configuration. This configuration is often used when a single amplifier is incapable of being operated into a low impedance load or dissipation per amplifier is to be reduced without increasing the load impedance or reducing power delivered to the load. For example, if two identical amplifiers (each rated for operation into 4 Ω) are paralleled into a 4 Ω load, each amplifier sees an equivalent of 8 Ω since the output current is now shared by both amplifiers — each amplifier supplies half the load current, and the dissipation per amplifier is halved. This configuration (ideally or theoretically) requires each amplifier to be exactly identical to the other(s), or they will appear as loads to each other.
http://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers
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Thanks Butterylicious,
So in the first example the output signals should be in opposite phases?
Does this mean then that it must be possible to invert the phase in one of these identical amps?
There could be a switch where the polarization could be changed.
(http://)
Is the following wiring proposal according to the standard wiring?
(http://)
/Leevi
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Yes. For a true bridge, 1 amp must be inverting and the other non-inverting. In sand state amps, typically they use a switch to swap an opamp input on one side. You'll also notice the bananna post jacks go - + + - so you can simply move the speaker plug. You could build a little PI ahead of both of the identical amps to create a differential input splitter.