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I’m a strong believer in full balanced topology. Compared to single-ended circuits having RCA connectors, a true balanced signal source will typically output the music and a completely phase-shifted representation thereof. As a result, the receiver can reject anything that both signals have in common. This behavior is also known as common-mode noise rejection. In theory, this method ensures a very low noise floor during audio signal transmission. Longer cables are also not a problem. Full balanced topology comes at a price, though because of duplicate circuitry. Keep in mind though, that by simply slapping an XLR connector to the back of your Hifi gear doesn’t necessarily mean its circuits are internally true balanced.
The Problem with Balanced Signal Topology
For instance, My Gustard X20 is internally fully balanced and so is my Hypex nCore power amplifier. When I added my newly built XONO phono preamp clone (which is also balanced by design) to the mix, I felt I was spending more time unplugging cables than actually listening to music. My problem was that I needed a super-flexible preamp with multiple XLR inputs. Unfortunately, even the most expensive ones from Burmester or Accuphase come with 1-2 inputs at best. And there was no way I wanted to spend that kind of crazy money.
In my setup I need to be able to switch between the Gustard, the turntable and potentially a third XLR source. It would also be nice to have a pair of RCA inputs just in case. But it gets even more difficult since I also need to be able to toggle between two outputs. Those would be either my KGSSHV headphone amp or my Hypex nCore power amp.
I initially planned to build a passive “switchbox” for my needs but gave up as soon as I had worked out the total cost (sigh). Decent quality XLR terminals and wires don’t come cheap and wiring is a nightmare.
I was thrilled to find EXACTLY what I was looking for on Amazon (at a ridiculously low price) made by a Chinese manufacturer. It’s called a 2-in 1-out XLR switch. My Nobsound Little Bear MC3-IN-3-OUT (advertisement link) is actually a 2-out XLR switch. Since it only performs signal switching duties, it’s entirely passive with no power supplies. Build quality is quite sturdy and the looks are reminiscent of earlier Naim gear from the 80s. At least my wife doesn’t complain about its looks :)
The Little Bear features two rotary selectors to switch between XLR sources and outputs. I have both of my “input sources” hooked up to 1 and 2. My DAC is input #1 whereas the turntable is hooked up to #2. The second selector allows you to choose the desired output. With the output selector I can conveniently toggle between headphone and power amp. Easy and brilliant! I’ve had zero pops or clicks when toggling inputs or outputs.
But it gets even better since the little unit can also convert between XLR and RCA which is fantastic if you haven’t got an adapter handy and need to feed an unbalanced signal into a balanced amplifier or vice versa. I wish there was a remote control version and I’d gladly pay for that convenience but I’m ok with a manual solution.
I haven’t had time yet to open up the box to inspect wiring. As far as I can tell from Amazon’s product images all XLR terminals are soldered to a PCB and connected using ribbon wires. You could in theory mod the unit and add audiophile-approved cables. However I cannot hear any difference when the box is in the signal path which speaks for its quality. So why bother tinkering with a perfectly working product.
Here’s how I have my Little Bear MC3 set up if I want to listen through speakers (KGSSHV headphone amp is connected via XLR to output B):
Common Usage Scenarios
If you need to add additional inputs or outputs to your existing audio system, don’t just buy another preamplifier. A good switch-box could do the trick. You can even chain these units almost infinitely by connecting the output of a Little Bear to the input of another Little Bear box.
Converting Unbalanced to Balanced (and vice versa)
In a heterogeneous audio environment, it’s often quite handy to mix RCA with XLR even if just for sonic comparisons.
Performing Listening Tests
If you want honest A/B comparisons between audio gear, units like the Little Bear MC3 will allow you to do that.
Improving Sound Quality
Many preamplifiers have inferior relay-based input selectors that can potentially degrade overall sound quality. By using a switch-box solution, you can entirely bypass those limitations.
Building a Passive Preamplifier
In many setups, a simple passive volume control is just as good as a multi-thousand dollar preamp. It has zero distortions because of the lack of active circuitry. You may however want an input selector, too which is where units like the Little Bear MC3 may become your best friend.
Definitely check out switch-boxes like the Little Bear MC3 which can save you a lot of money. According to my listening experience, there’s no sonic penalty. For under $70 you will probably have a hard time finding anything better.