Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  
previous: Mark Lavelle Is there any way to wire a DPDT on-... -- 5/30/2004 6:41 AM View Thread

Re: 2x12 speaker select switch?

5/30/2004 12:45 PM
Re: 2x12 speaker select switch?
Is this an open or closed back cab?  
The reason I ask is because I found a solution for the same options on a Mesa Boogie 2-12 vertical, slant, half back cab that I picked up for $80 at a pawn shop. (2 EVM12L's...some yutz painted the grill and the logo. It said Messy Booger, but it cleaned right up).  
This would have been harder to do on a fully closed back cab, without hacking the cab.  
I took a small Radio Shack aluminum project box, and used the bottom. I broke off one side, and smoothed down the edges and corners. The "U" shaped box was now "L" shaped.  
I disconnected the top (open half) speaker wire that was connected in parallel to the bottom speaker, and fished that back through the hole.  
I fitted the bracket with two 1/4" jacks, and wired them in parallel, then wired them to the top speaker. I mounted the plate a few inches in behind the top speaker.  
Now, I can use them seperately, as two 8 ohm loads, or as one 4 ohm load.  
Use two amps? Just plug an amp each into the top and bottom jacks seperately. Two 8 ohm loads. Two speaker cables.  
Use both speakers for one amp? Plug amp into one of the jacks in the top speaker plate, then plug another cable from the other (paralleled) jack into the existing, non-modified bottom speaker jack. One 4 ohm load. Same two 3' speaker cables.  
Easily reversible, handy little mod. All it will leave is two small screw holes, but I can't imagine anyone wanting it original when they have options, unless thay ALWAYS use it that way.  
A closed back cab would present more problems for doing this. Obviously, you'd need three jacks. If you were going to cut a larger hole anyway, may be an option, though. You'd just have to be VERY careful about plugging in two amps. You wouldn't want to plug them both into the paralleled jacks. (It's more obvious on my cab). Maybe group the paralled ones closer to each other, and mark them. Then, all you would need is a short jumper speaker cable.  
This seems like it would give you even more options than either A or B alone, and both. This would give you A AND/OR B seperate, and both paralleled, which is about the same as my Marshall 1960 Vintage cab.  
Of course, you could probably just buy a switchplate similar to the Marshall. Or, buy one of those recessed blank panels, and build your own, making sure the toggle switch doesn't stick out the back of the recessed panel so it doesn't break if you put the cab on it's back, or something.  
I thought about some kind of a switch, but decided to use the easier method, which seems to work fine.  
I looked at it like each amp was now going to it's own speaker cab, and there was no common ground shared at the amps' outputs. (The Marshall seems to share a common ground, even when switched to stereo. What effect does this have in several scenarios? One player, two amps. Since the amps are supposedly grounded to each other through the signal path at the inputs, what happens when they ground to each other at their outputs, also? In the unlikely event that two people are using each half through seperate amps, they aren't grounded together at the inputs, but maybe (or maybe not properly) through the power plugs into the building's electrical circuit. Then the output grounds meet at the Marshall. Any concerns here? Or, is ground is ground is ground? More is better, or ground loop problems? Sorry, this just occurred to me as I was gulping coffee and writing this.)