For you EE freaks :P

Allen Ross · 04-23-2003, 07:12 PM

Okay I am only a Freshmen EE at UMaine and I have been getting the hardware itch recently, (must be all the assembly code I am learning) and I want to start my first real EE project. Seeing that this will be my first I don't want do anything too much, so I have decided to build a Speaker selector.

Okay I know it’s a really small project but I want something that is solid. When I say solid I mean something that will last my lifetime, and can handle any power that I through at it (500W). I don't see this as something that I will really need now but something that I will be able to use with any system I own in the future, or that my kids will have.

I am thinking of using really nice binding posts, none of this push terminal crap. With the ability to select 3 speakers minimum. I am also contemplating using knife switches (gold plated if I can find them to reduce chance of corrosion). I want to put this in a nice brushed aluminum box, or something similar. With the knife switches on the top or the side.

For a schematic, I will tie the ground to all the channels and I will just be switching the hot. Seems simple enough for me.

So my question is, where the heck can I find some of these components? The binding posts are simple PE or MCM, but the knife switches? I have no clue, same with the box.

Another thing is price, I am looking to spend no more the 100 bucks, I think this is very doable.

So tell me what you think, should I consider different switches?

Michael R Price · 04-23-2003, 09:10 PM

It sounds like a good idea, but I'm just curious... for what purpose do you need a speaker selector? I just sort of think that there are a lot of more interesting things you could build easily too... but, the selector which would definitely be something unique.

Allen Ross · 04-23-2003, 09:30 PM

so i can have multipil speakers going off of my reciver, when i go into speaker AB mode, it cuts out all my ablility to adjust levels, and it cuts out my ablity to use 5.1

I know i will be driving my reciver at a 4 ohm load but i think it can take it

(final last words)

Plus i can't really think of anything else to so as a small project

BTW, i haven't been able to find any knife swithces that can take any sort of real load, so i found these half way down theres some nice DTSP switches that can handle 20apms at 120VAC i think that should be heavy enough

Allen Ross · 04-23-2003, 10:42 PM

OOOohhhhh
Aaaahhhh

i think i found a project box

Hehehehe

i am enjoying this way too much

Dave Milne · 04-23-2003, 11:12 PM

Quote:

handle any power that I through at it (500W).

Since you're an EE, you know that a 20A switch will be good for 20^2*4 = 800W. However, I don't recommmend switching the thing at full power. Amp might not like this. Therefore, you can probably get away with lower-rated switches.

Quote:

ability to select 3 speakers minimum.

Three 8-ohm speakers equals 2.66 ohms. Not many receivers are happy with this

. Since you linked to a site about resistors... perhaps you're talking about including resistors to bring the minimum impedance up to 4 ohms. However, note that 1.1K resistors are not particularly useful in tnis application. If you're seriously comtemplating a "smart" switch box that simply parallels any two speakers for 4 ohms and inserts resistors to, say, two of the three if three are selected... you're talking about a significantly more complex project. And it will require some SERIOUS resistors for 500W capability.

In this case I recommend putting enough smarts into it to know to series-connect two of the three if all three are selected. This will, of course, require some simple digital logic driving relays.

Also, make sure you isolate the speaker/amp common ground from chassis ground. True differential amps float the return.

See now, there in the true spirit of engineering, I have turned a simple switch box into an elaborate combination of digital logic (maybe a simple microprocessor

), power supply, relays, etc.

**HTF Ads**

Paul Stiles · 04-23-2003, 11:12 PM

Another possibility is using switches to control some DC controlled (coils rated for DC voltage) relays that have heavy duty contacts. If you are really persistent/lucky, you may get some relays in hermeticly sealed cases that have nitrogen (or some other relatively non-reactive gas) inside.

Paul

Allen Ross · 04-23-2003, 11:42 PM

yeah i don't know why that link worked
heres the correct one.

I thought about the switching under load and i came to the concustion that the best way to do it is just shut off the speakers when i am switching.

I still have to work out the Resistance of the selector, i think if i just put some resistors in parrale, or have a toggle switch that can add a resistor in series to the curcuit then i think i will be all good.

BTW i like the over kill on the switches, you never know what i will be running

Nothing is excessive like excess

Brian Knauss · 04-24-2003, 02:06 PM

The 6A switches are basically overkill. You receiver is never going to put 100W out per channel (unless you clip it like crazy)

Don't get the WBT overpriced binding posts. Just get the good ol PE gold plated ones. Call it a day and then look at your fatter wallet.

Still lost on this whole reason for the project. Are you trying to duplicate the sound from each channel to the rear speakers? You'll have a harder time correcting the imaging among various other problems. Doesn't your receier have a handful of settings that use the surround outputs?

Allen Ross · 04-24-2003, 04:33 PM

i am doing this to mirror image the settings that my reciver can do with surround sound and my A speakers. its really werid

when both A and B are on, i can only adjust A's left and right, and no sub. I will mainly use this when i want to have the same sound in multiple rooms, IE have one set in one room and another in another, and still have the ablility to adjust, my levels. I might put the slector on my surrounds and have them switch between room speakers or i might have my mains, i still haven't made my mind.

As for the switches, i am all about putting high current through this beast I will have to agree that 30A is a little much, but i want this thing to stand out and have some authority. Plus i don't know what kinda power i will be using this with. I might even use it for a sub switch, cutting power from one driver to another if i have multiple subs, one for muisc/one for HT, you never know. But i juat want this thing to not be the limiting factor in my system.

I have also contemplated another isusse, isolation, if i am going to snag that nice aluminum case how am i going to issolate the singnal from the chasse, some rubber washers or will it just be fine with the supplied hardware?