Mulder
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If I want to blind test two different amplifiers with the same pair of speakers and the same preamp/DAC, what do you recommend I use to switch between the amplifiers.
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Blind testing amplifiers.
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DVDdoug
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You can find switch boxes. Usually the same switch can be used whether switching speakers or amps. Or if they both have banana plugs (or some kind of connector) whomever is doing the switching can switch manually. With an ABX test it's pretty common to switch the connections manually, and to unplug every time even if they are re-connecting the same thing.
Assuming you are doing an ABX test (or similar) you'll need to make sure there is no "click" or other give-away when A or B is connected. And if you get a switch, it's best to get a 3-way switch, or a switch with an off-position, so it can be turned-off when you "switch" from A to A.
Assuming you are doing an ABX test (or similar) you'll need to make sure there is no "click" or other give-away when A or B is connected. And if you get a switch, it's best to get a 3-way switch, or a switch with an off-position, so it can be turned-off when you "switch" from A to A.
I personally prefer to do AA, AB, BA, BB testing, where the switching is random, and the test is to be able to distinguish A from B with statistical validity. I find that ABX testing where X has to be identified as either A or B doesn't work for me, as by the time I've heard X, I've forgotten what A and B sound like, so end up guessing. The AB, BA, AA BB test, with rapid switching back and forth is exquisitely sensitive to small differences. It also just requires the answer 'same' or 'different'.
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Sokel
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Depending on the amps you might not want to get one who leaves the amp's output open.
Some don't like it.
On the other hand it goes without saying what you need a good quality one or else you might end up with a truckload of recycling materials.
Some don't like it.
On the other hand it goes without saying what you need a good quality one or else you might end up with a truckload of recycling materials.
kemmler3D
Master Contributor
Whichever switch box you get, don't forget you need to match levels very precisely for the test to be valid. The commonly cited number is 0.1dB or so, at the speaker terminals... you will need to use a multimeter for this.
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Might be helpful to know which two amps and which speakers you'll be using.
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You'll want to place a 220 ohm 2 watt resistor across the outputs of the tube amp. That way when you switch away from the speakers it won't go into oscillation from having no load. Otherwise you could cause damage to the tube amp. That was one of the reasons I thought it good to ask.
ABX tests done correctly allow you to switch between A, B and X as often and early as you like. Which makes them tricky for amp testing.
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Maybe some other folks have better ideas. I think using 2AFC might be more practical for this test. It is often used in food testing. You choose a preference. The one you like better. 2 alternative forced choice. The forced choice means you have to pick a preference even if you think they sound the same. Believe it or not you can sometimes pick reliably one as different even if you think they are sounding the same.
The reason it is more practical than an ABX test is you know each time you switch you are listening to different amps. You just don't know which one is A and which is B. So with an amp switcher doesn't matter you always will be swapping from one to the other and not from one to the same one. You still need to randomize which is A or B first for each trial. But for each trial you can switch back and forth knowing for certain it is a different amp until you think you have a preference. The statistics are simpler to. If you achieve a consistent preference 75% or more of the time you heard a difference at only 5% or less chance of this being a random result. I'd say you need to do at least 20 trials.
Two other things, be sure you check for polarity inversion between both amps. Also check channel to channel balance by checking signal level on both channels of both amps.
The reason it is more practical than an ABX test is you know each time you switch you are listening to different amps. You just don't know which one is A and which is B. So with an amp switcher doesn't matter you always will be swapping from one to the other and not from one to the same one. You still need to randomize which is A or B first for each trial. But for each trial you can switch back and forth knowing for certain it is a different amp until you think you have a preference. The statistics are simpler to. If you achieve a consistent preference 75% or more of the time you heard a difference at only 5% or less chance of this being a random result. I'd say you need to do at least 20 trials.
Two other things, be sure you check for polarity inversion between both amps. Also check channel to channel balance by checking signal level on both channels of both amps.
Roland68
Major Contributor
The most important thing is that the ground is separate and is switched in the same way as the + line.
Most finished devices are equipped with very simple switches and very thin cables, which is why I built my box myself.
A high-quality switch costs around €10 - €25. With the right connections, everything can be crimped and screwed, no soldering required.
You can also set it up as a switch with a completely insulated cable breakout, without any housing.
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