3 heads and one Cabinet - need switch

[tomb020871]

Hello,
I have a question for you all and I hope you can help me out. My situation is that I have 3 tube amp heads and one cabinet and would like to switch between the heads without having to switch cables all of the time. So, in essence, I would like to have the 3 heads go to the inputs on the junction box (that I will make) and then use a rotary switch and have one out to my cabinet. I also think I need to have a load resistor in place to protect me if I accidentally switch to another amp head without powering down my head? This would only be for safety. I do not intend to use this for switching between heads as I play. I would also like to have my guitar input on the switch box as well. Do any of you have a schematic that will accomplish this or is it possible to make one up?  This is just an idea for me and I really don't know how to do it. I know that a company called Radial Engineering makes something like this but it is only for 2 amps and I would really like to try to make something myself for 3 heads. I am thinking of using a rotary switch with 1/4 jacks. I can see the junction box physically in my head, I just can't see the electronic theory behind it at this time. Do you know how I would go about doing this and could you offer me any help in this situation? Anything would be greatly appreciated. I hope this is the right area to post this. I thought it may belong in the schematics catagory because that is ultimately what I am after. I wasn't sure.
Thank you for your help.

[jjasilli]

I think you need a hi-power SW(*):  ganged rotary, maybe 3 position toggle; and 2 dummy loads.  The selected amp head needs to be fed to the speaker cab.  The 2 un-selected heads each need to be fed to their own dummy load.  The dummy loads ea. should be 2X the distorted wattage output of the most powerful amp.  E.g., figure a 50W amp puts out 100W distorted.  The dummy loads should ea be 200W.  The dummy loads should probably be cooled by a fan.

(*)An ordinary rotary SW will not handle the power.

This may seem like overkill.  But if a guitar is left plugged into an un-selected amp; and that guitar and un-selected amp are inadvertently left dimed -- then that guitar may pick up sympathetic vibrations from the selected amp, pushing 100W silently into the dummy load.  

[tomb020871]

Thank you. I should have stated the heads that I do/will have. They are a Mesa boogie mini rectifier/25w, Marshall JCM1/1w, & a Vox Night train/15w. These are all being fed into a Mesa Boogie mini cab/60w.

Would I be better off making a foot switch with three separate buttons - 1 for each amp head?

[sluckey]

Use a SP3T for the guitar and a 3P3T heavy duty for the speaker. I don't recommend putting the guitar switch near the speaker switch. Here's the basic drawing...

[tomb020871]

Thanks Steve. When you say that you would't put the guitar switch close to the speaker switch, do you mean that you would use separate boxes or just put the jacks on opposite sides of the same box. I am not sure how to configure this. Sorry for all the questions but this is my first attempt at anything like this and I need all of the help I can get.
Thanks again.
Tom

[jjasilli]

I agree that 3 dummy loads are better, as it simplifies the switching, per Steve's schematic.  Since the most powerful amp is 25W, figure 3X 100W dummy loads.  100W = 2 X (25W distorted @ 50 W).  100W 8R power resistors are available cheap enough on eBay, e.g.  By making all 3 dummy loads 100W, you don't have to worry about plugging the big amp into the wrong dummy load. 

Don't know about the up-front guitar switching.  Maybe you want different guitars plugged into different heads???  Also, note with cables plugged in the input jacks on un-selected amps will be un-grounded

[tomb020871]

Is this possible to do this without the guitar switch? Just have the single guitar input going to the 3 different amps and using the one switch to switch between the amps or would this cause me to have 3 separate inputs (one for each amp) which would in turn, pretty much work the same as a switch?

[jjasilli]

The guitar SW is entirely optional.  You could simply plug the guitar into the chosen amp.  Alternatively, for the guitar is an ABC SW; here's a commercial example  http://www.musiciansfriend.com/amplifiers-effects/morley-abc-selector-combiner-switch/150561000000000

[tomb020871]

Could someone please recommend a rotary switch for this application? I am having a hard time finding one.
Thank you.
I am planning on using 4 swithcraft 1/4" jacks. One for the out to the cabinet and 3 for the ins from the amp heads. I am also planning on using the 100W 8R power resistors for the 3 separate load resistors. Is there anything I am missing other than the enclosure?
Thanks again everybody for all of your help. I really appreciate it.

[sluckey]

Could someone please recommend a rotary switch for this application? I am having a hard time finding one.

