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Discussion Starter · #1 ·
I am looking for ideas and suggestions to achieve more or less the following:

What?
- setup = a failsafe/foolproof and extremely convenient way to play multiple amps though a single speaker cab
- several amp heads, 1 speaker cabinet
- allow one touch switching of both amp head AC power and speaker connection
- several or even 10s of seconds delay between switching is acceptable ie not for live in-play use

Why?
- don’t ever want to allow amp to power up without a speaker load, in particular accidentally
- access to the back of the amp heads is inconvenient after initial setup
- need to manually move cables is inconvenient and prone to error, potentially allowing a head to power up without load

How? (ideas)
- midi controlled multiple switch AC power switcher + midi controlled 1/4” TS speaker line relay switcher
- midi controller able to store command sequences for above activated by a single midi user input (button, switch)
- midi controller must allow sequencing a break-before-make sequence ie so that no two amps can ever be on simultaneously even for a fraction of a second (example switch sequence is: power all off, pause, switch speaker route, pause, power specific amp on)

Bonus!
- ability to deal with variety of amp head impedance loads by switching in an extra cabinet when appropriate; a completely independent 2nd set of speaker routes is likely sufficient ie speaker switcher above are two paths switched by a single (or equivalent to single) command

Any ideas? A single product incorporating above would be simplest, but I am not clear such a thing exists.
 

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I have a Metropoulis head switcher for sale in the classifieds. It does NOT do EVERYTHING you desire, I'm not sure it's possible. It doesn't mess with power (amps are always on), it doesn't have any delay when switching (stomp switch), it does not allow for changes in impedance. You run 2 heads through 1 cab (or set of cabs).

Radial also makes the Headbone. I'd bet there are more complex *things* out there that can do some more of what you want, but I've looked and not found them so far.
 

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I've never seen anything like that commercially available. I'm sure one of those high end 'custom pedal boards for the pros' kinda builder could put one together, but I'd be afraid of the price. I'm sure you could string together a couple Metrolopouli or Headbones for much, much less.

If you are killing AC to the amps, you don't really need to worry about extra loads - you just have to ensure the amp getting powered up is terminated with the speaker. Some clunky old 1T2P relays (route power and output signal with one switch operation) could be config'd to do it, but again you're probably paying someone to put it together. And it could be kind of clunky in operation, since yours would be beta.
 

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Why not send pete thorn a msg on twitter or on the other forum...from his studio setup, i bet he could point you in the right direction
 

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Discussion Starter · #5 ·
Thanks guys, some good suggestions. No viable solution yet, however. I have a feeling I am going to have to build it myself. If I do it myself, I’ll do multiple cabs and I’ll do guitar input switching for good measure. Man, that is going to be A LOT of relays.

In any case, here are my comments so far:

- I didn’t mention it, but I am looking for many more than 2 heads; 6-8 would be ideal; so the 2 amps/1 cab switches won’t cut it

- this is one unit and is a nice approach that doesn’t require AC mains switching, but $1500 USD ... Product :: CAE Amp Selector
 

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A real simple solution could be a jackfield.

I used to use 1/4" jackfields that would normal through the signal (top jack to bottom jack) until you inserted a plug into the top jack. You could wire your amps across a row of eight or ten jacks and have the bottoms normal'd to separate 8 ohm load resistors. And have one bottom jack that terminates in the actual 8 ohm speaker cabinet. Jumpering any amp output to the speaker input will lift the dummy load. All amps stay terminated in either the dummy load or the actual speaker. Probably cost a couple hundred or less in parts. Totally manual operation though.
 

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Discussion Starter · #8 ·
That’s an interesting idea by @High/Deaf, thank you! Need to think about the somewhat decreased convenience.

@greco, that approach would not need AC mains switching as the primary purpose of AC mains switching in my described setup was to ensure an amp is off if no load. In @High/Deaf setup, each amp remains loaded, so mains off is not as critical.
 

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the primary purpose of AC mains switching in my described setup was to ensure an amp is off if no load.
Gotcha!

Many years ago, I started a thread asking this question...

"How long would it take before an unloaded tube amp would incur OT transformer damage IF the amp was only idling."

I did that to one of my amp heads and was scared sh!tle$$

Many amp techs responded.

Unfortunately, the thread was lost.

Care to hazard a guess as to the responses?
 

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Discussion Starter · #10 ·
It’s a good question in general and related to this thread. I’ve wondered that myself. I have no imperical or experimental evidence, but I would think there would be two issues at play: thermal heating and stability. From the thermal point of view, I think it could idle with no load (ie infinite impedance) indefinitely. However, I would be concerned with a runaway oscillation (ie instability) even when idling, so I don’t think you’d want to risk that for longer than a few seconds as my “formal guess”. What do I win?
 

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It’s a good question in general and related to this thread. I’ve wondered that myself. I have no imperical or experimental evidence, but I would think there would be two issues at play: thermal heating and stability. From the thermal point of view, I think it could idle with no load (ie infinite impedance) indefinitely. However, I would be concerned with a runaway oscillation (ie instability) even when idling, so I don’t think you’d want to risk that for longer than a few seconds as my “formal guess”. What do I win?
You are correct about the idling with no load for long periods. We didn't discuss "runaway oscillation"/"instability".
Some of the amp techs reported forgetting and leaving them idling with no load for several hours.

As mentioned above, I forgot mine for a few minutes and was very worried. I was a 60's Bandmaster head. I built a dummy load for it (VISHAY power resistor ...8 Ohms @ 75 watts ...IIRC) and played into the dummy load for maybe 30 seconds with the volume about 50% or so. The heat sink of the dummy load got plenty hot, plenty quick!

You win a coffee and dessert at the City Cafe near Sherwood Music (or similar). This comes with a free set of steak knives ...one of the many that I have accumulated through the years. PM me to schedule.
 

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Same as a patch bay? "Jackfield" is a new term for me.

Would this also handle the AC power to the heads?

Yes, similar to that, except the 1/4" jacks are paired like this:



The ones I've used were only 'single normal' - just the top jack had the switching. So any signal from the 'source' (the amp's output) would pass through to the 'destination' (wired to a dummy load or speaker) until a plug was inserted in the top jack, at which time the 'source' signal would then be routed through the cable, probably to the 'destination' jack feeding the speaker. Of course, you could have multiple speakers connected to different 'destination' jacks, making A/B'ing different cabinets a very quick endeavor.

But the system isn't foolproof. They are inherent dangers if you aren't careful (like plugging a cable in the 'source' and forgetting to terminate it in a load of some sort).
 

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contact bob from custom audio electronics. he has a head switcher with line out as well so all your amps can share the same effects.
i eventually will order one.
 
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Tim Pierce uses one or 2 rack units for his amps. He goes through them on a video where he explains his studio setup. It's a newer video, there are older vids 2014 but the amp selector has changed. Maybe it's one of the Tim and Pete shows...
 
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