A/B/X Speaker Selector With Level Matching for <$100

[toddalin]

Let's see if this will post before I get into it again.

[toddalin]

Interesting. Whenever I try to cut and paste text from AudioKarma to here, it times out and locks up the site. Weird!This is the message displayed:

This site can’t be reached


www.audioheritage.org took too long to respond.
Search Google for audio heritage org vbulletin edit post
ERR_CONNECTION_TIMED_OUT

[BMWCCA]

I searched BarterTown for something similar but came up empty. :dont-know:

[toddalin]

OK, I guess I'll have to do the text from scratch:

While comparing the L112s and the modified L200/300s I thought it would be nice to be able to instantly compare speakers with level matching so that any differences in volume are taken out of the equation. And wouldn't it be really cool if we could remotely select either speaker either by choice or at random for comparison to the other? With the advent of cheap electronics out of China and from ebay and no/little international shipping costs, this becomes easy to do. Major expenses are included. With the exception of a case, and a terminal plate for the 12 speaker connections (4 in/8 out and ~$10 on ebay) I have everything else (switches, wall wart, perf board, 555 chips, wire, etc.) but it doesn't amount to more than ~$20.

[BMWCCA]

A link might be nice, so we can have some context. :dont-know:

[toddalin]

Actually, I've tried posting into here by cutting and pasting from another site, from notepad and from Word and all do the same damn thing..., lock me out of the system. :banghead:

It's as if if I don't type it here, it's not going to go here. Anyway, here is a condensed version.

:::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::::::::::::::::::::::::::::::: ::::

This is for an A/B/X speaker switcher with the capability to match levels..., or not. With a set of jumper wires between the A and B outputs, it can also be used a partial and full mute for the system.

I've not ever seen any similar units offered for the consumer though I have heard of them being used in the professional world for speaker evaluation.

This uses a 4-channel, 12 volt key fob transmitter/receiver with buttons marked A,B,C, and D ($9 from China including two key fobs)

Pressing A or B (set to momentaneous) instantly brings on speaker A or B.

Pressing C (i.e., "speaker X") (set to momentaneous) makes the unit go mute until released. When released either speaker A or B will come on at random. An LED on the panel indicates which set is playing.

Pressing D (set to interlocking) mutes the system and pressing it again brings it back on.

When "mute", the amp is routed to two 100 watt 8-ohm resistors to avoid damage to the output stages.

The audio signal L-pads are stereo 100 watt. The 4PDT switches by-pass the L-pads while still allowing all switching capabilities. I'm using USA-made Eaton 15 amp 250 volt switches with silver contacts. The audio relays are rated for 40 amps with silver contacts. When done, (I've started to receive parts), this could be available for So Cal members use in demos.

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_120_Nov_25_16_26.jpg

[BMWCCA]

Actually, I've tried posting into here by cutting and pasting from another site, from notepad and from Word and all do the same damn thing..., lock me out of the system. :banghead:

It's as if if I don't type it here, it's not going to go here. But . . . have you tried simply posting a link to the thread?

OfcourserightnowVbulletin'sspacebarisn'tworkingifI spacedownonecarriagereturnfromtheoriginalquotedpas sage.;)

[toddalin]

Sort of a moot point now. At least my space bar works..., for the moment. ;)

[rusty jefferson]

http://audiokarma.org/forums/index.php?threads/a-b-x-box-with-level-matching-for-speaker-comparison-for-100.743594/

Some members of our local diy audio club have built one that we use pretty regularly. It's an awesome tool. I'll see if there's a schematic available.

[Ruediger]

The relay contacts will corrode over time and thus add resistance to your amplifiers output impedance. And the L-pads will add resistance from the beginning.

Your amplifiers output impedance affects the Qt value of the speaker, it wil make it greater. This will detune vented bass boxes, it will make them "boom".

You wanted to compare speakers and not boom boxes, right?

You could build a switching device from a home theatre amp with plenty of channels and switching before the amps instead of after.

Ruediger

[toddalin]

Corrosion is why I used high amperage silver contacts. Lots of surface area and a strong push to keep things together.

My amplifier has an A/B speaker selector, as do most. No one seems to worry about corrosion in those contacts, which probably have nowhere near the amperage rating of what I'm using. :dont-know:

As for changes in sound, that's why the L-pads can be switched in/out. Ultimately the RTA and listening will tell if there is a notable difference in the FR/sound between the two scenarios.

