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I'm hoping to get some clarification on how to probe a full bridge multi-channel amplifier (ch = 2/4/6/...) that has only 3 outputs for 2 channels. I.e. for a 2 channel it would be:
Ch1 Ch 2
+ -/+ -
Hmm, that looks unusual. How, exactly, do you connect a speaker to the above (specifically, is that +/- terminal used)? Are speakers coming with center-tapped voice coils now?
1) how would one probe this amplifier? I've attempted probing it normally, and with the scope on Ch 1's + and Ch 2's -, basically bridged mode, without success. Am I correct in assuming that in this case I would need to use the amplifiers actual input ground (12vDC ground) for the scopes ground instead of the negative rail? Obviously I would then only get half of the waveform, which is fine for detecting clipping, and I'd need a 2ch scope to get the whole waveform?
For a typical bridged output - which is floating with respect to "ground" - you need to use a floating or differential measurement technique. That could be with an isolated scope (which few people own), a differential probe (much better) or, if your scope has at least two channels and supports basic math functions, you connect the probe tips from two channels to each side of the bridge, respectively, then subtract one channel from the other (the probe grounds can be connected to power ground, if available, or left floating).
There are numerous other tricks that can be done so don't consider the above an exhaustive list.
2) Does this mean the center shared -/+ has the full sine wave on it, with each half 180 degrees out of phase? Could I just probe this while referencing the input ground?
That's the proverbial $64000 question. In a typical bridged amplifier you have two half bridges which are fed signals that are inverted with respect to each other so when the load is connected between them it sees double the voltage, which quadruples the maximum power (assuming there is sufficient current available). This almost seems like a push-pull output stage, but that is really only used in tube amps and power supplies, so very puzzling. Got a make/model number for the amp so we can see how it is supposed to be used?