It's an odd switch for the guitar community. Just go to Mouser and start searching. You need contacts rated for 5 amps or more. It may not be cheap.

A 4P3T may be easier to find.

[tomb020871]

Why does the amp rating need to be so high?

[jjasilli]

Take your 25W amplifier into an 8Ω speaker load.  

1.  What is the voltage on the OT's secondary's circuit?  Power = Voltage²/Ohms; 25 = V²/8; V² = 25 x 8 = 200; V = 14.1421

2.  What are the amperes on the secondary's circuit?  W = V x Amps; 25 = 14.1421 X Amps; Amps = 1.8.  Round up to 2 and double that for safety (not to mention higher Wattage if overdriven) = 4 amps.  Probably a 5 amp rating is the closest available commercial product.

[tomb020871]

Take your 25W amplifier into an 8Ω speaker load.  

1.  What is the voltage on the OT's secondary's circuit?  Power = Voltage²/Ohms; 25 = V²/8; V² = 25 x 8 = 200; V = 14.1421

2.  What are the amperes on the secondary's circuit?  W = V x Amps; 25 = 14.1421 X Amps; Amps = 1.8.  Round up to 2 and double that for safety (not to mention higher Wattage if overdriven) = 4 amps.  Probably a 5 amp rating is the closest available commercial product.

Thank you so much. That makes total sense now that it is explained.

[tomb020871]

Thanks everybody for all of the great info and I am probably going to build my own switch but I have another question that may seem really stupid after all of the previous great info that you guys have given me but, If I plan on always powering down my heads before I go to the next one, what would be the problem with just going with a simple Y connector on the back of my cabinet for only two heads? Would this work? Don't shoot or loose faith in me for asking this question but I had to ask because I was asked and didn't know the answer.

[sluckey]

You asked for three heads! Two heads was always easy.

But, your Y connector will work fine in that situation until.... "some stupid with a flare gun..."

[tomb020871]

I know I asked for three heads and that is still the situation but for right now I only have two and need a quick fix until I can build one with confidence, unless you would be interested in building one for me? If so, let me know how much you would charge. I will eventually have 3 and wanted to prepare for the near future. Thanks again! You're the best Steve!

[sluckey]

This is only a hobby for me. I would never charge.

[stingray_65]

wouldn't a marshall style impedance selector work for the  speakers?

I might think a stomp box could be made with 3 dpdt switches and use dpdt relays that drop out when another switch is made.

so if all three heads are dialed in you could almost select them like pedals

like do some clean rhythms in on one amp the switch to another for  leads and yet another for some dirty crunchy stuff

[tomb020871]

I think I may have found the solution offered by a company called DeLisle. Check it out, what do you think? (scroll down to the de Lisle Amp/Cabinet Selector)
http://www.delisleguitar.com/index.php/pedals

[blomster]

Use a SP3T for the guitar and a 3P3T heavy duty for the speaker. I don't recommend putting the guitar switch near the speaker switch. Here's the basic drawing...

Hi,
Awfully sorry for necrobumping, but I can’t find anything like this anywhere.
If I wanted to do the same with just two amps instead of three, would a DPDT switch suffice, or would I need something else? The reason I’m asking is that I’m having trouble finding a 3P3T switch that can handle 4-5 ampere.
Cheers (and sorry for bumping)
Robert, Sweden

[acheld]

How about the rotary switches designed for impedance switching in an amp?

Like this:  https://www.tubesandmore.com/products/switch-rotary-impedance-selector-3-position

Or a switch designed for changing mains voltage input?

[pdf64]

Use a SP3T for the guitar and a 3P3T heavy duty for the speaker. I don't recommend putting the guitar switch near the speaker switch. Here's the basic drawing...

Hi,
Awfully sorry for necrobumping, but I can’t find anything like this anywhere.
If I wanted to do the same with just two amps instead of three, would a DPDT switch suffice, or would I need something else? The reason I’m asking is that I’m having trouble finding a 3P3T switch that can handle 4-5 ampere. ...

Yes, a DPDT could work for 2 amps. eg the common of one pole for the speaker cab, the other for the dummy load

[mresistor]

These are pretty good and inexpensive.  the shaft is tad smaller than 1/4" though.   https://www.tubesandmore.com/products/switch-rotary-1-pole-3-position-0