[toddalin]

OK...,

After a few design changes based on bread boarding on the test bench, I got the "randomizer" working nicely and worked out the component values. I'll put the revised schematic up after its done.

[toddalin]

I knew that this was somewhere in the back of my brain from way back when:

https://en.wikipedia.org/wiki/ABX_test

[toddalin]

OK, as promised, I've included a revised schematic showing all of the component values (except the 12 volt power supply and it's LED).

Note that this can also be used for switching components, sans L-pads. In that case, use shielded wire and you don't need to use the heavy duty relays and switches as I used for the speakers. In fact, the speaker relay could be just another "gang" on the "latching" relay and the mute switch would simply open the circuit rather than route it to the 100 watt resistors.

`http://www.audioheritage.org/photopost/data//500/ScreenHunter_123_Dec_14_15_17.jpg

[BMWCCA]

Todd,

Thanks for that. I hope I have the time to build one some day. A parts list would help me, too! :D

Is it possible to see a shot of your finished product?

[toddalin]

The part list is included on the schematic. Change R6 to 220K ohm so you don't have to wait quite as long for it to reset each time.

Right now it's operating on a "breadboard." I need to solder the pieces on a perf board and pull the power supply from an old Altec computer speaker system.

Also, I made the sides and front for a cabinet (with the holes for the 12 speaker jacks spaced for dual banana plugs in one side) but the face came out a bit too small. These were done in clear acrylic and cut on the laser cutter. The back and bottom of the chassis are from an old CD player. The two RCA plugs on the back of the chassis (from the CD player) will serve as plugs for two lights that can go on the speakers to indicate which is playing, if so desired.

For some reason Corel re-scaled the face a bit and I need to redo it. Anyway, the second itteration will have the hole for the Mute LED and the Mute and speaker selector switch, which I didn't include the first time. It will be more convenient having these features on the face for set-up or just when standing next to the system, as well as on the remote, though I don't really see the need for the randomizer on the face plate.

I'll get pics when done.

[BMWCCA]

The part list is included on the schematic. Change R6 to 220K ohm so you don't have to wait quite as long for it to reset each time.Thanks, I see it now! Had to zoom in on the laptop (and take my glasses off!). I appreciate your work. It's something I could certainly use. An early Christmas present from you to us!
:tree:

[Odd]

Thanks, I see it now! Had to zoom in on the laptop (and take my glasses off!). I appreciate your work. It's something I could certainly use. An early Christmas present from you to us!
:tree:


The man in the tree, waving the Norwegian flag?

74972

[toddalin]

Thanks, I see it now! Had to zoom in on the laptop (and take my glasses off!). I appreciate your work. It's something I could certainly use. An early Christmas present from you to us!
:tree:


ItwascommentedthattheuseoftheLpadscouldcompromiset hedampningoftheamp.Assuch,Iwillmodifythecircuittoi ncludepassiveattenuatorstogobetweenthesourceandrec eiverorpreampandamp.Thedevicewillallowforeithermet hodofattenuation.Thelogicisinplaceandit'sjustamatt erofaddingacouplemorerelays/wires/plugs/pots.

Oh, I the space bar is doing it's weirdness again. Interesting that the first line ran together, but not this one. WEIRD!!!

[toddalin]

Thanks, I see it now! Had to zoom in on the laptop (and take my glasses off!). I appreciate your work. It's something I could certainly use. An early Christmas present from you to us!
:tree:


Unfortunately, my schematic program doesn't output to a format that can be read by the forum, so I end up using ScreenGrabber to capture the image and put it on my desktop. That puts it into jpg, but I loose resolution.

Let me know if ther is anything you can't read.

BTW, I am modifying the circuit so that it can use the L-pads and/or passive attenuators in the line level audio path. I believe I even have the necessary parts and relays to do this. Back to the bread board!

[toddalin]

I've included a revised schematic that allows you to either/both attenuate between the source/preamp and power amp and/or between the power amp output and the speakers. The passive attenuator for the source/preamp uses stereo 100K pots in a voltage divider arrangement and triggers to the appropriate set with the speakers. This gets around any speaker damping issues. This can be defeated using the switch.

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_124_Dec_15_16_27.jpg

[toddalin]

Todd,

Thanks for that. I hope I have the time to build one some day. A parts list would help me, too! :D

Is it possible to see a shot of your finished product?


