One for the Quiz?

[ashcatlt]

This will be fun. Reverse engineering this speaker switcher:
B-tech BT13

Describes thus:

☞ The speaker pairs are operated via a series-parallel switching.
The total impedance load on the amplifier can be calculated with the
table below. This is in relation to a speaker connection of 8 Ohm. With
a 4 Ohm speaker, the impedance values become half of the given value.

Speaker pair...............Total impedance (Ohm)
1 or 2 or 3 or 4 ...............8
1+2 or 3+4.....................16
1+3 or 1+4......................4
2+3 or 2+4......................4
1+2+3 or 1+2+4...............5,3
2+3+4 or 1+3+4...............5,3
all on..............................8
all off.............................100

I do believe it's all analog and all passive.

[newey]

On the link to the switcher, the "online shopping" link doesn't seem to have the product any longer. Too bad, I need one of these for the home stereo setup.

I have a plastic one that hasn't stood the test of time well.

Now, if I was to start taking quiz questions from the guy who's won it two years' running . . .

[sumgai]

ash,

Where'd you come by that table - when I visit the link, there's nothing like that that I can see (or navigate to).

But nice find, indeed a good brain-buster.


Let's see who nibbles at the bait. ;D




sumgai

[ashcatlt]

The question came up on the TapeOp board, and one of the posters found a PDF somewhere that included the text quoted.

[sumgai]

^^^^ I see. Shall we suppose that the PDF also has the "key", so you can check the answers?

Or is the really meant as an exercise in reverse engineering, so that newey can update his old box to something he understands, and can maintain with minimal effort?

;D




sumgai

[ashcatlt]

Actually, I don't have the answers, so maybe not a great true quiz question. Seems, though, that there's only so many ways it could be wired and actually accomplish all of the criteria.

It is an interesting thought experiment, I think. The (1 and 2) and (3 and 4) pairs are obviously series stacks, and are in parallel with one another. That part is relatively easy except that you can turn these on and off in any combination. As we know, on/off switching must be accomplished differently in a series structure from in parallel. So howdeydodat?

Then there's that "all off = 100" thing. I personally think there's probably just a 100Ω resistor parallel to the whole thing. It's enough bigger than the other values that it's impact on the total is negligible. So they've kind of fudged the table values a little.

[jcgss77]

On the link I get, it says it automatically sets the "most appropriate series or parallel configurations to suit the loudspeakers". Actually, it says it sets the configurations to "suite" the loudspeakers. Must be the suite spot...heh...sorry bout that...

Anyways, that is a challenge there, very interesting to say the least.

EDIT: Found one for ya Newey!

www.conrad.com/B-TECH-BT-13--SPEAKER-SWITCH.htm?websale7=conrad-int&pi=350733&ci=SHOP_AREA_37410_1310071

[newey]

Thanks, but it's from Europe, I hope to source one domestically. They're around from various sources, I hadn't really begun to look for one yet as it's down the list of priorities at the moment.