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.

[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.

[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.

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.

[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.

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.p...or-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.

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.

`

[BMWCCA]

Todd,

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

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