A/B Switch boxes for comparing amps

I’ve been experimenting with using this switch box to quickly change which amplifier my headphones are connected to for purposes of comparing them:

So far so good, but I’ve seen others post here about how unplugging headphones from the amplifier while audio was being played could damage equipment. I assumed it was because of the interaction of the TRS plugs, but now I’m not so sure. Is it safe to use a switch box like this while music is playing?

Or do I need to get this, which has a “Power” mode specifically for switching among amplifiers?

Also does anyone know a good way to switch between amps using balanced XLR ouput?

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You could use this for comparing three DACs with balanced XLR outputs feeding into an amp, or for any similar comparison.

They also make a version which sends an XLR signal to one of three outputs if you wanted to compare three amps from one DAC.

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I have the same lingering doubt. I was going to get the same unit you have for the same purpose, but went with this one in the end:

I haven’t received it yet, so can’t comment on its functionality - except to say the 3.5mm connections are an additional layer of faff.

I don’t know if @Torq is still around, but I imagine this is the sort of question he would be able to answer definitively. @frkasper also has a much better understanding of the technicalities than I do.

In lieu of that, I’ve seen at least one YouTube reviewer (I forget who) using the Sescom unit to switch between amplifiers with music playing with no (declared) ill effects.

I suppose a rapid pause-switch-unpause approach might mitigate any risk (assuming there is a risk to mitigate).

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Yeah I saw that but I’m trying to switch between two or more amps onto the same headphone using their balanced XLR out, which is 4-pin.

I’m thinking because the unit I currently have will switch two mono TS plugs that I could, in theory, get adapter cables to “translate” 4-pin balanced XLR to/from twin mono TS plugs (L and R). However I can’t find the appropriate cables so would have to either have them made or make them myself.

I think GoldenSound uses a switch box like mine. At least it looks like mine. Also I’m realizing that the “Power” mode in the second Douk unit I linked to likely merely bypasses the volume control and all the rest of the electronics in that unit are just relays so that you can switch using the remote. I may just pick up that unit anyway as I believe it could easily be adapted for blind testing using a computer to mimic the remote control. :smiling_imp:

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You can build one fairly cheap-ish. Need an enclosure, a selector switch, hookup/microphone wire, and male + 2 or 3 female chassis mount XLR connectors.

Box:
https://www.goldpt.com/enclosures.html

A 4P3T1D Goldpoint selector switch

Xlr plugs:
https://www.redco.com/PC-Mount-XLR/

There may be a need to put 600 ohm resistors across the + and - L and R input connectors so that the amp still sees a load when switched, instead of having the connection suddenly get cut when you switch. That’s just a hunch on my part, maybe ask a diy community or EE about that.

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I think you need one of these:

If you look on eBay, they’re going used pretty cheaply. Nice wooden case, too.

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Does the lovely operator come with said bundle. :wink::grinning_face_with_smiling_eyes::rofl:

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Assuming we don’t fry our amps in the meantime, some sort of random blind-switching mechanism is definitely the logical next step.

I’d be really interested to hear how you get on if you do pursue this - I’d love to be able to conduct my own blind testing (albeit with known amps) without having to enlist the help of a third party.

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Good point. Or modify an existing switch box. But I think making my own adapter cables may be a better investment since I can re-use the same switch box.

Now I’m leaning towards getting this

getting three of these

and modifying one to female XLR. I’d have to test the switch box to make sure it isn’t using a common ground though.

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I thought @pennstac was talking about the operator. I already have the proper cables and plugs. :smile:

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Found this article about switching between two amps and one set of speakers:

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From the linked article:
" Is it possible to use a speakers selector switch in reverse for this? Well, not really. There are three problems with the majority of speaker switching boxes. One is that they usually have common ground . You do not want to have common ground between two amps, this could negatively affect their performance (and sound quality) and in some cases also case damage – there are amps that have fully balanced outputs and cannot have common ground between speaker connectors, for example some Class D amps."

I just checked the switch box I am using for switching TRS single ended headphone output and it does share the ground. :disappointed:

Because the switch is actually switching pairs of TRS connections I should be able to rewire it, though.

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I’ll keep replying to myself as there seems to be a bit of interest.

I did the rewire a few days ago and I’ve been A/B testing amps since then. So far so good. It was easier than I thought, no soldering. I just rearranged the pins in the interface plugs.

If you’re confused as to why that would work, realize that there are 5 wires going to each of the four pairs of TRS plugs. LR for each of the plugs and a common ground. The ground is also common on the switch side but the other four wires are switched. In fact the board for the switch is labeled XLR Balanced Switch so I’m sure it’s the same one Douk uses here: https://www.amazon.com/Nobsound-Audio-Balanced-Converter-Selector/dp/B07QVKPR2V. I simply disconnected the ground wire and the LR wires leading to one of the plugs and then connected the ground wire to where the L wire used to be. Because I did this on both the inputs and the output plugs, the common ground in the switch is no longer part of the circuit.

If anyone wants to make the same mod and needs more detailed instructions, just let me know.

Next I’m looking into a unit with an IR remote and speaker terminals. I plan to make adapter cables so it can be used to switch both single ended and balanced headphone connections. Then I’ll probably whip up some IR transmitter on a computer to randomize which input is used so I can blind A/B test. There are a couple of units I’m considering. I’ll post here if/when I choose one.

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