Awaiting parts from China. Meanwhile, the working breadboard:

http://www.audioheritage.org/photopost/data//500/Resized_Breadboard.jpg

[toddalin]

The board is now all soldered up and the A/B/X and wireless remote functions are really cool. I made some changes to the original schematic and included the revised version.

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_125_Dec_28_16_50.jpg

[BMWCCA]

Thanks for the update!

[toddalin]

I've now mounted all of the components onto an old CD chassis. I made a new faceplate and sides from acrylic and still need to cut the top with the laser.


This works really cool except that the relay that switches the line level signal was an old surplus piece and it has high resistance (corrosion) on the N/O contacts leading to reduced volume in that position. Of course the two channels can still be made to be the same level, but there is a loss of several dB when the attenuators are switched in. I'll order a quality piece to replace this relay and life is good. When done, I'll get some pics and maybe a video.


This will be available for forum member to use in any forum demos in Orange County CA area. I designed it so that someone can monitor the panel and there is a switch such that a 12 volt light can be placed on the speakers that will come on when that speaker plays. But the panel switch can also turn off the speaker lights and or the panel lights so blind and double blind testing may be performed.

[toddalin]

I finished out the case today and snapped some pics.


The chassis/back are from an old cd player. The original RCA jacks on the back now send 12 volts to a pair of lamps that can be placed on/near the speaker to indicate which is playing. This is also displayed on the panel and both are defeatable. The new RCA jacks are for the source attenuators.


http://www.audioheritage.org/photopost/data//500/medium/DSC_00442.JPG
http://www.audioheritage.org/photopost/data//500/medium/DSC_00462.JPG
http://www.audioheritage.org/photopost/data//500/medium/DSC_0047.JPG

[toddalin]

All done.


I had to replace the audio relays because the pieces I originally used were less than steller quality adding as much as a few hundred ohms and reducing the volume. The replacements were used in a professional audio mixing board and are sealed with gold contacts.


Switches and pots from left to right: Power (Off/On), Panel Lights (Off/Panel/Panel and Rear RCA Jacks), "A" Channel Line Attenuator, "A" Channel L-pad Selector (Off/On), "A" Channel L-pad, "B" Channel L-pad, "B" Channel L-pad Selector, "B" Channel Line Attenuator, A/B Channel Selector, Line Attenuators (Off/On)


LEDs in center of panel: "A" Channel (Green), Mute (Upper Yellow), Power (Lower Red), "B" Channel (Green)


Switches on Remote: "A" ("A" Channel) "B" ("B" Channel) "C" ("A" or "B" Channel at Random) , "D" (Mute)

If anyone in So Cal wants to do a speaker demo and use this, I'm good with that.

http://www.audioheritage.org/photopost/data//500/medium/DSC_0054.JPG

http://www.audioheritage.org/photopost/data//500/medium/DSC_0056.JPG

The original CD outputs now provide 12 volts in accordance with which channel (A/B) is playing and switchable on the front panel. The gold jacks are for the line attenuators that go anywhere in the audio chain between the source and amp. When "Random" or "Mute" is selected the amplifier's outputs goes to 10 ohm, 100 watt resistors until released.

http://www.audioheritage.org/photopost/data//500/medium/DSC_0057.JPG

[toddalin]

This thing works great and the only way to compare speakers!

I was running my L112s against the modified L200/300s. I noted that the L112s had a much more centered "center" whereas the L200/300 seemed more "ambiguous" in this regard.

Soooo, I found it has another use for the box..., phasing of the components.

I disconnected the horn leads and using the "+" terminals of the box, I was able to use the box to instantly flip the polarity of the horn driver and listen/compare it both ways. As is was, I had the polarity with the driver's + on the crossover's - because this is what the 61-band RTA seemed to show as having the flatter response in the room when I set them up. Recognize that the JBL 2235 woofer has "reversed polarity" and I run amp's - wire with the the speaker's + lead, accordingly to maintain phase with the system, so connecting the horn driver in this manner actually puts it out of phase with the woofer, but in phase with the system.

With the abillity to instantly switch, I found that I had this wrong and changing the polarity to the horn driver (2420 with tangential diaphragms on the longer L300 horns) increased focus, intelligability, and crispness enough that I could easily tell the difference, even in A/B/X testing.

Then I did the same for the 2405 tweeter and also found that I preferred the sound, again with the polarity reversed from what it was (previously crossover's - on tweeter's + to maintain system phase), but this was very hard to A/B/X and tell the difference consistently.