Hi there all,
I have a mate whose in a band, they only have one guitarist and no bassist, and hes absolutely useless at everything gear related, so i help him out sometimes like a techie. usually when theres just one amp going it seems really empty, so i came up with slaving two heads and two cabs together.
What i came up with is to plug the guitar into amp A, then run a lead from the effects send of A into the input of amp B (from my understanding this is just the preamp from A going into B, much like an effects processor) and this lets both amps run cabs still and create two different sounds (from different parameters)

My question is, is this safe for the amp, and indeed the people in the vicinity?
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I think that you could accomplish a similar effect by running just one head/combo and a cab.

But if you want independent control, you could also buy a y-splitter and split the signal from the guitar into both. I know that'll be okay.

As for the people listening, well, it depends on the wattage, etc. of these two units.
As long as you have some type of load on each amp head, you should be fine. I use the line-out on one of my amps to run it into a separate power amp, & the power amp just amplifies the wide-open first amp, with overall volume regulated by the power amp master volume. The first amp has a load box connected in place of a cab (I use either a THD Hot Plate or my Palmer PDI 03 as a load, depending on the setup).
This setup gets you beautiful tube overdrive & superior dynamics at any volume.
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well one cab will have massive bass to fill, the other will have more treble and mids to cut through, it gives the effect of two guitars if theyre on opposite sides of the stage, plus hes a cheapo and cant afford a decent Y splitter, such as the framptone, we use the house amps (usually marshall JCM2000's) and usually played LOUD x thanks anyway
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why dont you just run the cabs in stereo, whats the ohm output on the head and ohm inputs on the cab?

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Considered using something like Jack White does? Like a POG? And using the two outputs to go to different amps, one to get the sub-octave and cover the bass? Just a fun thought.