Best way to A / B test amps? Use a switch?

I built my own switcher using multiple speaker relay paralleled to minimize contact wear causing distortion.

Or use a abx-switch-comparator

Problematic if you are talking about tube gear that doesn't like to be on when no speakers are connected, but no problem with solid state.

Just have a friend hook up one at a time - a swap of interconnects from one to the other (when muted, of course) takes a minute - turn them off if worried about it.

Listening blind and not knowing which is on is the acid test of whether you are really hearing a difference or imagining one based on cost, expectation etc.

Problematic if you are talking about tube gear that doesn't like to be on when no speakers are connected, but no problem with solid state.

Connected to a dummy load resistor before disconnecting speaker from a tube amp can solve the problem, and no need to power off the tube amp to eliminate warm-up time.

I believe that the mind forgets what it heard 5 mins ago and internal biases kick in strong.

Yeah, my head was once stuffed full of this exact same nonsense. True story, I drove 200 miles to a store to compare interconnects just because they had this device that allowed you to switch back and forth instantly. Yeah. So I drove 200 miles to hear for myself.

Only when I got there, owner says sorry, we had to send it back. But you're welcome to compare anyway. And showed me the amp and let me alone.

So I listen to his interconnect a few minutes. Okay. Whatever. Flip the source. Swap interconnects. Flip the source. And.... WTF!!!! I mean WTF!!! Thought for sure I had messed up this guys beautiful expensive tube amp. Could not cut it off fast enough. What the.....?!?!? Everything hooked up right. Well then.... what?

Gradually it dawns on me. The freebie patch cord I had brought along to compare sounded so awful it was obvious instantly and from behind the speakers. Turned it back on, sat down, forced myself to endure what I had been playing and enjoying every night for years. Could. Not. Believe. It.

But hey, if you believe you forget, I believe you. Can only imagine how many fights you must get into with your wife, never being able to recognize her voice on the phone, but hey, I believe you. Really. I mean, that is after all why they have Caller ID, right?

Hahaha.. Pretty funny and I'm not saying you "forget" a blatantly obvious sound difference. We're not playing in that field here. Audiophiles are obsessed with the slightest nuances and to believe that your superior hearing memory is immune to certain biases is naive.

Everyone knows it's BY FAR better to A/B test with instantaneous switching than relying on memory and what you think you heard.  

Thanks for the other replies.  Unfortunately, I'm not up for building my own.  I would have thought there was something practical on the market already.

Constant switching will drive you crazy.  It is far better, IMHO, to listen to each piece of gear for couple of days to get feel what you like more.

Both approaches inform and have value.

@david_ten Yes, but comparing particular element, like bass or treble extension can result in choosing wrong gear.  In early seventies, before Transient Intermodulation Distortion surfaced, you could get a lot of amps with wonderful bass, treble etc, but sound of these amps was tiring over longer period of time.  When comparing such amp by switching, it would always win, but it was unpleasant to listen to on long run.

Running 2 systems myself. I build a switching unit with a break before make switch. It’s never a good idea to take a chance of accidentally connect 2 amps simultaneously. Something is going to give. Not hard to make and very cost effective. The switching is close to instantaneous. There are some switching units on the market you could try. Do not use speaker selector switches as the chance of having both amps connecting simultaneously is high in which case pop goes the weasel.  Break before make is the key phrase. 

@kijanki I’m in wholehearted agreement with you. I am also in wholehearted agreement with the "other" position and points made above.

I realize this (being in both 'camps' simultaneously) tends not to happen often in these environs.

I use both approaches. Each ’way’ can and does (though not always; and not always with certainty) offer unique and disparate information. This addresses non-overlapping areas of personal (human) interface and connection. Objectives for each ’approach’ focus on different natures / aspects.

Key (for me) is the overlay and the interlacing of the information gathered and how I use it to make a final decision and choice.

Everyone knows it’s BY FAR better to A/B test with instantaneous switching than relying on memory and what you think you heard.

Well, no, that is not the case at all.

First of all what you suggest is impossible. Even instantaneous switching still the goal is comparing. With what? With what you heard. When? In the past. Where’s the past? In memory. Nowhere else.

You simply haven’t thought this one through. Not at all.

Which aspects of the sound? Well how do you even begin to answer that one? By thinking over the different aspects. Which involves what, again? Memory.

All you’re doing with this instantaneous switching malarkey is moving the proverbial runner halfway to the finish line. You know the story, right? To get to the finish line he must go halfway, then halfway, then half of that.... never gets there. When in reality, WHOOSH! Right on by.

That’s exactly what you’re doing. Inventing some nonexistent constraint, insisting its real. When in reality, WHOOSH! Right on by.

Besides, what about warm-up? Break-in? Acoustic treatments? What about differences between recordings? Do you now require duplicate identical turntables just to decide which LP is better?

Its really just beyond silly.

Especially since, if the difference isn’t big enough you can still be sure after the 5 minutes it takes to change something out, then why would you care anyway? Answer me that one.

I would have thought there was something practical on the market already.

Well, there would be. If it would serve any purpose. Which it doesn't. So its not.

But seriously, the question stands: If you can't be sure after a few minutes then why do you care?

What about differences between recordings? Do you now require duplicate identical turntables just to decide which LP is better?

Absolutely.  Switching is just a distraction and works against obtaining whole picture.  In order to get whole picture you need to listen to many recordings over period of time.  Perhaps because of that many companies, like Benchmark, give free 30 instead of few days evaluation.

bring them to my house

Very good points.  Some of which I have considered but not enough.  

I still think the audiophile thinks his aural memory is much keener than it is and not susceptible to audio forum interference/influence.  But, you're right saying that the "over time" part is also very important.  And there are downfalls to switching as well.

The other part of the issue with me personally is I don't have time to deep listen for hours on end and my environment changes quite rapidly.

I have done extensive A/B comparisons between equipment.  Be it pre-amps, amps, DACS, etc.

My experience is to play a favorite song (say CD) at the volume you like.  remove the CD and play a white noise CD and measure the DB level with a meter.  Then swap the piece of equipment with the one you want to test.  Again play the white noise CD and adjust the level to where it matches the level of the previous unit. Record both unit's levels so you know where to set them when listening.

Making sure the levels are matched before comparing is absolutely important.

Now that you have established the two levels, go for it.

Listen to the first unit with music you know.  Then swap the new unit in. making sure to turn the amps off if swapping amps or mute pre-amps if swapping other stuff.

This has worked very well for me in making purchasing decisions.

enjoy

I still think the audiophile thinks his aural memory is much keener than it is and not susceptible to audio forum interference/influence.

Oh no. How? How could that possibly be the case? Only if maybe someone popped out of the womb and straight away started churning out Fremer-level reviews. Which no one ever did.

We all had to learn how to hear. We all struggled to attain whatever level we are at. For sure that was the case with me. Go read through my posts, you'll fine a whole bunch saying this same thing. Several long ones recount how it took me one full year just to learn to distinguish good DAC from bad CD. Then about another year developing that same skill to a level where- cones, footers, cables, elevators, fuses, panels, on and on-  it seems there's no end to the things that matter. 

And I don't need to match levels, or play the same track twice, or switch fast, or any of that. Which is by the way not bragging nor BS nor even all that unusual. The dealer I learned from never once played the same track twice, and Michael Fremer is somewhere on video saying, "I know some like to do that but I don't." 

That's not to say it can't help. When learning any sport- racquetball, golf, autocross- what's the first thing the coach always has you do? Practice. Break it down to some dumb little part and do that one little part over and over and over again until you get good at it. 

Which, let's face it, nobody very much likes. Well, sorry. Too bad. I mean really, its just too darn bad. Truth exists, and whether you like it or not the Truth is you never get good at anything any other way than by doing it. A lot. 

You want to know the truth? The truth is this fact is so well known I think every single one of us knows this very well. We just would rather delude ourselves and make excuses for our shortcomings, because this is a whole lot easier than admitting the shortcomings.

But hey, your life, your choice. You can make excuses. Or you can do the work.

Choose wisely.

A very human shortcoming is admitting our biases, we make excuses and delude ourselves but the fact they influence us is a very well known phenomenon. Cables, fuses, cable elevators, green markers, magic mats in the panel box ?? I would never hear a difference from any of these silly tweaks and knowing I have biases I also know I could never make an informed decision if I was aware these things were being tested or tried out. I could only make an honest decision if I was unaware but that’s just me I know I’m only human.