Are the days of cheap 400/700s done.

[Oldskoolfan]

You can bridge the Phase Linear amplifiers, but you have to do it correctly. The 700B Owner's Manual says to never connect the outputs together!

There was an undated Service Bulletin describing the technique for correctly "Bridging" the 400, 400 II, 700, 700B, and 700 II into 8 Ohms or greater (attached). It mentions the use of a phase shifting Line Input Transformer. With the Left and Right Input Signals 180 degrees out of phase, the output is taken from the Left and Right Positive Speaker Binding Posts. The Output is summed by the two channels to double the wattage. The Line Input Transformer mentioned, TRIAD G-336, is no longer available.

A substitute Line Input Transformer is available here:
https://lightningboyaudio.com/store/p70/UJ20_line_input_transformer.html#/accounts
I have spoken to the technician at Lightning Boy Audio and they do have this in stock at $78.00. I would be curious to hear about your bridging adventures.

That may be a good plan B.
Could you look at Plan A in post #40 and tell me what you think?

 

[TimD]

Build *just* U5B from the schematic - that's the actual line level inverter. The rest is a crossover, none of what you need to bridge an amp (and you only need a *single* amp to bridge). If you are trying to do a sub setup, that looks like it would work as a crossover. If you have two subs, and want to run bridged, then you may want/need two amps, since the lowest tolerable load impedance is twice that of single channel (think of it as half the load on each channel . . . not exactly whatnis happening, but gets you there . . .

 

[Oldskoolfan]

Build *just* U5B from the schematic - that's the actual line level inverter. The rest is a crossover, none of what you need to bridge an amp (and you only need a *single* amp to bridge). If you are trying to do a sub setup, that looks like it would work as a crossover. If you have two subs, and want to run bridged, then you may want/need two amps, since the lowest tolerable load impedance is twice that of single channel (think of it as half the load on each channel . . . not exactly whatnis happening, but gets you there . . .

I need the functionality of the active crossover since this is designed to tap off a preamp output. So do you think this will work to bridge an unmodified PL400?

 

[TimD]

Absooutely anything that can provide an inverted signal to one channel and a non-inverted signal to the other can bridge an amp with a common ground for the two outputs (the only things that won't bridge are amps with differential outputs, and a few other oddities). There is absolutely nothing magic or special about a PL in this regard.

 

[mlucitt]

Could you look at Plan A in post #40 and tell me what you think?

I don't know the cost of a Rolls SX95, it seems very complicated if you just want to bridge two channels of a stereo amp for a single output to feed a subwoofer. Phase Linear recommends a small metal enclosure to prevent any environmental noise and it could be handy to install Input and Output RCA Jacks. No power required. It would be my Plan B.