In the studio, being able to split a signal is simply a fact of life. It's often also a source of multiple problems: ground loop hums and buzzes, signal loss, phase alignment problems, bad tone, etc. The Lehle P-Split 2 is a nifty and inexpensive solution, and it's made for high-impedance connections, such as a guitar, pedals, and guitar amp.
Let's say you need to take the output of your guitar or pedalboard into an amp but also a direct box so you can possibly reamp later, or combine the signal with a modeled amp. And if you reamp, you need something that can take a balanced signal and output an unbalanced one.
Or maybe you want to run two amps. Or an amp and a modeling box.
In either case, what you don't want is hums, buzzes, ground loops, loss of tone, or phase reversal.
Basically with this box, you can do all that stuff and avoid all of the above problems.
Lehle is a German company whose owner absolutely "gets it" and all of its products are built with the very best parts. Even the enclosures are beyond solid, and come with thoughtful touches like top-mounted screws, so that you can use the two provided additional screws to attach the base plate to your pedal board, reattach the top, and have an attachment that is better than velcro (this isn't necessary to do, however, rubber feet are also mounted on the product or you could always attach velcro). I didn't attach mine to anything because I see it as a solver of studio problems of many kinds, as I will explain further.
I could go on and on about what this thing does, but here's the important thing: it's the best of its kind I've found in 25 years of recording work.
Most AB or ABY boxes have no way to lift the ground. So if you want to use two amps on stage or in the studio, whether combined or one at a time, you will get lots of hum and noise. Whether on stage or in the studio, ground loop noise is absolutely unacceptable.
Most AB or ABY boxes also can't solve the problem of two out of phase signals causing phase cancellation that can make the sound thin (this doesn't always happen, but when it does, it makes you want to pull your hair out). This is also not something you want to have with your audio.
Most AB or ABY boxes alter your tone in bad ways. This is because they either provide too much resistance, or if they have transformers to isolate both signals, most have transformers that sound really bad. And I've had boxes incorporating some of the known "standard" transformers that just killed my tone. After all, transformers often have a "sound," and that isn't a good thing if you've worked carefully to create your personal sound.
The P-Split 2 does no bad things to your tone. In fact, it's absolutely transparent; at least, I was not able to hear a difference in my tone with the box in the signal chain. No difference in tone is good.
To test the isolation transformer's ability to kill ground loop noise, before installing the box in my chain, I used a standard AB box to send the signal to both amps. As expected, there was quite a bit of hum and buzz simply by virtue having both amps connected to the AB box.
I then replaced the AB box with the P-Split 2. With the ground lift switch in, both amps were dead silent, the ground loop noise was killed completely. Switching the ground lift off made the hums and noise return. This thing works.
It has both balanced and unbalanced capability. You can find a manual explaining how to use this feature that can be downloaded as a PDF by googling the product. A balanced signal lets it be used as a direct box with a recording interface or sent to, say, an effects box with balanced line inputs. It also lets it be reversed and used as a re-amping box.
The important thing is that the tone of the signal is unaffected. You can even use it in a single amp rig, between amp and pedal board, if attaching your pedal board is making your amp hum (this assumes, of course, that your pedalboard isn't having its own hum issues just from the pedals being connected to each other or a power supply or two).
This box has no footswitches. They make one that does, but you may not need switches so you might as well save money. This thing runs only $169. That's a good price for a gadget this good.
So if you're running two amps and only want to hear one, either put the second amp on standby or turn its volume all the way down. Lehle makes one with switches that does all the same stuff, but in the studio that's not something I need. Switches are expensive, and the Lehle that has them costs $229 and has to be connected to a power supply. The Fulltone box, which is the only other one I'd recommend, is $239.
The P-Split 2 needs no power supply at all, nor does it need batteries. It's 100% passive.
This is a great tool -- if you have a studio, it's a must-have. And because it costs $70-80 less than the only other decent switchers out there (namely, Lehle's own product with switches, and the Fulltone ABY) it's a bargain.
A lot of players like the competing products by Radial. While I think Radial makes good stuff, I have found that their similar product gives my guitar a "crinkly" tone. I can't describe it any other way. That may just be my guitar and amp combinations, but that's my finding. So for studio use...not for me. Fine for live.
In the past, I haven't liked to record more than one amp at a time, because usually it's more trouble than it's worth, but today I got some beautiful tones combining my two amps while testing this box out in my rig, and I can say for sure that it will get a ton of use. This is what it looks like. As you can see, there's nothing to break or wear out, it should last forever: