Building a simple A/B box for comparing amplifiers - relays, or just a mechanical switch?

[UsableT]

I've got an old Kenwood that still works well. I also just bought a new AudioEngine N22 (solid state A/B) and am curious whether my aging ears will be able to hear much of a difference if I use the same input (a DAC connected to my computer, for the music) and same speakers. Thus I will build an A/B box not for swapping speakers, but swapping amplifiers. I'll also need a box to swap the DAC in between the amplifiers; and of course a way of measuring output level for each amp to make sure I set them both about equal.

I haven't thought much yet about the A/B box for swapping the DAC from one amplifier to another, because I'm still working out the details for swapping the speakers from one amplifier to another.

I did some doodling on my own & then went online to look at what other folks have done. Two possible routes seem to be 1) just use a mechanical DPTD switch, or 2) use relays that perform the DPTD duty, and add a mechanical switch on a long lead that goes to the relay; thus allowing you to sit back in your chair to do the switching.

The purely mechanical route would be something like this person did: http://audio-room.net/connecting-2-...eakers-making-an-ampspeakers-selector-switch/

The option to add relays would be more like this article on Rod Elliott's site: https://sound-au.com/absw.htm

And here is someone else's recipe for a relay-equipped switch: https://www.audiosciencereview.com/forum/index.php?threads/ab-x-testing-of-power-amplifiers.20464/ Note that the schematic is only for one channel, so you would need to double it to serve the other channel, I believe. With a relay with enough contacts/throws this could be done - he uses a type of relay that I frustratingly cannot sufficiently identify to make possible a search for something similar on DigiKey or Mouser).

I like the idea of the relay version & being able to back in my chair and push a button from there without having to get up & go over to the amplifiers to fuss with the switch. (I'd have to come up with a long-lead pushbutton for the DAC switch, too, obviously.)

My big hangup here: I've never worked with relays before; so first step is I'd need to learn how to buy one with suitable values. It's not much help for me to go to DigiKey or Mouser until I know the parameters that will suit.

So I guess my question is, has anyone worked with relays enough to recommend particular values (e.g. switching voltage, max amps & volts, etc.) for appropriate SPDT or DPDT relays? That would make life simple enough for me that I could go shopping & work up something I could build pretty quickly.

Thanks in advance -

 

[audiodummy]

If I was listening for myself I wouldn't bother, if it sounds right as is... ignorance is bliss.

If I needed it to demonstrate for someone else, then would be nice to rapidly switch between different amps and speakers even... A crossbar is ideal so you can switch anything to anything, but that gets complicated fast.

I'll assume most people here are using bipolar or bridged amplifier outputs, and not (capacitor coupled) single ended, so you will need to switch both + and - to the speakers. So rule out the SPDT option - you'll need DPDT switches or relays. Note that with relays you will not have a neutral position, one amplifier will always be connected. A mechanical switch can have an off position - if needed for a relay solution, you need another relay.

Generally speakers are "low" voltage and "medium" amps. Without knowing how many watts you're planning to pump to your speakers it's hard to know what you need.

That last website is using quick-replace octal relays. Seems you can still get them - https://www.grainger.com/category/electrical/industrial-controls-automation-and-machine-safety/relays-and-accessories/plug-in-relays?attrs=Base+Type+-+Plug+In+Relay|Octal&filters=attrs#WP8118009 - though it's not mandatory you get them. Just need to ensure you have the right number of poles, maximum voltage and current rating of the contacts, and the coil ratings on what you're planning to control it with. And yeah it looks like they still make 4PDT relays so you can control two bipolar output stereo amplifiers to two speakers with one relay...

 

[UsableT]

Thanks audiodummy - I really appreciate your response.

To start with, I agree with your sentiment about audio gear that in general, "if it sounds right it is" - in fact for me, with my aging ears (I'm 66), I'd go so far as to say "if it even sounds 'just okay' then it is." Most of my gear is used stuff, picked up by me via Craig's List or the recycling station & as necessary fixed up by me (e.g. I did a big job, for me, of removing static from my lovely Kenwood KR-4070 by taking apart each and every noisy rotary switch so I could clean them properly; plus I was even able to restring the mechanical tuner, thanks to guides posted on this very forum!).

The single exception is that I play piano, and have a great setup for PianoTeq software + a high quality keyboard + a nice DAC going into a nice set of headphones (Beyerdynamic DT 880); and I am exquisitely sensitive to sound when using this setup.

For whatever reason I have now gotten the yen to be able to play this same digital piano setup, but through speakers - and man that is a tall order. For whatever the reasons, a given set of amplifier + speakers can do just fine with recorded music - but sound like absolute crap in reproducing the digital piano sound generated by the PianoTeq software.

One thing I've discovered that makes a big difference is proper room EQing, for which I use REW. It's amazing what EQing can do. I also tried building some DIY flat panel speakers, but my designs were crude and anyway I am not sure that the Dayton exciters I bought via Parts Express will ever be able to do the job - at proper volume to match an acoustic piano, the exciters simply cannot handle the mid-range or bass fundamentals expressed by the piano software - not even with the help of a really good software. The standing resonances are just too much for exciters. So next I am going to try EQ'ing some of my regular speaker sets (most of which I rescued from the recycling station & fixed up as needed w/ new crossovers & tweeters, etc.) to see if they can do better.

Anyway this is all to say that I wanted to see how the N22 would do against the Kenwood for this purpose. I already know, from a brief tryout, that what it definitely wouldn't be adequate if I were sticking with the flat speakers - not enough power at 20W RMS at 8 ohms. The flat panels I built were pretty inefficient so the N22 may do a bit better with regular speakers. We'll see . . . or not.

Why even think of the N22 or something like it? For reasons of physical space. My piano setup has to live in my little home office, and the Kenwood sucks up an awful lot of room jammed in between my keyboard and my desk and desktop computer. A little bitty guy like the N22 would make life much easier - I don't like working or for that matter playing music in an overcrowded room if I can avoid it.

As for the rest of your answer - very very helpful. I also have a couple of books on electronic components that are well-written, and one of them has a good chapter on relays. So with your advice plus that book, I think I will be ready to do some shopping. That's if I go through with the whole hare-brained scheme . . . or if I just wanna do it to have fun building something, a fit which periodically overtakes me for no practical reason.

So thanks again.