Multi input,one output

[einziger76]

I have been building a home studio and I have one room in which I have a mic'd cab and a separate room where my computer is located. At the moment my entire stacks are in the "amp"  room, however I am planning to move the heads to the control room and I want to make a pedal to do the following, have 3-4 inputs and one out put.  What I am wanting to achieve is the ability to have multiple heads run to the pedal or box I am thinking and then have one output going to a cab so I can run multiple heads to the same cab (only one head will be powered at a time). My question is would I need any resistors on any of the 1/4" jacks?  What I have envisioned would basically be an A/B/Y with out the switch.  Thanks for any help or advice!

[DIY Bass]

I can see a strong risk if you are talking about valve heads.  Disconnecting speakers from a valve head while it is powered is a very expensive bad idea.  I see quite a risk that a head could get accidentally disconnected while powered on. 

[einziger76]

I want to build a box like described to keep from having to unplug any heads going to a single cab.  I'll try to draw a picture and post of what I have in mind.

[einziger76]

[John Lyons]

I agree. Just use one amp connected at a time.
There is too much room for error. You may save
a little time and it may look neater but once
you blow an output transformer your going to
really wish you hadn't tempted fate.

[slashandburn]

Definitely not a good idea to do this as pictured. Way to much potential for bad and expensive accidents.

If it's an absolutely necessity, there might be a way to give the not-in use amps a dummy load, which might save your ass if you accidentally turn on the wrong head.  Either way, I know for sure that I wouldn't want my gear attached to anything like that.   That switch would need a cover, lock and key for sure.

[einziger76]

This is an actual drawing of what I had in mind.  I am lost as to what it would hurt.   Are y'all saying that if I made one of these and turned one amp on before turning the other amp off it could hurt one of the amps?  Is that the only way it could hurt one of them? Would they be ok as long as no two amps were ever powered up at the same time?

[PRR]

You should NEVER short the outputs of power amps together. They will fight each other.

This may even apply when 2 of 3 amps are off. If a 100 Watt amp is played loud, and a 18 Watt amp gets that signal on its output, the transformer tries to throw grossly excess voltage around the 18W. The tubes "may" survive. The transformer is at real risk.

A switch at least avoids putting big power into an idle/off amp. However tube amps without load are at risk if any large signal is fed to them. This leads to complicated multi-pole switching, which also needs isolation so the large output does not sneak-back to the small hi-Z hi-Gain input and howl.

[einziger76]

PBR, I'll try to word this so it makes sense.  Why couldn't I take a triple posistion switch and take all three grounds from the lines in and go directly to the output line, then take the three positives from the inputs and put on one position each of the switch.  Then say the switch had left, middle, right positions. Wouldn't this break the connection and eliminate the possibility of back feed?

[slashandburn]

Why couldn't I take a triple posistion switch and take all three grounds from the lines in and go directly to the output line, then take the three positives from the inputs and put on one position each of the switch.  Then say the switch had left, middle, right positions. Wouldn't this break the connection and eliminate the possibility of back feed?

You could. But you probably shouldn't, because:

.....tube amps without load are at risk if any large signal is fed to them.

If it's all your own gear and you're happy taking that risk, go ahead. If you're likely to hook amps belonging to other people up to this device I'd really beg you to rethink this.

[GibsonGM]

9.99 out of 10 people who work on amps and effects agree: you shouldn't do this unless you're willing to kill some of your (expensive) equipment.   

There are several REALLY EASY ways to make it work - if you want to try it out, go to it, but I don't think you're going to get anyone here to agree with the *idea*, because the consequences of ANY error, including human error, are expensive and a pain in the @ss, and unless you like the idea of buying and installing new output transformers etc...most all would stay away from doing this.   It's based on experience; maybe it will work fine for you (?), but I just don't see anyone endorsing it. 

[einziger76]

I'm not looking for an endorsement on my idea, I'm looking for a solution to surpass the flaws in my idea.  Isn't that what this forum is for?  If using a switch the way I mentioned previously wouldn't work then I was wanting to make sure it wouldn't before I make one and burn something up. But there has to be a way to do what I am envisioning and that is what I have set out to find.  If you cut one line of the output signal would or wouldn't it be able to receive back current is what I am trying to find out. 

[slashandburn]

You've solved the "power getting back to the unused/unpowered amplifiers" by adding the switch.    The potential for blowing your output transformer is still there as any device like you describe creates huge potential for running an amp with no load attached. Any switching arrangement conceivable (in my eyes) between tube amp and speaker will likely leave you exposed to this risk.

I'm not looking for an endorsement on my idea, I'm looking for a solution to surpass the flaws in my idea.  Isn't that what this forum is for?

Several people have all tried to help and advise you on this. All saying pretty much the same thing. I'd hazard a guess that nobody is telling you exactly how to build this speaker cab switching box because nobody wants to be held responsible when the inevitable happens.

[einziger76]

So the problem is turning an amp on with no cab attached? That's what causes the risk of burning up transformers?

[slashandburn]

Yes.

[einziger76]

Now we are getting somewhere.  Lol. I haven't ever heard of that and I've snatched cables out of heads and moved them around on different ohm outputs to see which one sounded better so many times it's not even funny. 

[einziger76]

So now my next step is to look into dummy loads as I have full intentions on continuing this idea.  Lol.

[einziger76]

Found a pedal to do exactly what I had in mind. 
http://n-audio.net/two-amps-to-cabinet

[slashandburn]

There seems to be another very similar unit called the Radial Headbone, apparently endorsed by the one and only Devin Townsend. It comes in three versions, for different types of amp. Might be worth a look.

I can see the appeal for touring musicians. Personally I'm still a bit dubious and wouldn't want to trust my gear with it.

I also can't help but wonder how many amps they burned through prototyping these devices.

[einziger76]

I saw a video yesterday of Mark Tremonti's rig and he was actually running a headbone.