Bridging Lanzar Amps

from a post by
Peter Foote on the BASSlist
Does anyone know how to wire up the [Lanzar] amp for bridged mode?

The bridging is done by switching the little switch on the board and then using any 1 of the inputs. The driver is connected between the OUT terminals.

In the amp circuit one of the channels is inverted as compared to the other (look at U1A and U3A on the schematic). I think that OUT1 is the inverted channel unless there is another inversion performed on both channels later in the circuit.

Therefore, one of the speaker outputs is inverted when compared to the other. If you feed the same input into both channels and then connect a pair of speakers up with the OUT's as the positives and the COM's as the negatives, one of the speakers will be out of phase.

When the amp is manufactured, one of the OUT's will be brought to a -ve terminal and one of the GND's will be brought to a +ve terminal (in other words, one of the outputs would appear to be connected backwards). Then, if you hook up two speakers normally, they will be in phase. If you want to bridge the amp, the driver would go between a +ve and -ve terminal. This whole inversion of one channel in the main circuit is done for two reasons.

One, to get rid of an extra op-amp stage that would be required for the bridging. Two, to provide a connection scheme that always gives the user a +ve and -ve terminal to connect their driver(s) to.

As a note, all bridgable amps have a common ground with two output output circuits and then the driver is connected between the outputs (even if it one is marked as -ve) for bridging. If the amp has a signal on both channels then it is already bridged internally. The only exception would be an amp with a floating supply for each channel.

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